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24
docs/notes/Leetcode 题解 - 二分查找.md
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@ -96,7 +96,9 @@ l m h
# 1. 求开方
[69. Sqrt(x) (Easy)](https://leetcode.com/problems/sqrtx/description/)
69\. Sqrt(x) (Easy)
[Leetcode](https://leetcode.com/problems/sqrtx/description/) / [力扣](https://leetcode-cn.com/problems/sqrtx/description/)
```html
Input: 4
@ -134,7 +136,9 @@ public int mySqrt(int x) {
# 2. 大于给定元素的最小元素
[744. Find Smallest Letter Greater Than Target (Easy)](https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/)
744\. Find Smallest Letter Greater Than Target (Easy)
[Leetcode](https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/) / [力扣](https://leetcode-cn.com/problems/find-smallest-letter-greater-than-target/description/)
```html
Input:
@ -168,7 +172,9 @@ public char nextGreatestLetter(char[] letters, char target) {
# 3. 有序数组的 Single Element
[540. Single Element in a Sorted Array (Medium)](https://leetcode.com/problems/single-element-in-a-sorted-array/description/)
540\. Single Element in a Sorted Array (Medium)
[Leetcode](https://leetcode.com/problems/single-element-in-a-sorted-array/description/) / [力扣](https://leetcode-cn.com/problems/single-element-in-a-sorted-array/description/)
```html
Input: [1, 1, 2, 3, 3, 4, 4, 8, 8]
@ -205,7 +211,9 @@ public int singleNonDuplicate(int[] nums) {
# 4. 第一个错误的版本
[278. First Bad Version (Easy)](https://leetcode.com/problems/first-bad-version/description/)
278\. First Bad Version (Easy)
[Leetcode](https://leetcode.com/problems/first-bad-version/description/) / [力扣](https://leetcode-cn.com/problems/first-bad-version/description/)
题目描述：给定一个元素 n 代表有 [1, 2, ..., n] 版本，在第 x 位置开始出现错误版本，导致后面的版本都错误。可以调用 isBadVersion(int x) 知道某个版本是否错误，要求找到第一个错误的版本。
@ -230,7 +238,9 @@ public int firstBadVersion(int n) {
# 5. 旋转数组的最小数字
[153. Find Minimum in Rotated Sorted Array (Medium)](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/)
153\. Find Minimum in Rotated Sorted Array (Medium)
[Leetcode](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/) / [力扣](https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array/description/)
```html
Input: [3,4,5,1,2],
@ -254,7 +264,9 @@ public int findMin(int[] nums) {
# 6. 查找区间
[34. Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/)
34\. Find First and Last Position of Element in Sorted Array
[Leetcode](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) / [力扣](https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/)
```html
Input: nums = [5,7,7,8,8,10], target = 8

48
docs/notes/Leetcode 题解 - 位运算.md
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@ -61,7 +61,9 @@ static String toBinaryString(int i); // 转换为二进制表示的字符串
# 1. 统计两个数的二进制表示有多少位不同
[461. Hamming Distance (Easy)](https://leetcode.com/problems/hamming-distance/)
461. Hamming Distance (Easy)
[Leetcode](https://leetcode.com/problems/hamming-distance/) / [力扣](https://leetcode-cn.com/problems/hamming-distance/)
```html
Input: x = 1, y = 4
@ -114,7 +116,9 @@ public int hammingDistance(int x, int y) {
# 2. 数组中唯一一个不重复的元素
[136. Single Number (Easy)](https://leetcode.com/problems/single-number/description/)
136\. Single Number (Easy)
[Leetcode](https://leetcode.com/problems/single-number/description/) / [力扣](https://leetcode-cn.com/problems/single-number/description/)
```html
Input: [4,1,2,1,2]
@ -133,7 +137,9 @@ public int singleNumber(int[] nums) {
# 3. 找出数组中缺失的那个数
[268. Missing Number (Easy)](https://leetcode.com/problems/missing-number/description/)
268\. Missing Number (Easy)
[Leetcode](https://leetcode.com/problems/missing-number/description/) / [力扣](https://leetcode-cn.com/problems/missing-number/description/)
```html
Input: [3,0,1]
@ -154,7 +160,9 @@ public int missingNumber(int[] nums) {
# 4. 数组中不重复的两个元素
[260. Single Number III (Medium)](https://leetcode.com/problems/single-number-iii/description/)
260\. Single Number III (Medium)
[Leetcode](https://leetcode.com/problems/single-number-iii/description/) / [力扣](https://leetcode-cn.com/problems/single-number-iii/description/)
两个不相等的元素在位级表示上必定会有一位存在不同。
@ -178,7 +186,9 @@ public int[] singleNumber(int[] nums) {
# 5. 翻转一个数的比特位
[190. Reverse Bits (Easy)](https://leetcode.com/problems/reverse-bits/description/)
190\. Reverse Bits (Easy)
[Leetcode](https://leetcode.com/problems/reverse-bits/description/) / [力扣](https://leetcode-cn.com/problems/reverse-bits/description/)
```java
public int reverseBits(int n) {
@ -233,7 +243,9 @@ a = a ^ b;
# 7. 判断一个数是不是 2 的 n 次方
[231. Power of Two (Easy)](https://leetcode.com/problems/power-of-two/description/)
231\. Power of Two (Easy)
[Leetcode](https://leetcode.com/problems/power-of-two/description/) / [力扣](https://leetcode-cn.com/problems/power-of-two/description/)
二进制表示只有一个 1 存在。
@ -253,7 +265,9 @@ public boolean isPowerOfTwo(int n) {
# 8. 判断一个数是不是 4 的 n 次方
[342. Power of Four (Easy)](https://leetcode.com/problems/power-of-four/)
342\. Power of Four (Easy)
[Leetcode](https://leetcode.com/problems/power-of-four/) / [力扣](https://leetcode-cn.com/problems/power-of-four/)
这种数在二进制表示中有且只有一个奇数位为 1，例如 16（10000）。
@ -273,7 +287,9 @@ public boolean isPowerOfFour(int num) {
# 9. 判断一个数的位级表示是否不会出现连续的 0 和 1
[693. Binary Number with Alternating Bits (Easy)](https://leetcode.com/problems/binary-number-with-alternating-bits/description/)
693\. Binary Number with Alternating Bits (Easy)
[Leetcode](https://leetcode.com/problems/binary-number-with-alternating-bits/description/) / [力扣](https://leetcode-cn.com/problems/binary-number-with-alternating-bits/description/)
```html
Input: 10
@ -298,7 +314,9 @@ public boolean hasAlternatingBits(int n) {
# 10. 求一个数的补码
[476. Number Complement (Easy)](https://leetcode.com/problems/number-complement/description/)
476\. Number Complement (Easy)
[Leetcode](https://leetcode.com/problems/number-complement/description/) / [力扣](https://leetcode-cn.com/problems/number-complement/description/)
```html
Input: 5
@ -353,7 +371,9 @@ public int findComplement(int num) {
# 11. 实现整数的加法
[371. Sum of Two Integers (Easy)](https://leetcode.com/problems/sum-of-two-integers/description/)
371\. Sum of Two Integers (Easy)
[Leetcode](https://leetcode.com/problems/sum-of-two-integers/description/) / [力扣](https://leetcode-cn.com/problems/sum-of-two-integers/description/)
a ^ b 表示没有考虑进位的情况下两数的和，(a & b) << 1 就是进位。
@ -367,7 +387,9 @@ public int getSum(int a, int b) {
# 12. 字符串数组最大乘积
[318. Maximum Product of Word Lengths (Medium)](https://leetcode.com/problems/maximum-product-of-word-lengths/description/)
318\. Maximum Product of Word Lengths (Medium)
[Leetcode](https://leetcode.com/problems/maximum-product-of-word-lengths/description/) / [力扣](https://leetcode-cn.com/problems/maximum-product-of-word-lengths/description/)
```html
Given ["abcw", "baz", "foo", "bar", "xtfn", "abcdef"]
@ -402,7 +424,9 @@ public int maxProduct(String[] words) {
# 13. 统计从 0 \~ n 每个数的二进制表示中 1 的个数
[338. Counting Bits (Medium)](https://leetcode.com/problems/counting-bits/description/)
338\. Counting Bits (Medium)
[Leetcode](https://leetcode.com/problems/counting-bits/description/) / [力扣](https://leetcode-cn.com/problems/counting-bits/description/)
对于数字 6(110)，它可以看成是 4(100) 再加一个 2(10)，因此 dp[i] = dp[i&(i-1)] + 1;

8
docs/notes/Leetcode 题解 - 分治.md
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@ -6,7 +6,9 @@
# 1. 给表达式加括号
[241. Different Ways to Add Parentheses (Medium)](https://leetcode.com/problems/different-ways-to-add-parentheses/description/)
241\. Different Ways to Add Parentheses (Medium)
[Leetcode](https://leetcode.com/problems/different-ways-to-add-parentheses/description/) / [力扣](https://leetcode-cn.com/problems/different-ways-to-add-parentheses/description/)
```html
Input: "2-1-1".
@ -51,7 +53,9 @@ public List<Integer> diffWaysToCompute(String input) {
# 2. 不同的二叉搜索树
[95. Unique Binary Search Trees II (Medium)](https://leetcode.com/problems/unique-binary-search-trees-ii/description/)
95\. Unique Binary Search Trees II (Medium)
[Leetcode](https://leetcode.com/problems/unique-binary-search-trees-ii/description/) / [力扣](https://leetcode-cn.com/problems/unique-binary-search-trees-ii/description/)
给定一个数字 n，要求生成所有值为 1...n 的二叉搜索树。

108
docs/notes/Leetcode 题解 - 动态规划.md
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@ -46,7 +46,9 @@
## 1. 爬楼梯
[70. Climbing Stairs (Easy)](https://leetcode.com/problems/climbing-stairs/description/)
70\. Climbing Stairs (Easy)
[Leetcode](https://leetcode.com/problems/climbing-stairs/description/) / [力扣](https://leetcode-cn.com/problems/climbing-stairs/description/)
题目描述：有 N 阶楼梯，每次可以上一阶或者两阶，求有多少种上楼梯的方法。
@ -77,7 +79,9 @@ public int climbStairs(int n) {
## 2. 强盗抢劫
[198. House Robber (Easy)](https://leetcode.com/problems/house-robber/description/)
198\. House Robber (Easy)
[Leetcode](https://leetcode.com/problems/house-robber/description/) / [力扣](https://leetcode-cn.com/problems/house-robber/description/)
题目描述：抢劫一排住户，但是不能抢邻近的住户，求最大抢劫量。
@ -103,7 +107,9 @@ public int rob(int[] nums) {
## 3. 强盗在环形街区抢劫
[213. House Robber II (Medium)](https://leetcode.com/problems/house-robber-ii/description/)
213\. House Robber II (Medium)
[Leetcode](https://leetcode.com/problems/house-robber-ii/description/) / [力扣](https://leetcode-cn.com/problems/house-robber-ii/description/)
```java
public int rob(int[] nums) {
@ -159,7 +165,9 @@ private int rob(int[] nums, int first, int last) {
## 1. 矩阵的最小路径和
[64. Minimum Path Sum (Medium)](https://leetcode.com/problems/minimum-path-sum/description/)
64\. Minimum Path Sum (Medium)
[Leetcode](https://leetcode.com/problems/minimum-path-sum/description/) / [力扣](https://leetcode-cn.com/problems/minimum-path-sum/description/)
```html
[[1,3,1],
@ -195,7 +203,9 @@ public int minPathSum(int[][] grid) {
## 2. 矩阵的总路径数
[62. Unique Paths (Medium)](https://leetcode.com/problems/unique-paths/description/)
62\. Unique Paths (Medium)
[Leetcode](https://leetcode.com/problems/unique-paths/description/) / [力扣](https://leetcode-cn.com/problems/unique-paths/description/)
题目描述：统计从矩阵左上角到右下角的路径总数，每次只能向右或者向下移动。
@ -232,7 +242,9 @@ public int uniquePaths(int m, int n) {
## 1. 数组区间和
[303. Range Sum Query - Immutable (Easy)](https://leetcode.com/problems/range-sum-query-immutable/description/)
303\. Range Sum Query - Immutable (Easy)
[Leetcode](https://leetcode.com/problems/range-sum-query-immutable/description/) / [力扣](https://leetcode-cn.com/problems/range-sum-query-immutable/description/)
```html
Given nums = [-2, 0, 3, -5, 2, -1]
@ -264,7 +276,9 @@ class NumArray {
## 2. 数组中等差递增子区间的个数
[413. Arithmetic Slices (Medium)](https://leetcode.com/problems/arithmetic-slices/description/)
413\. Arithmetic Slices (Medium)
[Leetcode](https://leetcode.com/problems/arithmetic-slices/description/) / [力扣](https://leetcode-cn.com/problems/arithmetic-slices/description/)
```html
A = [0, 1, 2, 3, 4]
@ -323,7 +337,9 @@ public int numberOfArithmeticSlices(int[] A) {
## 1. 分割整数的最大乘积
[343. Integer Break (Medim)](https://leetcode.com/problems/integer-break/description/)
343\. Integer Break (Medim)
[Leetcode](https://leetcode.com/problems/integer-break/description/) / [力扣](https://leetcode-cn.com/problems/integer-break/description/)
题目描述：For example, given n = 2, return 1 (2 = 1 + 1); given n = 10, return 36 (10 = 3 + 3 + 4).
@ -342,7 +358,9 @@ public int integerBreak(int n) {
## 2. 按平方数来分割整数
[279. Perfect Squares(Medium)](https://leetcode.com/problems/perfect-squares/description/)
279\. Perfect Squares(Medium)
[Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/)
题目描述：For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.
@ -378,7 +396,9 @@ private List<Integer> generateSquareList(int n) {
## 3. 分割整数构成字母字符串
[91. Decode Ways (Medium)](https://leetcode.com/problems/decode-ways/description/)
91\. Decode Ways (Medium)
[Leetcode](https://leetcode.com/problems/decode-ways/description/) / [力扣](https://leetcode-cn.com/problems/decode-ways/description/)
题目描述：Given encoded message "12", it could be decoded as "AB" (1 2) or "L" (12).
@ -426,7 +446,9 @@ public int numDecodings(String s) {
## 1. 最长递增子序列
[300. Longest Increasing Subsequence (Medium)](https://leetcode.com/problems/longest-increasing-subsequence/description/)
300\. Longest Increasing Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/longest-increasing-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-increasing-subsequence/description/)
```java
public int lengthOfLIS(int[] nums) {
@ -508,7 +530,9 @@ private int binarySearch(int[] tails, int len, int key) {
## 2. 一组整数对能够构成的最长链
[646. Maximum Length of Pair Chain (Medium)](https://leetcode.com/problems/maximum-length-of-pair-chain/description/)
646\. Maximum Length of Pair Chain (Medium)
[Leetcode](https://leetcode.com/problems/maximum-length-of-pair-chain/description/) / [力扣](https://leetcode-cn.com/problems/maximum-length-of-pair-chain/description/)
```html
Input: [[1,2], [2,3], [3,4]]
@ -540,7 +564,9 @@ public int findLongestChain(int[][] pairs) {
## 3. 最长摆动子序列
[376. Wiggle Subsequence (Medium)](https://leetcode.com/problems/wiggle-subsequence/description/)
376\. Wiggle Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/wiggle-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/wiggle-subsequence/description/)
```html
Input: [1,7,4,9,2,5]
@ -697,7 +723,9 @@ public int knapsack(int W, int N, int[] weights, int[] values) {
## 1. 划分数组为和相等的两部分
[416. Partition Equal Subset Sum (Medium)](https://leetcode.com/problems/partition-equal-subset-sum/description/)
416\. Partition Equal Subset Sum (Medium)
[Leetcode](https://leetcode.com/problems/partition-equal-subset-sum/description/) / [力扣](https://leetcode-cn.com/problems/partition-equal-subset-sum/description/)
```html
Input: [1, 5, 11, 5]
@ -737,7 +765,9 @@ private int computeArraySum(int[] nums) {
## 2. 改变一组数的正负号使得它们的和为一给定数
[494. Target Sum (Medium)](https://leetcode.com/problems/target-sum/description/)
494\. Target Sum (Medium)
[Leetcode](https://leetcode.com/problems/target-sum/description/) / [力扣](https://leetcode-cn.com/problems/target-sum/description/)
```html
Input: nums is [1, 1, 1, 1, 1], S is 3.
@ -809,7 +839,9 @@ private int findTargetSumWays(int[] nums, int start, int S) {
## 3. 01 字符构成最多的字符串
[474. Ones and Zeroes (Medium)](https://leetcode.com/problems/ones-and-zeroes/description/)
474\. Ones and Zeroes (Medium)
[Leetcode](https://leetcode.com/problems/ones-and-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/ones-and-zeroes/description/)
```html
Input: Array = {"10", "0001", "111001", "1", "0"}, m = 5, n = 3
@ -847,7 +879,9 @@ public int findMaxForm(String[] strs, int m, int n) {
## 4. 找零钱的最少硬币数
[322. Coin Change (Medium)](https://leetcode.com/problems/coin-change/description/)
322\. Coin Change (Medium)
[Leetcode](https://leetcode.com/problems/coin-change/description/) / [力扣](https://leetcode-cn.com/problems/coin-change/description/)
```html
Example 1:
@ -888,7 +922,9 @@ public int coinChange(int[] coins, int amount) {
## 5. 找零钱的硬币数组合
[518\. Coin Change 2 (Medium)](https://leetcode.com/problems/coin-change-2/description/)
518\. Coin Change 2 (Medium)
[Leetcode](https://leetcode.com/problems/coin-change-2/description/) / [力扣](https://leetcode-cn.com/problems/coin-change-2/description/)
```text-html-basic
Input: amount = 5, coins = [1, 2, 5]
@ -920,7 +956,9 @@ public int change(int amount, int[] coins) {
## 6. 字符串按单词列表分割
[139. Word Break (Medium)](https://leetcode.com/problems/word-break/description/)
139\. Word Break (Medium)
[Leetcode](https://leetcode.com/problems/word-break/description/) / [力扣](https://leetcode-cn.com/problems/word-break/description/)
```html
s = "leetcode",
@ -957,7 +995,9 @@ public boolean wordBreak(String s, List<String> wordDict) {
## 7. 组合总和
[377. Combination Sum IV (Medium)](https://leetcode.com/problems/combination-sum-iv/description/)
377\. Combination Sum IV (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-iv/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iv/description/)
```html
nums = [1, 2, 3]
@ -1000,7 +1040,9 @@ public int combinationSum4(int[] nums, int target) {
## 1. 需要冷却期的股票交易
[309. Best Time to Buy and Sell Stock with Cooldown(Medium)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/)
309\. Best Time to Buy and Sell Stock with Cooldown(Medium)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/)
题目描述：交易之后需要有一天的冷却时间。
@ -1030,7 +1072,9 @@ public int maxProfit(int[] prices) {
## 2. 需要交易费用的股票交易
[714. Best Time to Buy and Sell Stock with Transaction Fee (Medium)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/)
714\. Best Time to Buy and Sell Stock with Transaction Fee (Medium)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/)
```html
Input: prices = [1, 3, 2, 8, 4, 9], fee = 2
@ -1069,7 +1113,9 @@ public int maxProfit(int[] prices, int fee) {
## 3. 只能进行两次的股票交易
[123. Best Time to Buy and Sell Stock III (Hard)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/description/)
123\. Best Time to Buy and Sell Stock III (Hard)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iii/description/)
```java
public int maxProfit(int[] prices) {
@ -1095,7 +1141,9 @@ public int maxProfit(int[] prices) {
## 4. 只能进行 k 次的股票交易
[188. Best Time to Buy and Sell Stock IV (Hard)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/description/)
188\. Best Time to Buy and Sell Stock IV (Hard)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iv/description/)
```java
public int maxProfit(int k, int[] prices) {
@ -1125,7 +1173,9 @@ public int maxProfit(int k, int[] prices) {
## 1. 删除两个字符串的字符使它们相等
[583. Delete Operation for Two Strings (Medium)](https://leetcode.com/problems/delete-operation-for-two-strings/description/)
583\. Delete Operation for Two Strings (Medium)
[Leetcode](https://leetcode.com/problems/delete-operation-for-two-strings/description/) / [力扣](https://leetcode-cn.com/problems/delete-operation-for-two-strings/description/)
```html
Input: "sea", "eat"
@ -1154,7 +1204,9 @@ public int minDistance(String word1, String word2) {
## 2. 编辑距离
[72. Edit Distance (Hard)](https://leetcode.com/problems/edit-distance/description/)
72\. Edit Distance (Hard)
[Leetcode](https://leetcode.com/problems/edit-distance/description/) / [力扣](https://leetcode-cn.com/problems/edit-distance/description/)
```html
Example 1:
@ -1207,7 +1259,9 @@ public int minDistance(String word1, String word2) {
## 3. 复制粘贴字符
[650. 2 Keys Keyboard (Medium)](https://leetcode.com/problems/2-keys-keyboard/description/)
650\. 2 Keys Keyboard (Medium)
[Leetcode](https://leetcode.com/problems/2-keys-keyboard/description/) / [力扣](https://leetcode-cn.com/problems/2-keys-keyboard/description/)
题目描述：最开始只有一个字符 A，问需要多少次操作能够得到 n 个字符 A，每次操作可以复制当前所有的字符，或者粘贴。

20
docs/notes/Leetcode 题解 - 哈希表.md
View File

@ -10,12 +10,16 @@
- Java 中的 **HashSet** 用于存储一个集合，可以查找元素是否在集合中。如果元素有穷，并且范围不大，那么可以用一个布尔数组来存储一个元素是否存在。例如对于只有小写字符的元素，就可以用一个长度为 26 的布尔数组来存储一个字符集合，使得空间复杂度降低为 O(1)。
- Java 中的 **HashMap** 主要用于映射关系，从而把两个元素联系起来。HashMap 也可以用来对元素进行计数统计，此时键为元素，值为计数。和 HashSet 类似，如果元素有穷并且范围不大，可以用整型数组来进行统计。在对一个内容进行压缩或者其它转换时，利用 HashMap 可以把原始内容和转换后的内容联系起来。例如在一个简化 url 的系统中 [Leetcdoe : 535. Encode and Decode TinyURL (Medium)](https://leetcode.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源。
Java 中的 **HashMap** 主要用于映射关系，从而把两个元素联系起来。HashMap 也可以用来对元素进行计数统计，此时键为元素，值为计数。和 HashSet 类似，如果元素有穷并且范围不大，可以用整型数组来进行统计。在对一个内容进行压缩或者其它转换时，利用 HashMap 可以把原始内容和转换后的内容联系起来。例如在一个简化 url 的系统中 [Leetcdoe : 535. Encode and Decode TinyURL (Medium)
[Leetcode](https://leetcode.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源<EFBFBD>)
# 1. 数组中两个数的和为给定值
[1. Two Sum (Easy)](https://leetcode.com/problems/two-sum/description/)
1\. Two Sum (Easy)
[Leetcode](https://leetcode.com/problems/two-sum/description/) / [力扣](https://leetcode-cn.com/problems/two-sum/description/)
可以先对数组进行排序，然后使用双指针方法或者二分查找方法。这样做的时间复杂度为 O(NlogN)，空间复杂度为 O(1)。
@ -37,7 +41,9 @@ public int[] twoSum(int[] nums, int target) {
# 2. 判断数组是否含有重复元素
[217. Contains Duplicate (Easy)](https://leetcode.com/problems/contains-duplicate/description/)
217\. Contains Duplicate (Easy)
[Leetcode](https://leetcode.com/problems/contains-duplicate/description/) / [力扣](https://leetcode-cn.com/problems/contains-duplicate/description/)
```java
public boolean containsDuplicate(int[] nums) {
@ -51,7 +57,9 @@ public boolean containsDuplicate(int[] nums) {
# 3. 最长和谐序列
[594. Longest Harmonious Subsequence (Easy)](https://leetcode.com/problems/longest-harmonious-subsequence/description/)
594\. Longest Harmonious Subsequence (Easy)
[Leetcode](https://leetcode.com/problems/longest-harmonious-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-harmonious-subsequence/description/)
```html
Input: [1,3,2,2,5,2,3,7]
@ -79,7 +87,9 @@ public int findLHS(int[] nums) {
# 4. 最长连续序列
[128. Longest Consecutive Sequence (Hard)](https://leetcode.com/problems/longest-consecutive-sequence/description/)
128\. Longest Consecutive Sequence (Hard)
[Leetcode](https://leetcode.com/problems/longest-consecutive-sequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-consecutive-sequence/description/)
```html
Given [100, 4, 200, 1, 3, 2],

16
docs/notes/Leetcode 题解 - 图.md
View File

@ -15,7 +15,9 @@
## 1. 判断是否为二分图
[785. Is Graph Bipartite? (Medium)](https://leetcode.com/problems/is-graph-bipartite/description/)
785\. Is Graph Bipartite? (Medium)
[Leetcode](https://leetcode.com/problems/is-graph-bipartite/description/) / [力扣](https://leetcode-cn.com/problems/is-graph-bipartite/description/)
```html
Input: [[1,3], [0,2], [1,3], [0,2]]
@ -74,7 +76,9 @@ private boolean isBipartite(int curNode, int curColor, int[] colors, int[][] gra
## 1. 课程安排的合法性
[207. Course Schedule (Medium)](https://leetcode.com/problems/course-schedule/description/)
207\. Course Schedule (Medium)
[Leetcode](https://leetcode.com/problems/course-schedule/description/) / [力扣](https://leetcode-cn.com/problems/course-schedule/description/)
```html
2, [[1,0]]
@ -132,7 +136,9 @@ private boolean hasCycle(boolean[] globalMarked, boolean[] localMarked,
## 2. 课程安排的顺序
[210. Course Schedule II (Medium)](https://leetcode.com/problems/course-schedule-ii/description/)
210\. Course Schedule II (Medium)
[Leetcode](https://leetcode.com/problems/course-schedule-ii/description/) / [力扣](https://leetcode-cn.com/problems/course-schedule-ii/description/)
```html
4, [[1,0],[2,0],[3,1],[3,2]]
@ -195,7 +201,9 @@ private boolean hasCycle(boolean[] globalMarked, boolean[] localMarked, List<Int
## 1. 冗余连接
[684. Redundant Connection (Medium)](https://leetcode.com/problems/redundant-connection/description/)
684\. Redundant Connection (Medium)
[Leetcode](https://leetcode.com/problems/redundant-connection/description/) / [力扣](https://leetcode-cn.com/problems/redundant-connection/description/)
```html
Input: [[1,2], [1,3], [2,3]]

24
docs/notes/Leetcode 题解 - 字符串.md
View File

@ -50,7 +50,9 @@ Return "student a am I"
# 4. 两个字符串包含的字符是否完全相同
[242. Valid Anagram (Easy)](https://leetcode.com/problems/valid-anagram/description/)
242\. Valid Anagram (Easy)
[Leetcode](https://leetcode.com/problems/valid-anagram/description/) / [力扣](https://leetcode-cn.com/problems/valid-anagram/description/)
```html
s = "anagram", t = "nagaram", return true.
@ -81,7 +83,9 @@ public boolean isAnagram(String s, String t) {
# 5. 计算一组字符集合可以组成的回文字符串的最大长度
[409. Longest Palindrome (Easy)](https://leetcode.com/problems/longest-palindrome/description/)
409\. Longest Palindrome (Easy)
[Leetcode](https://leetcode.com/problems/longest-palindrome/description/) / [力扣](https://leetcode-cn.com/problems/longest-palindrome/description/)
```html
Input : "abccccdd"
@ -112,7 +116,9 @@ public int longestPalindrome(String s) {
# 6. 字符串同构
[205. Isomorphic Strings (Easy)](https://leetcode.com/problems/isomorphic-strings/description/)
205\. Isomorphic Strings (Easy)
[Leetcode](https://leetcode.com/problems/isomorphic-strings/description/) / [力扣](https://leetcode-cn.com/problems/isomorphic-strings/description/)
```html
Given "egg", "add", return true.
@ -140,7 +146,9 @@ public boolean isIsomorphic(String s, String t) {
# 7. 回文子字符串个数
[647. Palindromic Substrings (Medium)](https://leetcode.com/problems/palindromic-substrings/description/)
647\. Palindromic Substrings (Medium)
[Leetcode](https://leetcode.com/problems/palindromic-substrings/description/) / [力扣](https://leetcode-cn.com/problems/palindromic-substrings/description/)
```html
Input: "aaa"
@ -172,7 +180,9 @@ private void extendSubstrings(String s, int start, int end) {
# 8. 判断一个整数是否是回文数
[9. Palindrome Number (Easy)](https://leetcode.com/problems/palindrome-number/description/)
9\. Palindrome Number (Easy)
[Leetcode](https://leetcode.com/problems/palindrome-number/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-number/description/)
要求不能使用额外空间，也就不能将整数转换为字符串进行判断。
@ -197,7 +207,9 @@ public boolean isPalindrome(int x) {
# 9. 统计二进制字符串中连续 1 和连续 0 数量相同的子字符串个数
[696. Count Binary Substrings (Easy)](https://leetcode.com/problems/count-binary-substrings/description/)
696\. Count Binary Substrings (Easy)
[Leetcode](https://leetcode.com/problems/count-binary-substrings/description/) / [力扣](https://leetcode-cn.com/problems/count-binary-substrings/description/)
```html
Input: "00110011"

16
docs/notes/Leetcode 题解 - 排序.md
View File

@ -28,7 +28,9 @@
## 1. Kth Element
[215. Kth Largest Element in an Array (Medium)](https://leetcode.com/problems/kth-largest-element-in-an-array/description/)
215\. Kth Largest Element in an Array (Medium)
[Leetcode](https://leetcode.com/problems/kth-largest-element-in-an-array/description/) / [力扣](https://leetcode-cn.com/problems/kth-largest-element-in-an-array/description/)
```text
Input: [3,2,1,5,6,4] and k = 2
@ -104,7 +106,9 @@ private void swap(int[] a, int i, int j) {
## 1. 出现频率最多的 k 个元素
[347. Top K Frequent Elements (Medium)](https://leetcode.com/problems/top-k-frequent-elements/description/)
347\. Top K Frequent Elements (Medium)
[Leetcode](https://leetcode.com/problems/top-k-frequent-elements/description/) / [力扣](https://leetcode-cn.com/problems/top-k-frequent-elements/description/)
```html
Given [1,1,1,2,2,3] and k = 2, return [1,2].
@ -145,7 +149,9 @@ public List<Integer> topKFrequent(int[] nums, int k) {
## 2. 按照字符出现次数对字符串排序
[451. Sort Characters By Frequency (Medium)](https://leetcode.com/problems/sort-characters-by-frequency/description/)
451\. Sort Characters By Frequency (Medium)
[Leetcode](https://leetcode.com/problems/sort-characters-by-frequency/description/) / [力扣](https://leetcode-cn.com/problems/sort-characters-by-frequency/description/)
```html
Input:
@ -199,7 +205,9 @@ public String frequencySort(String s) {
## 1. 按颜色进行排序
[75. Sort Colors (Medium)](https://leetcode.com/problems/sort-colors/description/)
75\. Sort Colors (Medium)
[Leetcode](https://leetcode.com/problems/sort-colors/description/) / [力扣](https://leetcode-cn.com/problems/sort-colors/description/)
```html
Input: [2,0,2,1,1,0]

92
docs/notes/Leetcode 题解 - 搜索.md
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@ -61,7 +61,9 @@
## 1. 计算在网格中从原点到特定点的最短路径长度
[1091. Shortest Path in Binary Matrix(Medium)](https://leetcode.com/problems/shortest-path-in-binary-matrix/)
1091\. Shortest Path in Binary Matrix(Medium)
[Leetcode](https://leetcode.com/problems/shortest-path-in-binary-matrix/) / [力扣](https://leetcode-cn.com/problems/shortest-path-in-binary-matrix/)
```html
[[1,1,0,1],
@ -104,7 +106,9 @@ public int shortestPathBinaryMatrix(int[][] grids) {
## 2. 组成整数的最小平方数数量
[279. Perfect Squares (Medium)](https://leetcode.com/problems/perfect-squares/description/)
279\. Perfect Squares (Medium)
[Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/)
```html
For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.
@ -167,7 +171,9 @@ private List<Integer> generateSquares(int n) {
## 3. 最短单词路径
[127. Word Ladder (Medium)](https://leetcode.com/problems/word-ladder/description/)
127\. Word Ladder (Medium)
[Leetcode](https://leetcode.com/problems/word-ladder/description/) / [力扣](https://leetcode-cn.com/problems/word-ladder/description/)
```html
Input:
@ -278,7 +284,9 @@ private int getShortestPath(List<Integer>[] graphic, int start, int end) {
## 1. 查找最大的连通面积
[695. Max Area of Island (Medium)](https://leetcode.com/problems/max-area-of-island/description/)
695\. Max Area of Island (Medium)
[Leetcode](https://leetcode.com/problems/max-area-of-island/description/) / [力扣](https://leetcode-cn.com/problems/max-area-of-island/description/)
```html
[[0,0,1,0,0,0,0,1,0,0,0,0,0],
@ -325,7 +333,9 @@ private int dfs(int[][] grid, int r, int c) {
## 2. 矩阵中的连通分量数目
[200. Number of Islands (Medium)](https://leetcode.com/problems/number-of-islands/description/)
200\. Number of Islands (Medium)
[Leetcode](https://leetcode.com/problems/number-of-islands/description/) / [力扣](https://leetcode-cn.com/problems/number-of-islands/description/)
```html
Input:
@ -374,7 +384,9 @@ private void dfs(char[][] grid, int i, int j) {
## 3. 好友关系的连通分量数目
[547. Friend Circles (Medium)](https://leetcode.com/problems/friend-circles/description/)
547\. Friend Circles (Medium)
[Leetcode](https://leetcode.com/problems/friend-circles/description/) / [力扣](https://leetcode-cn.com/problems/friend-circles/description/)
```html
Input:
@ -418,7 +430,9 @@ private void dfs(int[][] M, int i, boolean[] hasVisited) {
## 4. 填充封闭区域
[130. Surrounded Regions (Medium)](https://leetcode.com/problems/surrounded-regions/description/)
130\. Surrounded Regions (Medium)
[Leetcode](https://leetcode.com/problems/surrounded-regions/description/) / [力扣](https://leetcode-cn.com/problems/surrounded-regions/description/)
```html
For example,
@ -483,7 +497,9 @@ private void dfs(char[][] board, int r, int c) {
## 5. 能到达的太平洋和大西洋的区域
[417. Pacific Atlantic Water Flow (Medium)](https://leetcode.com/problems/pacific-atlantic-water-flow/description/)
417\. Pacific Atlantic Water Flow (Medium)
[Leetcode](https://leetcode.com/problems/pacific-atlantic-water-flow/description/) / [力扣](https://leetcode-cn.com/problems/pacific-atlantic-water-flow/description/)
```html
Given the following 5x5 matrix:
@ -571,7 +587,9 @@ Backtracking（回溯）属于 DFS。
## 1. 数字键盘组合
[17. Letter Combinations of a Phone Number (Medium)](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/)
17\. Letter Combinations of a Phone Number (Medium)
[Leetcode](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/) / [力扣](https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/description/)
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/9823768c-212b-4b1a-b69a-b3f59e07b977.jpg"/> </div><br>
@ -609,7 +627,9 @@ private void doCombination(StringBuilder prefix, List<String> combinations, fina
## 2. IP 地址划分
[93. Restore IP Addresses(Medium)](https://leetcode.com/problems/restore-ip-addresses/description/)
93\. Restore IP Addresses(Medium)
[Leetcode](https://leetcode.com/problems/restore-ip-addresses/description/) / [力扣](https://leetcode-cn.com/problems/restore-ip-addresses/description/)
```html
Given "25525511135",
@ -650,7 +670,9 @@ private void doRestore(int k, StringBuilder tempAddress, List<String> addresses,
## 3. 在矩阵中寻找字符串
[79. Word Search (Medium)](https://leetcode.com/problems/word-search/description/)
79\. Word Search (Medium)
[Leetcode](https://leetcode.com/problems/word-search/description/) / [力扣](https://leetcode-cn.com/problems/word-search/description/)
```html
For example,
@ -719,7 +741,9 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina
## 4. 输出二叉树中所有从根到叶子的路径
[257. Binary Tree Paths (Easy)](https://leetcode.com/problems/binary-tree-paths/description/)
257\. Binary Tree Paths (Easy)
[Leetcode](https://leetcode.com/problems/binary-tree-paths/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-paths/description/)
```html
1
@ -777,7 +801,9 @@ private String buildPath(List<Integer> values) {
## 5. 排列
[46. Permutations (Medium)](https://leetcode.com/problems/permutations/description/)
46\. Permutations (Medium)
[Leetcode](https://leetcode.com/problems/permutations/description/) / [力扣](https://leetcode-cn.com/problems/permutations/description/)
```html
[1,2,3] have the following permutations:
@ -820,7 +846,9 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
## 6. 含有相同元素求排列
[47. Permutations II (Medium)](https://leetcode.com/problems/permutations-ii/description/)
47\. Permutations II (Medium)
[Leetcode](https://leetcode.com/problems/permutations-ii/description/) / [力扣](https://leetcode-cn.com/problems/permutations-ii/description/)
```html
[1,1,2] have the following unique permutations:
@ -865,7 +893,9 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
## 7. 组合
[77. Combinations (Medium)](https://leetcode.com/problems/combinations/description/)
77\. Combinations (Medium)
[Leetcode](https://leetcode.com/problems/combinations/description/) / [力扣](https://leetcode-cn.com/problems/combinations/description/)
```html
If n = 4 and k = 2, a solution is:
@ -902,7 +932,9 @@ private void backtracking(List<Integer> combineList, List<List<Integer>> combina
## 8. 组合求和
[39. Combination Sum (Medium)](https://leetcode.com/problems/combination-sum/description/)
39\. Combination Sum (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum/description/)
```html
given candidate set [2, 3, 6, 7] and target 7,
@ -936,7 +968,9 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
## 9. 含有相同元素的组合求和
[40. Combination Sum II (Medium)](https://leetcode.com/problems/combination-sum-ii/description/)
40\. Combination Sum II (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-ii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-ii/description/)
```html
For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8,
@ -981,7 +1015,9 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
## 10. 1-9 数字的组合求和
[216. Combination Sum III (Medium)](https://leetcode.com/problems/combination-sum-iii/description/)
216\. Combination Sum III (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iii/description/)
```html
Input: k = 3, n = 9
@ -1021,7 +1057,9 @@ private void backtracking(int k, int n, int start,
## 11. 子集
[78. Subsets (Medium)](https://leetcode.com/problems/subsets/description/)
78\. Subsets (Medium)
[Leetcode](https://leetcode.com/problems/subsets/description/) / [力扣](https://leetcode-cn.com/problems/subsets/description/)
找出集合的所有子集，子集不能重复，[1, 2] 和 [2, 1] 这种子集算重复
@ -1052,7 +1090,9 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
## 12. 含有相同元素求子集
[90. Subsets II (Medium)](https://leetcode.com/problems/subsets-ii/description/)
90\. Subsets II (Medium)
[Leetcode](https://leetcode.com/problems/subsets-ii/description/) / [力扣](https://leetcode-cn.com/problems/subsets-ii/description/)
```html
For example,
@ -1102,7 +1142,9 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
## 13. 分割字符串使得每个部分都是回文数
[131. Palindrome Partitioning (Medium)](https://leetcode.com/problems/palindrome-partitioning/description/)
131\. Palindrome Partitioning (Medium)
[Leetcode](https://leetcode.com/problems/palindrome-partitioning/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-partitioning/description/)
```html
For example, given s = "aab",
@ -1148,7 +1190,9 @@ private boolean isPalindrome(String s, int begin, int end) {
## 14. 数独
[37. Sudoku Solver (Hard)](https://leetcode.com/problems/sudoku-solver/description/)
37\. Sudoku Solver (Hard)
[Leetcode](https://leetcode.com/problems/sudoku-solver/description/) / [力扣](https://leetcode-cn.com/problems/sudoku-solver/description/)
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/0e8fdc96-83c1-4798-9abe-45fc91d70b9d.png"/> </div><br>
@ -1205,7 +1249,9 @@ private int cubeNum(int i, int j) {
## 15. N 皇后
[51. N-Queens (Hard)](https://leetcode.com/problems/n-queens/description/)
51\. N-Queens (Hard)
[Leetcode](https://leetcode.com/problems/n-queens/description/) / [力扣](https://leetcode-cn.com/problems/n-queens/description/)
<div align="center"> <img src="https://cs-notes-1256109796.cos.ap-guangzhou.myqcloud.com/067b310c-6877-40fe-9dcf-10654e737485.jpg"/> </div><br>

52
docs/notes/Leetcode 题解 - 数学.md
View File

@ -46,7 +46,9 @@ x 和 y 的最小公倍数为：lcm(x,y) = 2<sup>max(m0,n0)</sup> \* 3<sup>max(
## 1. 生成素数序列
[204. Count Primes (Easy)](https://leetcode.com/problems/count-primes/description/)
204\. Count Primes (Easy)
[Leetcode](https://leetcode.com/problems/count-primes/description/) / [力扣](https://leetcode-cn.com/problems/count-primes/description/)
埃拉托斯特尼筛法在每次找到一个素数时，将能被素数整除的数排除掉。
@ -122,7 +124,9 @@ public int gcd(int a, int b) {
## 1. 7 进制
[504. Base 7 (Easy)](https://leetcode.com/problems/base-7/description/)
504\. Base 7 (Easy)
[Leetcode](https://leetcode.com/problems/base-7/description/) / [力扣](https://leetcode-cn.com/problems/base-7/description/)
```java
public String convertToBase7(int num) {
@ -153,7 +157,9 @@ public String convertToBase7(int num) {
## 2. 16 进制
[405. Convert a Number to Hexadecimal (Easy)](https://leetcode.com/problems/convert-a-number-to-hexadecimal/description/)
405\. Convert a Number to Hexadecimal (Easy)
[Leetcode](https://leetcode.com/problems/convert-a-number-to-hexadecimal/description/) / [力扣](https://leetcode-cn.com/problems/convert-a-number-to-hexadecimal/description/)
```html
Input:
@ -186,7 +192,9 @@ public String toHex(int num) {
## 3. 26 进制
[168. Excel Sheet Column Title (Easy)](https://leetcode.com/problems/excel-sheet-column-title/description/)
168\. Excel Sheet Column Title (Easy)
[Leetcode](https://leetcode.com/problems/excel-sheet-column-title/description/) / [力扣](https://leetcode-cn.com/problems/excel-sheet-column-title/description/)
```html
1 -> A
@ -214,7 +222,9 @@ public String convertToTitle(int n) {
## 1. 统计阶乘尾部有多少个 0
[172. Factorial Trailing Zeroes (Easy)](https://leetcode.com/problems/factorial-trailing-zeroes/description/)
172\. Factorial Trailing Zeroes (Easy)
[Leetcode](https://leetcode.com/problems/factorial-trailing-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/factorial-trailing-zeroes/description/)
尾部的 0 由 2 * 5 得来，2 的数量明显多于 5 的数量，因此只要统计有多少个 5 即可。
@ -232,7 +242,9 @@ public int trailingZeroes(int n) {
## 1. 二进制加法
[67. Add Binary (Easy)](https://leetcode.com/problems/add-binary/description/)
67\. Add Binary (Easy)
[Leetcode](https://leetcode.com/problems/add-binary/description/) / [力扣](https://leetcode-cn.com/problems/add-binary/description/)
```html
a = "11"
@ -260,7 +272,9 @@ public String addBinary(String a, String b) {
## 2. 字符串加法
[415. Add Strings (Easy)](https://leetcode.com/problems/add-strings/description/)
415\. Add Strings (Easy)
[Leetcode](https://leetcode.com/problems/add-strings/description/) / [力扣](https://leetcode-cn.com/problems/add-strings/description/)
字符串的值为非负整数。
@ -282,7 +296,9 @@ public String addStrings(String num1, String num2) {
## 1. 改变数组元素使所有的数组元素都相等
[462. Minimum Moves to Equal Array Elements II (Medium)](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/description/)
462\. Minimum Moves to Equal Array Elements II (Medium)
[Leetcode](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/description/) / [力扣](https://leetcode-cn.com/problems/minimum-moves-to-equal-array-elements-ii/description/)
```html
Input:
@ -378,7 +394,9 @@ private void swap(int[] nums, int i, int j) {
## 1. 数组中出现次数多于 n / 2 的元素
[169. Majority Element (Easy)](https://leetcode.com/problems/majority-element/description/)
169\. Majority Element (Easy)
[Leetcode](https://leetcode.com/problems/majority-element/description/) / [力扣](https://leetcode-cn.com/problems/majority-element/description/)
先对数组排序，最中间那个数出现次数一定多于 n / 2。
@ -406,7 +424,9 @@ public int majorityElement(int[] nums) {
## 1. 平方数
[367. Valid Perfect Square (Easy)](https://leetcode.com/problems/valid-perfect-square/description/)
367\. Valid Perfect Square (Easy)
[Leetcode](https://leetcode.com/problems/valid-perfect-square/description/) / [力扣](https://leetcode-cn.com/problems/valid-perfect-square/description/)
```html
Input: 16
@ -432,7 +452,9 @@ public boolean isPerfectSquare(int num) {
## 2. 3 的 n 次方
[326. Power of Three (Easy)](https://leetcode.com/problems/power-of-three/description/)
326\. Power of Three (Easy)
[Leetcode](https://leetcode.com/problems/power-of-three/description/) / [力扣](https://leetcode-cn.com/problems/power-of-three/description/)
```java
public boolean isPowerOfThree(int n) {
@ -442,7 +464,9 @@ public boolean isPowerOfThree(int n) {
## 3. 乘积数组
[238. Product of Array Except Self (Medium)](https://leetcode.com/problems/product-of-array-except-self/description/)
238\. Product of Array Except Self (Medium)
[Leetcode](https://leetcode.com/problems/product-of-array-except-self/description/) / [力扣](https://leetcode-cn.com/problems/product-of-array-except-self/description/)
```html
For example, given [1,2,3,4], return [24,12,8,6].
@ -473,7 +497,9 @@ public int[] productExceptSelf(int[] nums) {
## 4. 找出数组中的乘积最大的三个数
[628. Maximum Product of Three Numbers (Easy)](https://leetcode.com/problems/maximum-product-of-three-numbers/description/)
628\. Maximum Product of Three Numbers (Easy)
[Leetcode](https://leetcode.com/problems/maximum-product-of-three-numbers/description/) / [力扣](https://leetcode-cn.com/problems/maximum-product-of-three-numbers/description/)
```html
Input: [1,2,3,4]

60
docs/notes/Leetcode 题解 - 数组与矩阵.md
View File

@ -16,7 +16,9 @@
# 1. 把数组中的 0 移到末尾
[283. Move Zeroes (Easy)](https://leetcode.com/problems/move-zeroes/description/)
283\. Move Zeroes (Easy)
[Leetcode](https://leetcode.com/problems/move-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/move-zeroes/description/)
```html
For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0].
@ -38,7 +40,9 @@ public void moveZeroes(int[] nums) {
# 2. 改变矩阵维度
[566. Reshape the Matrix (Easy)](https://leetcode.com/problems/reshape-the-matrix/description/)
566\. Reshape the Matrix (Easy)
[Leetcode](https://leetcode.com/problems/reshape-the-matrix/description/) / [力扣](https://leetcode-cn.com/problems/reshape-the-matrix/description/)
```html
Input:
@ -74,7 +78,9 @@ public int[][] matrixReshape(int[][] nums, int r, int c) {
# 3. 找出数组中最长的连续 1
[485. Max Consecutive Ones (Easy)](https://leetcode.com/problems/max-consecutive-ones/description/)
485\. Max Consecutive Ones (Easy)
[Leetcode](https://leetcode.com/problems/max-consecutive-ones/description/) / [力扣](https://leetcode-cn.com/problems/max-consecutive-ones/description/)
```java
public int findMaxConsecutiveOnes(int[] nums) {
@ -89,7 +95,9 @@ public int findMaxConsecutiveOnes(int[] nums) {
# 4. 有序矩阵查找
[240. Search a 2D Matrix II (Medium)](https://leetcode.com/problems/search-a-2d-matrix-ii/description/)
240\. Search a 2D Matrix II (Medium)
[Leetcode](https://leetcode.com/problems/search-a-2d-matrix-ii/description/) / [力扣](https://leetcode-cn.com/problems/search-a-2d-matrix-ii/description/)
```html
[
@ -115,7 +123,9 @@ public boolean searchMatrix(int[][] matrix, int target) {
# 5. 有序矩阵的 Kth Element
[378. Kth Smallest Element in a Sorted Matrix ((Medium))](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/description/)
378\. Kth Smallest Element in a Sorted Matrix ((Medium))
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/description/) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-sorted-matrix/description/)
```html
matrix = [
@ -128,7 +138,9 @@ k = 8,
return 13.
```
解题参考：[Share my thoughts and Clean Java Code](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173)
<EFBFBD><EFBFBD>题参考：[Share my thoughts and Clean Java Code
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173)
二分查找解法：
@ -181,7 +193,9 @@ class Tuple implements Comparable<Tuple> {
# 6. 一个数组元素在 [1, n] 之间，其中一个数被替换为另一个数，找出重复的数和丢失的数
[645. Set Mismatch (Easy)](https://leetcode.com/problems/set-mismatch/description/)
645\. Set Mismatch (Easy)
[Leetcode](https://leetcode.com/problems/set-mismatch/description/) / [力扣](https://leetcode-cn.com/problems/set-mismatch/description/)
```html
Input: nums = [1,2,2,4]
@ -221,12 +235,18 @@ private void swap(int[] nums, int i, int j) {
类似题目：
- [448. Find All Numbers Disappeared in an Array (Easy)](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元素
- [442. Find All Duplicates in an Array (Medium)](https://leetcode.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素。
[448\. Find All Numbers Disappeared in an Array (Easy)
[Leetcode](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元<EFBFBD>)
[442\. Find All Duplicates in an Array (Medium)
[Leetcode](https://leetcode.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素<EFBFBD>)
# 7. 找出数组中重复的数，数组值在 [1, n] 之间
[287. Find the Duplicate Number (Medium)](https://leetcode.com/problems/find-the-duplicate-number/description/)
287\. Find the Duplicate Number (Medium)
[Leetcode](https://leetcode.com/problems/find-the-duplicate-number/description/) / [力扣](https://leetcode-cn.com/problems/find-the-duplicate-number/description/)
要求不能修改数组，也不能使用额外的空间。
@ -268,7 +288,9 @@ public int findDuplicate(int[] nums) {
# 8. 数组相邻差值的个数
[667. Beautiful Arrangement II (Medium)](https://leetcode.com/problems/beautiful-arrangement-ii/description/)
667\. Beautiful Arrangement II (Medium)
[Leetcode](https://leetcode.com/problems/beautiful-arrangement-ii/description/) / [力扣](https://leetcode-cn.com/problems/beautiful-arrangement-ii/description/)
```html
Input: n = 3, k = 2
@ -296,7 +318,9 @@ public int[] constructArray(int n, int k) {
# 9. 数组的度
[697. Degree of an Array (Easy)](https://leetcode.com/problems/degree-of-an-array/description/)
697\. Degree of an Array (Easy)
[Leetcode](https://leetcode.com/problems/degree-of-an-array/description/) / [力扣](https://leetcode-cn.com/problems/degree-of-an-array/description/)
```html
Input: [1,2,2,3,1,4,2]
@ -335,7 +359,9 @@ public int findShortestSubArray(int[] nums) {
# 10. 对角元素相等的矩阵
[766. Toeplitz Matrix (Easy)](https://leetcode.com/problems/toeplitz-matrix/description/)
766\. Toeplitz Matrix (Easy)
[Leetcode](https://leetcode.com/problems/toeplitz-matrix/description/) / [力扣](https://leetcode-cn.com/problems/toeplitz-matrix/description/)
```html
1234
@ -373,7 +399,9 @@ private boolean check(int[][] matrix, int expectValue, int row, int col) {
# 11. 嵌套数组
[565. Array Nesting (Medium)](https://leetcode.com/problems/array-nesting/description/)
565\. Array Nesting (Medium)
[Leetcode](https://leetcode.com/problems/array-nesting/description/) / [力扣](https://leetcode-cn.com/problems/array-nesting/description/)
```html
Input: A = [5,4,0,3,1,6,2]
@ -407,7 +435,9 @@ public int arrayNesting(int[] nums) {
# 12. 分隔数组
[769. Max Chunks To Make Sorted (Medium)](https://leetcode.com/problems/max-chunks-to-make-sorted/description/)
769\. Max Chunks To Make Sorted (Medium)
[Leetcode](https://leetcode.com/problems/max-chunks-to-make-sorted/description/) / [力扣](https://leetcode-cn.com/problems/max-chunks-to-make-sorted/description/)
```html
Input: arr = [1,0,2,3,4]

24
docs/notes/Leetcode 题解 - 栈和队列.md
View File

@ -10,7 +10,9 @@
# 1. 用栈实现队列
[232. Implement Queue using Stacks (Easy)](https://leetcode.com/problems/implement-queue-using-stacks/description/)
232\. Implement Queue using Stacks (Easy)
[Leetcode](https://leetcode.com/problems/implement-queue-using-stacks/description/) / [力扣](https://leetcode-cn.com/problems/implement-queue-using-stacks/description/)
栈的顺序为后进先出，而队列的顺序为先进先出。使用两个栈实现队列，一个元素需要经过两个栈才能出队列，在经过第一个栈时元素顺序被反转，经过第二个栈时再次被反转，此时就是先进先出顺序。
@ -50,7 +52,9 @@ class MyQueue {
# 2. 用队列实现栈
[225. Implement Stack using Queues (Easy)](https://leetcode.com/problems/implement-stack-using-queues/description/)
225\. Implement Stack using Queues (Easy)
[Leetcode](https://leetcode.com/problems/implement-stack-using-queues/description/) / [力扣](https://leetcode-cn.com/problems/implement-stack-using-queues/description/)
在将一个元素 x 插入队列时，为了维护原来的后进先出顺序，需要让 x 插入队列首部。而队列的默认插入顺序是队列尾部，因此在将 x 插入队列尾部之后，需要让除了 x 之外的所有元素出队列，再入队列。
@ -87,7 +91,9 @@ class MyStack {
# 3. 最小值栈
[155. Min Stack (Easy)](https://leetcode.com/problems/min-stack/description/)
155\. Min Stack (Easy)
[Leetcode](https://leetcode.com/problems/min-stack/description/) / [力扣](https://leetcode-cn.com/problems/min-stack/description/)
```java
class MinStack {
@ -128,7 +134,9 @@ class MinStack {
# 4. 用栈实现括号匹配
[20. Valid Parentheses (Easy)](https://leetcode.com/problems/valid-parentheses/description/)
20\. Valid Parentheses (Easy)
[Leetcode](https://leetcode.com/problems/valid-parentheses/description/) / [力扣](https://leetcode-cn.com/problems/valid-parentheses/description/)
```html
"()[]{}"
@ -161,7 +169,9 @@ public boolean isValid(String s) {
# 5. 数组中元素与下一个比它大的元素之间的距离
[739. Daily Temperatures (Medium)](https://leetcode.com/problems/daily-temperatures/description/)
739\. Daily Temperatures (Medium)
[Leetcode](https://leetcode.com/problems/daily-temperatures/description/) / [力扣](https://leetcode-cn.com/problems/daily-temperatures/description/)
```html
Input: [73, 74, 75, 71, 69, 72, 76, 73]
@ -188,7 +198,9 @@ public int[] dailyTemperatures(int[] temperatures) {
# 6. 循环数组中比当前元素大的下一个元素
[503. Next Greater Element II (Medium)](https://leetcode.com/problems/next-greater-element-ii/description/)
503\. Next Greater Element II (Medium)
[Leetcode](https://leetcode.com/problems/next-greater-element-ii/description/) / [力扣](https://leetcode-cn.com/problems/next-greater-element-ii/description/)
```text
Input: [1,2,1]

124
docs/notes/Leetcode 题解 - 树.md
View File

@ -44,7 +44,9 @@
## 1. 树的高度
[104. Maximum Depth of Binary Tree (Easy)](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/)
104\. Maximum Depth of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/description/)
```java
public int maxDepth(TreeNode root) {
@ -55,7 +57,9 @@ public int maxDepth(TreeNode root) {
## 2. 平衡树
[110. Balanced Binary Tree (Easy)](https://leetcode.com/problems/balanced-binary-tree/description/)
110\. Balanced Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/balanced-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/balanced-binary-tree/description/)
```html
3
@ -86,7 +90,9 @@ public int maxDepth(TreeNode root) {
## 3. 两节点的最长路径
[543. Diameter of Binary Tree (Easy)](https://leetcode.com/problems/diameter-of-binary-tree/description/)
543\. Diameter of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/diameter-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/diameter-of-binary-tree/description/)
```html
Input:
@ -119,7 +125,9 @@ private int depth(TreeNode root) {
## 4. 翻转树
[226. Invert Binary Tree (Easy)](https://leetcode.com/problems/invert-binary-tree/description/)
226\. Invert Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/invert-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/invert-binary-tree/description/)
```java
public TreeNode invertTree(TreeNode root) {
@ -133,7 +141,9 @@ public TreeNode invertTree(TreeNode root) {
## 5. 归并两棵树
[617. Merge Two Binary Trees (Easy)](https://leetcode.com/problems/merge-two-binary-trees/description/)
617\. Merge Two Binary Trees (Easy)
[Leetcode](https://leetcode.com/problems/merge-two-binary-trees/description/) / [力扣](https://leetcode-cn.com/problems/merge-two-binary-trees/description/)
```html
Input:
@ -166,7 +176,9 @@ public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
## 6. 判断路径和是否等于一个数
[Leetcdoe : 112. Path Sum (Easy)](https://leetcode.com/problems/path-sum/description/)
Leetcdoe : 112. Path Sum (Easy)
[Leetcode](https://leetcode.com/problems/path-sum/description/) / [力扣](https://leetcode-cn.com/problems/path-sum/description/)
```html
Given the below binary tree and sum = 22,
@ -194,7 +206,9 @@ public boolean hasPathSum(TreeNode root, int sum) {
## 7. 统计路径和等于一个数的路径数量
[437. Path Sum III (Easy)](https://leetcode.com/problems/path-sum-iii/description/)
437\. Path Sum III (Easy)
[Leetcode](https://leetcode.com/problems/path-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/path-sum-iii/description/)
```html
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
@ -234,7 +248,9 @@ private int pathSumStartWithRoot(TreeNode root, int sum) {
## 8. 子树
[572. Subtree of Another Tree (Easy)](https://leetcode.com/problems/subtree-of-another-tree/description/)
572\. Subtree of Another Tree (Easy)
[Leetcode](https://leetcode.com/problems/subtree-of-another-tree/description/) / [力扣](https://leetcode-cn.com/problems/subtree-of-another-tree/description/)
```html
Given tree s:
@ -285,7 +301,9 @@ private boolean isSubtreeWithRoot(TreeNode s, TreeNode t) {
## 9. 树的对称
[101. Symmetric Tree (Easy)](https://leetcode.com/problems/symmetric-tree/description/)
101\. Symmetric Tree (Easy)
[Leetcode](https://leetcode.com/problems/symmetric-tree/description/) / [力扣](https://leetcode-cn.com/problems/symmetric-tree/description/)
```html
1
@ -311,7 +329,9 @@ private boolean isSymmetric(TreeNode t1, TreeNode t2) {
## 10. 最小路径
[111. Minimum Depth of Binary Tree (Easy)](https://leetcode.com/problems/minimum-depth-of-binary-tree/description/)
111\. Minimum Depth of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/minimum-depth-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/description/)
树的根节点到叶子节点的最小路径长度
@ -327,7 +347,9 @@ public int minDepth(TreeNode root) {
## 11. 统计左叶子节点的和
[404. Sum of Left Leaves (Easy)](https://leetcode.com/problems/sum-of-left-leaves/description/)
404\. Sum of Left Leaves (Easy)
[Leetcode](https://leetcode.com/problems/sum-of-left-leaves/description/) / [力扣](https://leetcode-cn.com/problems/sum-of-left-leaves/description/)
```html
3
@ -354,7 +376,9 @@ private boolean isLeaf(TreeNode node){
## 12. 相同节点值的最大路径长度
[687. Longest Univalue Path (Easy)](https://leetcode.com/problems/longest-univalue-path/)
687\. Longest Univalue Path (Easy)
[Leetcode](https://leetcode.com/problems/longest-univalue-path/) / [力扣](https://leetcode-cn.com/problems/longest-univalue-path/)
```html
1
@ -387,7 +411,9 @@ private int dfs(TreeNode root){
## 13. 间隔遍历
[337. House Robber III (Medium)](https://leetcode.com/problems/house-robber-iii/description/)
337\. House Robber III (Medium)
[Leetcode](https://leetcode.com/problems/house-robber-iii/description/) / [力扣](https://leetcode-cn.com/problems/house-robber-iii/description/)
```html
3
@ -411,7 +437,9 @@ public int rob(TreeNode root) {
## 14. 找出二叉树中第二小的节点
[671. Second Minimum Node In a Binary Tree (Easy)](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/description/)
671\. Second Minimum Node In a Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/second-minimum-node-in-a-binary-tree/description/)
```html
Input:
@ -446,7 +474,9 @@ public int findSecondMinimumValue(TreeNode root) {
## 1. 一棵树每层节点的平均数
[637. Average of Levels in Binary Tree (Easy)](https://leetcode.com/problems/average-of-levels-in-binary-tree/description/)
637\. Average of Levels in Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/average-of-levels-in-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/description/)
```java
public List<Double> averageOfLevels(TreeNode root) {
@ -471,7 +501,9 @@ public List<Double> averageOfLevels(TreeNode root) {
## 2. 得到左下角的节点
[513. Find Bottom Left Tree Value (Easy)](https://leetcode.com/problems/find-bottom-left-tree-value/description/)
513\. Find Bottom Left Tree Value (Easy)
[Leetcode](https://leetcode.com/problems/find-bottom-left-tree-value/description/) / [力扣](https://leetcode-cn.com/problems/find-bottom-left-tree-value/description/)
```html
Input:
@ -552,7 +584,9 @@ void dfs(TreeNode root) {
## 1. 非递归实现二叉树的前序遍历
[144. Binary Tree Preorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-preorder-traversal/description/)
144\. Binary Tree Preorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-preorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-preorder-traversal/description/)
```java
public List<Integer> preorderTraversal(TreeNode root) {
@ -572,7 +606,9 @@ public List<Integer> preorderTraversal(TreeNode root) {
## 2. 非递归实现二叉树的后序遍历
[145. Binary Tree Postorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-postorder-traversal/description/)
145\. Binary Tree Postorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-postorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-postorder-traversal/description/)
前序遍历为 root -> left -> right，后序遍历为 left -> right -> root。可以修改前序遍历成为 root -> right -> left，那么这个顺序就和后序遍历正好相反。
@ -595,7 +631,9 @@ public List<Integer> postorderTraversal(TreeNode root) {
## 3. 非递归实现二叉树的中序遍历
[94. Binary Tree Inorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-inorder-traversal/description/)
94\. Binary Tree Inorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-inorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-inorder-traversal/description/)
```java
public List<Integer> inorderTraversal(TreeNode root) {
@ -624,7 +662,9 @@ public List<Integer> inorderTraversal(TreeNode root) {
## 1. 修剪二叉查找树
[669. Trim a Binary Search Tree (Easy)](https://leetcode.com/problems/trim-a-binary-search-tree/description/)
669\. Trim a Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/trim-a-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/trim-a-binary-search-tree/description/)
```html
Input:
@ -664,7 +704,9 @@ public TreeNode trimBST(TreeNode root, int L, int R) {
## 2. 寻找二叉查找树的第 k 个元素
[230. Kth Smallest Element in a BST (Medium)](https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/)
230\. Kth Smallest Element in a BST (Medium)
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-bst/description/)
中序遍历解法：
@ -708,7 +750,9 @@ private int count(TreeNode node) {
## 3. 把二叉查找树每个节点的值都加上比它大的节点的值
[Convert BST to Greater Tree (Easy)](https://leetcode.com/problems/convert-bst-to-greater-tree/description/)
Convert BST to Greater Tree (Easy)
[Leetcode](https://leetcode.com/problems/convert-bst-to-greater-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-bst-to-greater-tree/description/)
```html
Input: The root of a Binary Search Tree like this:
@ -745,7 +789,9 @@ private void traver(TreeNode node) {
## 4. 二叉查找树的最近公共祖先
[235. Lowest Common Ancestor of a Binary Search Tree (Easy)](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/)
235\. Lowest Common Ancestor of a Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/)
```html
_______6______
@ -769,7 +815,9 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
## 5. 二叉树的最近公共祖先
[236. Lowest Common Ancestor of a Binary Tree (Medium) ](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/)
236\. Lowest Common Ancestor of a Binary Tree (Medium)
[Leetcode](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/description/)
```html
_______3______
@ -794,7 +842,9 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
## 6. 从有序数组中构造二叉查找树
[108. Convert Sorted Array to Binary Search Tree (Easy)](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/)
108\. Convert Sorted Array to Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/description/)
```java
public TreeNode sortedArrayToBST(int[] nums) {
@ -813,7 +863,9 @@ private TreeNode toBST(int[] nums, int sIdx, int eIdx){
## 7. 根据有序链表构造平衡的二叉查找树
[109. Convert Sorted List to Binary Search Tree (Medium)](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/)
109\. Convert Sorted List to Binary Search Tree (Medium)
[Leetcode](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-sorted-list-to-binary-search-tree/description/)
```html
Given the sorted linked list: [-10,-3,0,5,9],
@ -854,7 +906,9 @@ private ListNode preMid(ListNode head) {
## 8. 在二叉查找树中寻找两个节点，使它们的和为一个给定值
[653. Two Sum IV - Input is a BST (Easy)](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/)
653\. Two Sum IV - Input is a BST (Easy)
[Leetcode](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/) / [力扣](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/description/)
```html
Input:
@ -898,7 +952,9 @@ private void inOrder(TreeNode root, List<Integer> nums) {
## 9. 在二叉查找树中查找两个节点之差的最小绝对值
[530. Minimum Absolute Difference in BST (Easy)](https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/)
530\. Minimum Absolute Difference in BST (Easy)
[Leetcode](https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/) / [力扣](https://leetcode-cn.com/problems/minimum-absolute-difference-in-bst/description/)
```html
Input:
@ -936,7 +992,9 @@ private void inOrder(TreeNode node) {
## 10. 寻找二叉查找树中出现次数最多的值
[501. Find Mode in Binary Search Tree (Easy)](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/)
501\. Find Mode in Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/find-mode-in-binary-search-tree/description/)
```html
1
@ -993,7 +1051,9 @@ Trie，又称前缀树或字典树，用于判断字符串是否存在或者是
## 1. 实现一个 Trie
[208. Implement Trie (Prefix Tree) (Medium)](https://leetcode.com/problems/implement-trie-prefix-tree/description/)
208\. Implement Trie (Prefix Tree) (Medium)
[Leetcode](https://leetcode.com/problems/implement-trie-prefix-tree/description/) / [力扣](https://leetcode-cn.com/problems/implement-trie-prefix-tree/description/)
```java
class Trie {
@ -1055,7 +1115,9 @@ class Trie {
## 2. 实现一个 Trie，用来求前缀和
[677. Map Sum Pairs (Medium)](https://leetcode.com/problems/map-sum-pairs/description/)
677\. Map Sum Pairs (Medium)
[Leetcode](https://leetcode.com/problems/map-sum-pairs/description/) / [力扣](https://leetcode-cn.com/problems/map-sum-pairs/description/)
```html
Input: insert("apple", 3), Output: Null

44
docs/notes/Leetcode 题解 - 贪心思想.md
View File

@ -17,7 +17,9 @@
# 1. 分配饼干
[455. Assign Cookies (Easy)](https://leetcode.com/problems/assign-cookies/description/)
455\. Assign Cookies (Easy)
[Leetcode](https://leetcode.com/problems/assign-cookies/description/) / [力扣](https://leetcode-cn.com/problems/assign-cookies/description/)
```html
Input: [1,2], [1,2,3]
@ -51,7 +53,9 @@ public int findContentChildren(int[] g, int[] s) {
# 2. 不重叠的区间个数
[435. Non-overlapping Intervals (Medium)](https://leetcode.com/problems/non-overlapping-intervals/description/)
435\. Non-overlapping Intervals (Medium)
[Leetcode](https://leetcode.com/problems/non-overlapping-intervals/description/) / [力扣](https://leetcode-cn.com/problems/non-overlapping-intervals/description/)
```html
Input: [ [1,2], [1,2], [1,2] ]
@ -109,7 +113,9 @@ Arrays.sort(intervals, new Comparator<int[]>() {
# 3. 投飞镖刺破气球
[452. Minimum Number of Arrows to Burst Balloons (Medium)](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/description/)
452\. Minimum Number of Arrows to Burst Balloons (Medium)
[Leetcode](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/description/) / [力扣](https://leetcode-cn.com/problems/minimum-number-of-arrows-to-burst-balloons/description/)
```
Input:
@ -143,7 +149,9 @@ public int findMinArrowShots(int[][] points) {
# 4. 根据身高和序号重组队列
[406. Queue Reconstruction by Height(Medium)](https://leetcode.com/problems/queue-reconstruction-by-height/description/)
406\. Queue Reconstruction by Height(Medium)
[Leetcode](https://leetcode.com/problems/queue-reconstruction-by-height/description/) / [力扣](https://leetcode-cn.com/problems/queue-reconstruction-by-height/description/)
```html
Input:
@ -175,7 +183,9 @@ public int[][] reconstructQueue(int[][] people) {
# 5. 买卖股票最大的收益
[121. Best Time to Buy and Sell Stock (Easy)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/)
121\. Best Time to Buy and Sell Stock (Easy)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock/description/)
题目描述：一次股票交易包含买入和卖出，只进行一次交易，求最大收益。
@ -198,7 +208,9 @@ public int maxProfit(int[] prices) {
# 6. 买卖股票的最大收益 II
[122. Best Time to Buy and Sell Stock II (Easy)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/)
122\. Best Time to Buy and Sell Stock II (Easy)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-ii/description/)
题目描述：可以进行多次交易，多次交易之间不能交叉进行，可以进行多次交易。
@ -219,7 +231,9 @@ public int maxProfit(int[] prices) {
# 7. 种植花朵
[605. Can Place Flowers (Easy)](https://leetcode.com/problems/can-place-flowers/description/)
605\. Can Place Flowers (Easy)
[Leetcode](https://leetcode.com/problems/can-place-flowers/description/) / [力扣](https://leetcode-cn.com/problems/can-place-flowers/description/)
```html
Input: flowerbed = [1,0,0,0,1], n = 1
@ -249,7 +263,9 @@ public boolean canPlaceFlowers(int[] flowerbed, int n) {
# 8. 判断是否为子序列
[392. Is Subsequence (Medium)](https://leetcode.com/problems/is-subsequence/description/)
392\. Is Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/is-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/is-subsequence/description/)
```html
s = "abc", t = "ahbgdc"
@ -271,7 +287,9 @@ public boolean isSubsequence(String s, String t) {
# 9. 修改一个数成为非递减数组
[665. Non-decreasing Array (Easy)](https://leetcode.com/problems/non-decreasing-array/description/)
665\. Non-decreasing Array (Easy)
[Leetcode](https://leetcode.com/problems/non-decreasing-array/description/) / [力扣](https://leetcode-cn.com/problems/non-decreasing-array/description/)
```html
Input: [4,2,3]
@ -305,7 +323,9 @@ public boolean checkPossibility(int[] nums) {
# 10. 子数组最大的和
[53. Maximum Subarray (Easy)](https://leetcode.com/problems/maximum-subarray/description/)
53\. Maximum Subarray (Easy)
[Leetcode](https://leetcode.com/problems/maximum-subarray/description/) / [力扣](https://leetcode-cn.com/problems/maximum-subarray/description/)
```html
For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
@ -329,7 +349,9 @@ public int maxSubArray(int[] nums) {
# 11. 分隔字符串使同种字符出现在一起
[763. Partition Labels (Medium)](https://leetcode.com/problems/partition-labels/description/)
763\. Partition Labels (Medium)
[Leetcode](https://leetcode.com/problems/partition-labels/description/) / [力扣](https://leetcode-cn.com/problems/partition-labels/description/)
```html
Input: S = "ababcbacadefegdehijhklij"

40
docs/notes/Leetcode 题解 - 链表.md
View File

@ -16,7 +16,9 @@
# 1. 找出两个链表的交点
[160. Intersection of Two Linked Lists (Easy)](https://leetcode.com/problems/intersection-of-two-linked-lists/description/)
160\. Intersection of Two Linked Lists (Easy)
[Leetcode](https://leetcode.com/problems/intersection-of-two-linked-lists/description/) / [力扣](https://leetcode-cn.com/problems/intersection-of-two-linked-lists/description/)
例如以下示例中 A 和 B 两个链表相交于 c1：
@ -66,7 +68,9 @@ public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
# 2. 链表反转
[206. Reverse Linked List (Easy)](https://leetcode.com/problems/reverse-linked-list/description/)
206\. Reverse Linked List (Easy)
[Leetcode](https://leetcode.com/problems/reverse-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/reverse-linked-list/description/)
递归
@ -100,7 +104,9 @@ public ListNode reverseList(ListNode head) {
# 3. 归并两个有序的链表
[21. Merge Two Sorted Lists (Easy)](https://leetcode.com/problems/merge-two-sorted-lists/description/)
21\. Merge Two Sorted Lists (Easy)
[Leetcode](https://leetcode.com/problems/merge-two-sorted-lists/description/) / [力扣](https://leetcode-cn.com/problems/merge-two-sorted-lists/description/)
```java
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
@ -118,7 +124,9 @@ public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
# 4. 从有序链表中删除重复节点
[83. Remove Duplicates from Sorted List (Easy)](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/)
83\. Remove Duplicates from Sorted List (Easy)
[Leetcode](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/) / [力扣](https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list/description/)
```html
Given 1->1->2, return 1->2.
@ -135,7 +143,9 @@ public ListNode deleteDuplicates(ListNode head) {
# 5. 删除链表的倒数第 n 个节点
[19. Remove Nth Node From End of List (Medium)](https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/)
19\. Remove Nth Node From End of List (Medium)
[Leetcode](https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/) / [力扣](https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/description/)
```html
Given linked list: 1->2->3->4->5, and n = 2.
@ -161,7 +171,9 @@ public ListNode removeNthFromEnd(ListNode head, int n) {
# 6. 交换链表中的相邻结点
[24. Swap Nodes in Pairs (Medium)](https://leetcode.com/problems/swap-nodes-in-pairs/description/)
24\. Swap Nodes in Pairs (Medium)
[Leetcode](https://leetcode.com/problems/swap-nodes-in-pairs/description/) / [力扣](https://leetcode-cn.com/problems/swap-nodes-in-pairs/description/)
```html
Given 1->2->3->4, you should return the list as 2->1->4->3.
@ -189,7 +201,9 @@ public ListNode swapPairs(ListNode head) {
# 7. 链表求和
[445. Add Two Numbers II (Medium)](https://leetcode.com/problems/add-two-numbers-ii/description/)
445\. Add Two Numbers II (Medium)
[Leetcode](https://leetcode.com/problems/add-two-numbers-ii/description/) / [力扣](https://leetcode-cn.com/problems/add-two-numbers-ii/description/)
```html
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
@ -228,7 +242,9 @@ private Stack<Integer> buildStack(ListNode l) {
# 8. 回文链表
[234. Palindrome Linked List (Easy)](https://leetcode.com/problems/palindrome-linked-list/description/)
234\. Palindrome Linked List (Easy)
[Leetcode](https://leetcode.com/problems/palindrome-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-linked-list/description/)
题目要求：以 O(1) 的空间复杂度来求解。
@ -277,7 +293,9 @@ private boolean isEqual(ListNode l1, ListNode l2) {
# 9. 分隔链表
[725. Split Linked List in Parts(Medium)](https://leetcode.com/problems/split-linked-list-in-parts/description/)
725\. Split Linked List in Parts(Medium)
[Leetcode](https://leetcode.com/problems/split-linked-list-in-parts/description/) / [力扣](https://leetcode-cn.com/problems/split-linked-list-in-parts/description/)
```html
Input:
@ -317,7 +335,9 @@ public ListNode[] splitListToParts(ListNode root, int k) {
# 10. 链表元素按奇偶聚集
[328. Odd Even Linked List (Medium)](https://leetcode.com/problems/odd-even-linked-list/description/)
328\. Odd Even Linked List (Medium)
[Leetcode](https://leetcode.com/problems/odd-even-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/odd-even-linked-list/description/)
```html
Example:

24
notes/Leetcode 题解 - 二分查找.md
View File

@ -96,7 +96,9 @@ l m h
# 1. 求开方
[69. Sqrt(x) (Easy)](https://leetcode.com/problems/sqrtx/description/)
69\. Sqrt(x) (Easy)
[Leetcode](https://leetcode.com/problems/sqrtx/description/) / [力扣](https://leetcode-cn.com/problems/sqrtx/description/)
```html
Input: 4
@ -134,7 +136,9 @@ public int mySqrt(int x) {
# 2. 大于给定元素的最小元素
[744. Find Smallest Letter Greater Than Target (Easy)](https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/)
744\. Find Smallest Letter Greater Than Target (Easy)
[Leetcode](https://leetcode.com/problems/find-smallest-letter-greater-than-target/description/) / [力扣](https://leetcode-cn.com/problems/find-smallest-letter-greater-than-target/description/)
```html
Input:
@ -168,7 +172,9 @@ public char nextGreatestLetter(char[] letters, char target) {
# 3. 有序数组的 Single Element
[540. Single Element in a Sorted Array (Medium)](https://leetcode.com/problems/single-element-in-a-sorted-array/description/)
540\. Single Element in a Sorted Array (Medium)
[Leetcode](https://leetcode.com/problems/single-element-in-a-sorted-array/description/) / [力扣](https://leetcode-cn.com/problems/single-element-in-a-sorted-array/description/)
```html
Input: [1, 1, 2, 3, 3, 4, 4, 8, 8]
@ -205,7 +211,9 @@ public int singleNonDuplicate(int[] nums) {
# 4. 第一个错误的版本
[278. First Bad Version (Easy)](https://leetcode.com/problems/first-bad-version/description/)
278\. First Bad Version (Easy)
[Leetcode](https://leetcode.com/problems/first-bad-version/description/) / [力扣](https://leetcode-cn.com/problems/first-bad-version/description/)
题目描述：给定一个元素 n 代表有 [1, 2, ..., n] 版本，在第 x 位置开始出现错误版本，导致后面的版本都错误。可以调用 isBadVersion(int x) 知道某个版本是否错误，要求找到第一个错误的版本。
@ -230,7 +238,9 @@ public int firstBadVersion(int n) {
# 5. 旋转数组的最小数字
[153. Find Minimum in Rotated Sorted Array (Medium)](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/)
153\. Find Minimum in Rotated Sorted Array (Medium)
[Leetcode](https://leetcode.com/problems/find-minimum-in-rotated-sorted-array/description/) / [力扣](https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array/description/)
```html
Input: [3,4,5,1,2],
@ -254,7 +264,9 @@ public int findMin(int[] nums) {
# 6. 查找区间
[34. Find First and Last Position of Element in Sorted Array](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/)
34\. Find First and Last Position of Element in Sorted Array
[Leetcode](https://leetcode.com/problems/find-first-and-last-position-of-element-in-sorted-array/) / [力扣](https://leetcode-cn.com/problems/find-first-and-last-position-of-element-in-sorted-array/)
```html
Input: nums = [5,7,7,8,8,10], target = 8

48
notes/Leetcode 题解 - 位运算.md
View File

@ -61,7 +61,9 @@ static String toBinaryString(int i); // 转换为二进制表示的字符串
# 1. 统计两个数的二进制表示有多少位不同
[461. Hamming Distance (Easy)](https://leetcode.com/problems/hamming-distance/)
461. Hamming Distance (Easy)
[Leetcode](https://leetcode.com/problems/hamming-distance/) / [力扣](https://leetcode-cn.com/problems/hamming-distance/)
```html
Input: x = 1, y = 4
@ -114,7 +116,9 @@ public int hammingDistance(int x, int y) {
# 2. 数组中唯一一个不重复的元素
[136. Single Number (Easy)](https://leetcode.com/problems/single-number/description/)
136\. Single Number (Easy)
[Leetcode](https://leetcode.com/problems/single-number/description/) / [力扣](https://leetcode-cn.com/problems/single-number/description/)
```html
Input: [4,1,2,1,2]
@ -133,7 +137,9 @@ public int singleNumber(int[] nums) {
# 3. 找出数组中缺失的那个数
[268. Missing Number (Easy)](https://leetcode.com/problems/missing-number/description/)
268\. Missing Number (Easy)
[Leetcode](https://leetcode.com/problems/missing-number/description/) / [力扣](https://leetcode-cn.com/problems/missing-number/description/)
```html
Input: [3,0,1]
@ -154,7 +160,9 @@ public int missingNumber(int[] nums) {
# 4. 数组中不重复的两个元素
[260. Single Number III (Medium)](https://leetcode.com/problems/single-number-iii/description/)
260\. Single Number III (Medium)
[Leetcode](https://leetcode.com/problems/single-number-iii/description/) / [力扣](https://leetcode-cn.com/problems/single-number-iii/description/)
两个不相等的元素在位级表示上必定会有一位存在不同。
@ -178,7 +186,9 @@ public int[] singleNumber(int[] nums) {
# 5. 翻转一个数的比特位
[190. Reverse Bits (Easy)](https://leetcode.com/problems/reverse-bits/description/)
190\. Reverse Bits (Easy)
[Leetcode](https://leetcode.com/problems/reverse-bits/description/) / [力扣](https://leetcode-cn.com/problems/reverse-bits/description/)
```java
public int reverseBits(int n) {
@ -233,7 +243,9 @@ a = a ^ b;
# 7. 判断一个数是不是 2 的 n 次方
[231. Power of Two (Easy)](https://leetcode.com/problems/power-of-two/description/)
231\. Power of Two (Easy)
[Leetcode](https://leetcode.com/problems/power-of-two/description/) / [力扣](https://leetcode-cn.com/problems/power-of-two/description/)
二进制表示只有一个 1 存在。
@ -253,7 +265,9 @@ public boolean isPowerOfTwo(int n) {
# 8. 判断一个数是不是 4 的 n 次方
[342. Power of Four (Easy)](https://leetcode.com/problems/power-of-four/)
342\. Power of Four (Easy)
[Leetcode](https://leetcode.com/problems/power-of-four/) / [力扣](https://leetcode-cn.com/problems/power-of-four/)
这种数在二进制表示中有且只有一个奇数位为 1，例如 16（10000）。
@ -273,7 +287,9 @@ public boolean isPowerOfFour(int num) {
# 9. 判断一个数的位级表示是否不会出现连续的 0 和 1
[693. Binary Number with Alternating Bits (Easy)](https://leetcode.com/problems/binary-number-with-alternating-bits/description/)
693\. Binary Number with Alternating Bits (Easy)
[Leetcode](https://leetcode.com/problems/binary-number-with-alternating-bits/description/) / [力扣](https://leetcode-cn.com/problems/binary-number-with-alternating-bits/description/)
```html
Input: 10
@ -298,7 +314,9 @@ public boolean hasAlternatingBits(int n) {
# 10. 求一个数的补码
[476. Number Complement (Easy)](https://leetcode.com/problems/number-complement/description/)
476\. Number Complement (Easy)
[Leetcode](https://leetcode.com/problems/number-complement/description/) / [力扣](https://leetcode-cn.com/problems/number-complement/description/)
```html
Input: 5
@ -353,7 +371,9 @@ public int findComplement(int num) {
# 11. 实现整数的加法
[371. Sum of Two Integers (Easy)](https://leetcode.com/problems/sum-of-two-integers/description/)
371\. Sum of Two Integers (Easy)
[Leetcode](https://leetcode.com/problems/sum-of-two-integers/description/) / [力扣](https://leetcode-cn.com/problems/sum-of-two-integers/description/)
a ^ b 表示没有考虑进位的情况下两数的和，(a & b) << 1 就是进位。
@ -367,7 +387,9 @@ public int getSum(int a, int b) {
# 12. 字符串数组最大乘积
[318. Maximum Product of Word Lengths (Medium)](https://leetcode.com/problems/maximum-product-of-word-lengths/description/)
318\. Maximum Product of Word Lengths (Medium)
[Leetcode](https://leetcode.com/problems/maximum-product-of-word-lengths/description/) / [力扣](https://leetcode-cn.com/problems/maximum-product-of-word-lengths/description/)
```html
Given ["abcw", "baz", "foo", "bar", "xtfn", "abcdef"]
@ -402,7 +424,9 @@ public int maxProduct(String[] words) {
# 13. 统计从 0 \~ n 每个数的二进制表示中 1 的个数
[338. Counting Bits (Medium)](https://leetcode.com/problems/counting-bits/description/)
338\. Counting Bits (Medium)
[Leetcode](https://leetcode.com/problems/counting-bits/description/) / [力扣](https://leetcode-cn.com/problems/counting-bits/description/)
对于数字 6(110)，它可以看成是 4(100) 再加一个 2(10)，因此 dp[i] = dp[i&(i-1)] + 1;

8
notes/Leetcode 题解 - 分治.md
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@ -6,7 +6,9 @@
# 1. 给表达式加括号
[241. Different Ways to Add Parentheses (Medium)](https://leetcode.com/problems/different-ways-to-add-parentheses/description/)
241\. Different Ways to Add Parentheses (Medium)
[Leetcode](https://leetcode.com/problems/different-ways-to-add-parentheses/description/) / [力扣](https://leetcode-cn.com/problems/different-ways-to-add-parentheses/description/)
```html
Input: "2-1-1".
@ -51,7 +53,9 @@ public List<Integer> diffWaysToCompute(String input) {
# 2. 不同的二叉搜索树
[95. Unique Binary Search Trees II (Medium)](https://leetcode.com/problems/unique-binary-search-trees-ii/description/)
95\. Unique Binary Search Trees II (Medium)
[Leetcode](https://leetcode.com/problems/unique-binary-search-trees-ii/description/) / [力扣](https://leetcode-cn.com/problems/unique-binary-search-trees-ii/description/)
给定一个数字 n，要求生成所有值为 1...n 的二叉搜索树。

108
notes/Leetcode 题解 - 动态规划.md
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@ -46,7 +46,9 @@
## 1. 爬楼梯
[70. Climbing Stairs (Easy)](https://leetcode.com/problems/climbing-stairs/description/)
70\. Climbing Stairs (Easy)
[Leetcode](https://leetcode.com/problems/climbing-stairs/description/) / [力扣](https://leetcode-cn.com/problems/climbing-stairs/description/)
题目描述：有 N 阶楼梯，每次可以上一阶或者两阶，求有多少种上楼梯的方法。
@ -77,7 +79,9 @@ public int climbStairs(int n) {
## 2. 强盗抢劫
[198. House Robber (Easy)](https://leetcode.com/problems/house-robber/description/)
198\. House Robber (Easy)
[Leetcode](https://leetcode.com/problems/house-robber/description/) / [力扣](https://leetcode-cn.com/problems/house-robber/description/)
题目描述：抢劫一排住户，但是不能抢邻近的住户，求最大抢劫量。
@ -103,7 +107,9 @@ public int rob(int[] nums) {
## 3. 强盗在环形街区抢劫
[213. House Robber II (Medium)](https://leetcode.com/problems/house-robber-ii/description/)
213\. House Robber II (Medium)
[Leetcode](https://leetcode.com/problems/house-robber-ii/description/) / [力扣](https://leetcode-cn.com/problems/house-robber-ii/description/)
```java
public int rob(int[] nums) {
@ -159,7 +165,9 @@ private int rob(int[] nums, int first, int last) {
## 1. 矩阵的最小路径和
[64. Minimum Path Sum (Medium)](https://leetcode.com/problems/minimum-path-sum/description/)
64\. Minimum Path Sum (Medium)
[Leetcode](https://leetcode.com/problems/minimum-path-sum/description/) / [力扣](https://leetcode-cn.com/problems/minimum-path-sum/description/)
```html
[[1,3,1],
@ -195,7 +203,9 @@ public int minPathSum(int[][] grid) {
## 2. 矩阵的总路径数
[62. Unique Paths (Medium)](https://leetcode.com/problems/unique-paths/description/)
62\. Unique Paths (Medium)
[Leetcode](https://leetcode.com/problems/unique-paths/description/) / [力扣](https://leetcode-cn.com/problems/unique-paths/description/)
题目描述：统计从矩阵左上角到右下角的路径总数，每次只能向右或者向下移动。
@ -232,7 +242,9 @@ public int uniquePaths(int m, int n) {
## 1. 数组区间和
[303. Range Sum Query - Immutable (Easy)](https://leetcode.com/problems/range-sum-query-immutable/description/)
303\. Range Sum Query - Immutable (Easy)
[Leetcode](https://leetcode.com/problems/range-sum-query-immutable/description/) / [力扣](https://leetcode-cn.com/problems/range-sum-query-immutable/description/)
```html
Given nums = [-2, 0, 3, -5, 2, -1]
@ -264,7 +276,9 @@ class NumArray {
## 2. 数组中等差递增子区间的个数
[413. Arithmetic Slices (Medium)](https://leetcode.com/problems/arithmetic-slices/description/)
413\. Arithmetic Slices (Medium)
[Leetcode](https://leetcode.com/problems/arithmetic-slices/description/) / [力扣](https://leetcode-cn.com/problems/arithmetic-slices/description/)
```html
A = [0, 1, 2, 3, 4]
@ -323,7 +337,9 @@ public int numberOfArithmeticSlices(int[] A) {
## 1. 分割整数的最大乘积
[343. Integer Break (Medim)](https://leetcode.com/problems/integer-break/description/)
343\. Integer Break (Medim)
[Leetcode](https://leetcode.com/problems/integer-break/description/) / [力扣](https://leetcode-cn.com/problems/integer-break/description/)
题目描述：For example, given n = 2, return 1 (2 = 1 + 1); given n = 10, return 36 (10 = 3 + 3 + 4).
@ -342,7 +358,9 @@ public int integerBreak(int n) {
## 2. 按平方数来分割整数
[279. Perfect Squares(Medium)](https://leetcode.com/problems/perfect-squares/description/)
279\. Perfect Squares(Medium)
[Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/)
题目描述：For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.
@ -378,7 +396,9 @@ private List<Integer> generateSquareList(int n) {
## 3. 分割整数构成字母字符串
[91. Decode Ways (Medium)](https://leetcode.com/problems/decode-ways/description/)
91\. Decode Ways (Medium)
[Leetcode](https://leetcode.com/problems/decode-ways/description/) / [力扣](https://leetcode-cn.com/problems/decode-ways/description/)
题目描述：Given encoded message "12", it could be decoded as "AB" (1 2) or "L" (12).
@ -426,7 +446,9 @@ public int numDecodings(String s) {
## 1. 最长递增子序列
[300. Longest Increasing Subsequence (Medium)](https://leetcode.com/problems/longest-increasing-subsequence/description/)
300\. Longest Increasing Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/longest-increasing-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-increasing-subsequence/description/)
```java
public int lengthOfLIS(int[] nums) {
@ -508,7 +530,9 @@ private int binarySearch(int[] tails, int len, int key) {
## 2. 一组整数对能够构成的最长链
[646. Maximum Length of Pair Chain (Medium)](https://leetcode.com/problems/maximum-length-of-pair-chain/description/)
646\. Maximum Length of Pair Chain (Medium)
[Leetcode](https://leetcode.com/problems/maximum-length-of-pair-chain/description/) / [力扣](https://leetcode-cn.com/problems/maximum-length-of-pair-chain/description/)
```html
Input: [[1,2], [2,3], [3,4]]
@ -540,7 +564,9 @@ public int findLongestChain(int[][] pairs) {
## 3. 最长摆动子序列
[376. Wiggle Subsequence (Medium)](https://leetcode.com/problems/wiggle-subsequence/description/)
376\. Wiggle Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/wiggle-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/wiggle-subsequence/description/)
```html
Input: [1,7,4,9,2,5]
@ -697,7 +723,9 @@ public int knapsack(int W, int N, int[] weights, int[] values) {
## 1. 划分数组为和相等的两部分
[416. Partition Equal Subset Sum (Medium)](https://leetcode.com/problems/partition-equal-subset-sum/description/)
416\. Partition Equal Subset Sum (Medium)
[Leetcode](https://leetcode.com/problems/partition-equal-subset-sum/description/) / [力扣](https://leetcode-cn.com/problems/partition-equal-subset-sum/description/)
```html
Input: [1, 5, 11, 5]
@ -737,7 +765,9 @@ private int computeArraySum(int[] nums) {
## 2. 改变一组数的正负号使得它们的和为一给定数
[494. Target Sum (Medium)](https://leetcode.com/problems/target-sum/description/)
494\. Target Sum (Medium)
[Leetcode](https://leetcode.com/problems/target-sum/description/) / [力扣](https://leetcode-cn.com/problems/target-sum/description/)
```html
Input: nums is [1, 1, 1, 1, 1], S is 3.
@ -809,7 +839,9 @@ private int findTargetSumWays(int[] nums, int start, int S) {
## 3. 01 字符构成最多的字符串
[474. Ones and Zeroes (Medium)](https://leetcode.com/problems/ones-and-zeroes/description/)
474\. Ones and Zeroes (Medium)
[Leetcode](https://leetcode.com/problems/ones-and-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/ones-and-zeroes/description/)
```html
Input: Array = {"10", "0001", "111001", "1", "0"}, m = 5, n = 3
@ -847,7 +879,9 @@ public int findMaxForm(String[] strs, int m, int n) {
## 4. 找零钱的最少硬币数
[322. Coin Change (Medium)](https://leetcode.com/problems/coin-change/description/)
322\. Coin Change (Medium)
[Leetcode](https://leetcode.com/problems/coin-change/description/) / [力扣](https://leetcode-cn.com/problems/coin-change/description/)
```html
Example 1:
@ -888,7 +922,9 @@ public int coinChange(int[] coins, int amount) {
## 5. 找零钱的硬币数组合
[518\. Coin Change 2 (Medium)](https://leetcode.com/problems/coin-change-2/description/)
518\. Coin Change 2 (Medium)
[Leetcode](https://leetcode.com/problems/coin-change-2/description/) / [力扣](https://leetcode-cn.com/problems/coin-change-2/description/)
```text-html-basic
Input: amount = 5, coins = [1, 2, 5]
@ -920,7 +956,9 @@ public int change(int amount, int[] coins) {
## 6. 字符串按单词列表分割
[139. Word Break (Medium)](https://leetcode.com/problems/word-break/description/)
139\. Word Break (Medium)
[Leetcode](https://leetcode.com/problems/word-break/description/) / [力扣](https://leetcode-cn.com/problems/word-break/description/)
```html
s = "leetcode",
@ -957,7 +995,9 @@ public boolean wordBreak(String s, List<String> wordDict) {
## 7. 组合总和
[377. Combination Sum IV (Medium)](https://leetcode.com/problems/combination-sum-iv/description/)
377\. Combination Sum IV (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-iv/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iv/description/)
```html
nums = [1, 2, 3]
@ -1000,7 +1040,9 @@ public int combinationSum4(int[] nums, int target) {
## 1. 需要冷却期的股票交易
[309. Best Time to Buy and Sell Stock with Cooldown(Medium)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/)
309\. Best Time to Buy and Sell Stock with Cooldown(Medium)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-cooldown/description/)
题目描述：交易之后需要有一天的冷却时间。
@ -1030,7 +1072,9 @@ public int maxProfit(int[] prices) {
## 2. 需要交易费用的股票交易
[714. Best Time to Buy and Sell Stock with Transaction Fee (Medium)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/)
714\. Best Time to Buy and Sell Stock with Transaction Fee (Medium)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-with-transaction-fee/description/)
```html
Input: prices = [1, 3, 2, 8, 4, 9], fee = 2
@ -1069,7 +1113,9 @@ public int maxProfit(int[] prices, int fee) {
## 3. 只能进行两次的股票交易
[123. Best Time to Buy and Sell Stock III (Hard)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/description/)
123\. Best Time to Buy and Sell Stock III (Hard)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iii/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iii/description/)
```java
public int maxProfit(int[] prices) {
@ -1095,7 +1141,9 @@ public int maxProfit(int[] prices) {
## 4. 只能进行 k 次的股票交易
[188. Best Time to Buy and Sell Stock IV (Hard)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/description/)
188\. Best Time to Buy and Sell Stock IV (Hard)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-iv/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-iv/description/)
```java
public int maxProfit(int k, int[] prices) {
@ -1125,7 +1173,9 @@ public int maxProfit(int k, int[] prices) {
## 1. 删除两个字符串的字符使它们相等
[583. Delete Operation for Two Strings (Medium)](https://leetcode.com/problems/delete-operation-for-two-strings/description/)
583\. Delete Operation for Two Strings (Medium)
[Leetcode](https://leetcode.com/problems/delete-operation-for-two-strings/description/) / [力扣](https://leetcode-cn.com/problems/delete-operation-for-two-strings/description/)
```html
Input: "sea", "eat"
@ -1154,7 +1204,9 @@ public int minDistance(String word1, String word2) {
## 2. 编辑距离
[72. Edit Distance (Hard)](https://leetcode.com/problems/edit-distance/description/)
72\. Edit Distance (Hard)
[Leetcode](https://leetcode.com/problems/edit-distance/description/) / [力扣](https://leetcode-cn.com/problems/edit-distance/description/)
```html
Example 1:
@ -1207,7 +1259,9 @@ public int minDistance(String word1, String word2) {
## 3. 复制粘贴字符
[650. 2 Keys Keyboard (Medium)](https://leetcode.com/problems/2-keys-keyboard/description/)
650\. 2 Keys Keyboard (Medium)
[Leetcode](https://leetcode.com/problems/2-keys-keyboard/description/) / [力扣](https://leetcode-cn.com/problems/2-keys-keyboard/description/)
题目描述：最开始只有一个字符 A，问需要多少次操作能够得到 n 个字符 A，每次操作可以复制当前所有的字符，或者粘贴。

20
notes/Leetcode 题解 - 哈希表.md
View File

@ -10,12 +10,16 @@
- Java 中的 **HashSet** 用于存储一个集合，可以查找元素是否在集合中。如果元素有穷，并且范围不大，那么可以用一个布尔数组来存储一个元素是否存在。例如对于只有小写字符的元素，就可以用一个长度为 26 的布尔数组来存储一个字符集合，使得空间复杂度降低为 O(1)。
- Java 中的 **HashMap** 主要用于映射关系，从而把两个元素联系起来。HashMap 也可以用来对元素进行计数统计，此时键为元素，值为计数。和 HashSet 类似，如果元素有穷并且范围不大，可以用整型数组来进行统计。在对一个内容进行压缩或者其它转换时，利用 HashMap 可以把原始内容和转换后的内容联系起来。例如在一个简化 url 的系统中 [Leetcdoe : 535. Encode and Decode TinyURL (Medium)](https://leetcode.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源。
Java 中的 **HashMap** 主要用于映射关系，从而把两个元素联系起来。HashMap 也可以用来对元素进行计数统计，此时键为元素，值为计数。和 HashSet 类似，如果元素有穷并且范围不大，可以用整型数组来进行统计。在对一个内容进行压缩或者其它转换时，利用 HashMap 可以把原始内容和转换后的内容联系起来。例如在一个简化 url 的系统中 [Leetcdoe : 535. Encode and Decode TinyURL (Medium)
[Leetcode](https://leetcode.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/encode-and-decode-tinyurl/description/)，利用 HashMap 就可以存储精简后的 url 到原始 url 的映射，使得不仅可以显示简化的 url，也可以根据简化的 url 得到原始 url 从而定位到正确的资源<EFBFBD>)
# 1. 数组中两个数的和为给定值
[1. Two Sum (Easy)](https://leetcode.com/problems/two-sum/description/)
1\. Two Sum (Easy)
[Leetcode](https://leetcode.com/problems/two-sum/description/) / [力扣](https://leetcode-cn.com/problems/two-sum/description/)
可以先对数组进行排序，然后使用双指针方法或者二分查找方法。这样做的时间复杂度为 O(NlogN)，空间复杂度为 O(1)。
@ -37,7 +41,9 @@ public int[] twoSum(int[] nums, int target) {
# 2. 判断数组是否含有重复元素
[217. Contains Duplicate (Easy)](https://leetcode.com/problems/contains-duplicate/description/)
217\. Contains Duplicate (Easy)
[Leetcode](https://leetcode.com/problems/contains-duplicate/description/) / [力扣](https://leetcode-cn.com/problems/contains-duplicate/description/)
```java
public boolean containsDuplicate(int[] nums) {
@ -51,7 +57,9 @@ public boolean containsDuplicate(int[] nums) {
# 3. 最长和谐序列
[594. Longest Harmonious Subsequence (Easy)](https://leetcode.com/problems/longest-harmonious-subsequence/description/)
594\. Longest Harmonious Subsequence (Easy)
[Leetcode](https://leetcode.com/problems/longest-harmonious-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-harmonious-subsequence/description/)
```html
Input: [1,3,2,2,5,2,3,7]
@ -79,7 +87,9 @@ public int findLHS(int[] nums) {
# 4. 最长连续序列
[128. Longest Consecutive Sequence (Hard)](https://leetcode.com/problems/longest-consecutive-sequence/description/)
128\. Longest Consecutive Sequence (Hard)
[Leetcode](https://leetcode.com/problems/longest-consecutive-sequence/description/) / [力扣](https://leetcode-cn.com/problems/longest-consecutive-sequence/description/)
```html
Given [100, 4, 200, 1, 3, 2],

16
notes/Leetcode 题解 - 图.md
View File

@ -15,7 +15,9 @@
## 1. 判断是否为二分图
[785. Is Graph Bipartite? (Medium)](https://leetcode.com/problems/is-graph-bipartite/description/)
785\. Is Graph Bipartite? (Medium)
[Leetcode](https://leetcode.com/problems/is-graph-bipartite/description/) / [力扣](https://leetcode-cn.com/problems/is-graph-bipartite/description/)
```html
Input: [[1,3], [0,2], [1,3], [0,2]]
@ -74,7 +76,9 @@ private boolean isBipartite(int curNode, int curColor, int[] colors, int[][] gra
## 1. 课程安排的合法性
[207. Course Schedule (Medium)](https://leetcode.com/problems/course-schedule/description/)
207\. Course Schedule (Medium)
[Leetcode](https://leetcode.com/problems/course-schedule/description/) / [力扣](https://leetcode-cn.com/problems/course-schedule/description/)
```html
2, [[1,0]]
@ -132,7 +136,9 @@ private boolean hasCycle(boolean[] globalMarked, boolean[] localMarked,
## 2. 课程安排的顺序
[210. Course Schedule II (Medium)](https://leetcode.com/problems/course-schedule-ii/description/)
210\. Course Schedule II (Medium)
[Leetcode](https://leetcode.com/problems/course-schedule-ii/description/) / [力扣](https://leetcode-cn.com/problems/course-schedule-ii/description/)
```html
4, [[1,0],[2,0],[3,1],[3,2]]
@ -195,7 +201,9 @@ private boolean hasCycle(boolean[] globalMarked, boolean[] localMarked, List<Int
## 1. 冗余连接
[684. Redundant Connection (Medium)](https://leetcode.com/problems/redundant-connection/description/)
684\. Redundant Connection (Medium)
[Leetcode](https://leetcode.com/problems/redundant-connection/description/) / [力扣](https://leetcode-cn.com/problems/redundant-connection/description/)
```html
Input: [[1,2], [1,3], [2,3]]

24
notes/Leetcode 题解 - 字符串.md
View File

@ -50,7 +50,9 @@ Return "student a am I"
# 4. 两个字符串包含的字符是否完全相同
[242. Valid Anagram (Easy)](https://leetcode.com/problems/valid-anagram/description/)
242\. Valid Anagram (Easy)
[Leetcode](https://leetcode.com/problems/valid-anagram/description/) / [力扣](https://leetcode-cn.com/problems/valid-anagram/description/)
```html
s = "anagram", t = "nagaram", return true.
@ -81,7 +83,9 @@ public boolean isAnagram(String s, String t) {
# 5. 计算一组字符集合可以组成的回文字符串的最大长度
[409. Longest Palindrome (Easy)](https://leetcode.com/problems/longest-palindrome/description/)
409\. Longest Palindrome (Easy)
[Leetcode](https://leetcode.com/problems/longest-palindrome/description/) / [力扣](https://leetcode-cn.com/problems/longest-palindrome/description/)
```html
Input : "abccccdd"
@ -112,7 +116,9 @@ public int longestPalindrome(String s) {
# 6. 字符串同构
[205. Isomorphic Strings (Easy)](https://leetcode.com/problems/isomorphic-strings/description/)
205\. Isomorphic Strings (Easy)
[Leetcode](https://leetcode.com/problems/isomorphic-strings/description/) / [力扣](https://leetcode-cn.com/problems/isomorphic-strings/description/)
```html
Given "egg", "add", return true.
@ -140,7 +146,9 @@ public boolean isIsomorphic(String s, String t) {
# 7. 回文子字符串个数
[647. Palindromic Substrings (Medium)](https://leetcode.com/problems/palindromic-substrings/description/)
647\. Palindromic Substrings (Medium)
[Leetcode](https://leetcode.com/problems/palindromic-substrings/description/) / [力扣](https://leetcode-cn.com/problems/palindromic-substrings/description/)
```html
Input: "aaa"
@ -172,7 +180,9 @@ private void extendSubstrings(String s, int start, int end) {
# 8. 判断一个整数是否是回文数
[9. Palindrome Number (Easy)](https://leetcode.com/problems/palindrome-number/description/)
9\. Palindrome Number (Easy)
[Leetcode](https://leetcode.com/problems/palindrome-number/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-number/description/)
要求不能使用额外空间，也就不能将整数转换为字符串进行判断。
@ -197,7 +207,9 @@ public boolean isPalindrome(int x) {
# 9. 统计二进制字符串中连续 1 和连续 0 数量相同的子字符串个数
[696. Count Binary Substrings (Easy)](https://leetcode.com/problems/count-binary-substrings/description/)
696\. Count Binary Substrings (Easy)
[Leetcode](https://leetcode.com/problems/count-binary-substrings/description/) / [力扣](https://leetcode-cn.com/problems/count-binary-substrings/description/)
```html
Input: "00110011"

16
notes/Leetcode 题解 - 排序.md
View File

@ -28,7 +28,9 @@
## 1. Kth Element
[215. Kth Largest Element in an Array (Medium)](https://leetcode.com/problems/kth-largest-element-in-an-array/description/)
215\. Kth Largest Element in an Array (Medium)
[Leetcode](https://leetcode.com/problems/kth-largest-element-in-an-array/description/) / [力扣](https://leetcode-cn.com/problems/kth-largest-element-in-an-array/description/)
```text
Input: [3,2,1,5,6,4] and k = 2
@ -104,7 +106,9 @@ private void swap(int[] a, int i, int j) {
## 1. 出现频率最多的 k 个元素
[347. Top K Frequent Elements (Medium)](https://leetcode.com/problems/top-k-frequent-elements/description/)
347\. Top K Frequent Elements (Medium)
[Leetcode](https://leetcode.com/problems/top-k-frequent-elements/description/) / [力扣](https://leetcode-cn.com/problems/top-k-frequent-elements/description/)
```html
Given [1,1,1,2,2,3] and k = 2, return [1,2].
@ -145,7 +149,9 @@ public List<Integer> topKFrequent(int[] nums, int k) {
## 2. 按照字符出现次数对字符串排序
[451. Sort Characters By Frequency (Medium)](https://leetcode.com/problems/sort-characters-by-frequency/description/)
451\. Sort Characters By Frequency (Medium)
[Leetcode](https://leetcode.com/problems/sort-characters-by-frequency/description/) / [力扣](https://leetcode-cn.com/problems/sort-characters-by-frequency/description/)
```html
Input:
@ -199,7 +205,9 @@ public String frequencySort(String s) {
## 1. 按颜色进行排序
[75. Sort Colors (Medium)](https://leetcode.com/problems/sort-colors/description/)
75\. Sort Colors (Medium)
[Leetcode](https://leetcode.com/problems/sort-colors/description/) / [力扣](https://leetcode-cn.com/problems/sort-colors/description/)
```html
Input: [2,0,2,1,1,0]

92
notes/Leetcode 题解 - 搜索.md
View File

@ -61,7 +61,9 @@
## 1. 计算在网格中从原点到特定点的最短路径长度
[1091. Shortest Path in Binary Matrix(Medium)](https://leetcode.com/problems/shortest-path-in-binary-matrix/)
1091\. Shortest Path in Binary Matrix(Medium)
[Leetcode](https://leetcode.com/problems/shortest-path-in-binary-matrix/) / [力扣](https://leetcode-cn.com/problems/shortest-path-in-binary-matrix/)
```html
[[1,1,0,1],
@ -104,7 +106,9 @@ public int shortestPathBinaryMatrix(int[][] grids) {
## 2. 组成整数的最小平方数数量
[279. Perfect Squares (Medium)](https://leetcode.com/problems/perfect-squares/description/)
279\. Perfect Squares (Medium)
[Leetcode](https://leetcode.com/problems/perfect-squares/description/) / [力扣](https://leetcode-cn.com/problems/perfect-squares/description/)
```html
For example, given n = 12, return 3 because 12 = 4 + 4 + 4; given n = 13, return 2 because 13 = 4 + 9.
@ -167,7 +171,9 @@ private List<Integer> generateSquares(int n) {
## 3. 最短单词路径
[127. Word Ladder (Medium)](https://leetcode.com/problems/word-ladder/description/)
127\. Word Ladder (Medium)
[Leetcode](https://leetcode.com/problems/word-ladder/description/) / [力扣](https://leetcode-cn.com/problems/word-ladder/description/)
```html
Input:
@ -278,7 +284,9 @@ private int getShortestPath(List<Integer>[] graphic, int start, int end) {
## 1. 查找最大的连通面积
[695. Max Area of Island (Medium)](https://leetcode.com/problems/max-area-of-island/description/)
695\. Max Area of Island (Medium)
[Leetcode](https://leetcode.com/problems/max-area-of-island/description/) / [力扣](https://leetcode-cn.com/problems/max-area-of-island/description/)
```html
[[0,0,1,0,0,0,0,1,0,0,0,0,0],
@ -325,7 +333,9 @@ private int dfs(int[][] grid, int r, int c) {
## 2. 矩阵中的连通分量数目
[200. Number of Islands (Medium)](https://leetcode.com/problems/number-of-islands/description/)
200\. Number of Islands (Medium)
[Leetcode](https://leetcode.com/problems/number-of-islands/description/) / [力扣](https://leetcode-cn.com/problems/number-of-islands/description/)
```html
Input:
@ -374,7 +384,9 @@ private void dfs(char[][] grid, int i, int j) {
## 3. 好友关系的连通分量数目
[547. Friend Circles (Medium)](https://leetcode.com/problems/friend-circles/description/)
547\. Friend Circles (Medium)
[Leetcode](https://leetcode.com/problems/friend-circles/description/) / [力扣](https://leetcode-cn.com/problems/friend-circles/description/)
```html
Input:
@ -418,7 +430,9 @@ private void dfs(int[][] M, int i, boolean[] hasVisited) {
## 4. 填充封闭区域
[130. Surrounded Regions (Medium)](https://leetcode.com/problems/surrounded-regions/description/)
130\. Surrounded Regions (Medium)
[Leetcode](https://leetcode.com/problems/surrounded-regions/description/) / [力扣](https://leetcode-cn.com/problems/surrounded-regions/description/)
```html
For example,
@ -483,7 +497,9 @@ private void dfs(char[][] board, int r, int c) {
## 5. 能到达的太平洋和大西洋的区域
[417. Pacific Atlantic Water Flow (Medium)](https://leetcode.com/problems/pacific-atlantic-water-flow/description/)
417\. Pacific Atlantic Water Flow (Medium)
[Leetcode](https://leetcode.com/problems/pacific-atlantic-water-flow/description/) / [力扣](https://leetcode-cn.com/problems/pacific-atlantic-water-flow/description/)
```html
Given the following 5x5 matrix:
@ -571,7 +587,9 @@ Backtracking（回溯）属于 DFS。
## 1. 数字键盘组合
[17. Letter Combinations of a Phone Number (Medium)](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/)
17\. Letter Combinations of a Phone Number (Medium)
[Leetcode](https://leetcode.com/problems/letter-combinations-of-a-phone-number/description/) / [力扣](https://leetcode-cn.com/problems/letter-combinations-of-a-phone-number/description/)
<div align="center"> <img src="pics/9823768c-212b-4b1a-b69a-b3f59e07b977.jpg"/> </div><br>
@ -609,7 +627,9 @@ private void doCombination(StringBuilder prefix, List<String> combinations, fina
## 2. IP 地址划分
[93. Restore IP Addresses(Medium)](https://leetcode.com/problems/restore-ip-addresses/description/)
93\. Restore IP Addresses(Medium)
[Leetcode](https://leetcode.com/problems/restore-ip-addresses/description/) / [力扣](https://leetcode-cn.com/problems/restore-ip-addresses/description/)
```html
Given "25525511135",
@ -650,7 +670,9 @@ private void doRestore(int k, StringBuilder tempAddress, List<String> addresses,
## 3. 在矩阵中寻找字符串
[79. Word Search (Medium)](https://leetcode.com/problems/word-search/description/)
79\. Word Search (Medium)
[Leetcode](https://leetcode.com/problems/word-search/description/) / [力扣](https://leetcode-cn.com/problems/word-search/description/)
```html
For example,
@ -719,7 +741,9 @@ private boolean backtracking(int curLen, int r, int c, boolean[][] visited, fina
## 4. 输出二叉树中所有从根到叶子的路径
[257. Binary Tree Paths (Easy)](https://leetcode.com/problems/binary-tree-paths/description/)
257\. Binary Tree Paths (Easy)
[Leetcode](https://leetcode.com/problems/binary-tree-paths/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-paths/description/)
```html
1
@ -777,7 +801,9 @@ private String buildPath(List<Integer> values) {
## 5. 排列
[46. Permutations (Medium)](https://leetcode.com/problems/permutations/description/)
46\. Permutations (Medium)
[Leetcode](https://leetcode.com/problems/permutations/description/) / [力扣](https://leetcode-cn.com/problems/permutations/description/)
```html
[1,2,3] have the following permutations:
@ -820,7 +846,9 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
## 6. 含有相同元素求排列
[47. Permutations II (Medium)](https://leetcode.com/problems/permutations-ii/description/)
47\. Permutations II (Medium)
[Leetcode](https://leetcode.com/problems/permutations-ii/description/) / [力扣](https://leetcode-cn.com/problems/permutations-ii/description/)
```html
[1,1,2] have the following unique permutations:
@ -865,7 +893,9 @@ private void backtracking(List<Integer> permuteList, List<List<Integer>> permute
## 7. 组合
[77. Combinations (Medium)](https://leetcode.com/problems/combinations/description/)
77\. Combinations (Medium)
[Leetcode](https://leetcode.com/problems/combinations/description/) / [力扣](https://leetcode-cn.com/problems/combinations/description/)
```html
If n = 4 and k = 2, a solution is:
@ -902,7 +932,9 @@ private void backtracking(List<Integer> combineList, List<List<Integer>> combina
## 8. 组合求和
[39. Combination Sum (Medium)](https://leetcode.com/problems/combination-sum/description/)
39\. Combination Sum (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum/description/)
```html
given candidate set [2, 3, 6, 7] and target 7,
@ -936,7 +968,9 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
## 9. 含有相同元素的组合求和
[40. Combination Sum II (Medium)](https://leetcode.com/problems/combination-sum-ii/description/)
40\. Combination Sum II (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-ii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-ii/description/)
```html
For example, given candidate set [10, 1, 2, 7, 6, 1, 5] and target 8,
@ -981,7 +1015,9 @@ private void backtracking(List<Integer> tempCombination, List<List<Integer>> com
## 10. 1-9 数字的组合求和
[216. Combination Sum III (Medium)](https://leetcode.com/problems/combination-sum-iii/description/)
216\. Combination Sum III (Medium)
[Leetcode](https://leetcode.com/problems/combination-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/combination-sum-iii/description/)
```html
Input: k = 3, n = 9
@ -1021,7 +1057,9 @@ private void backtracking(int k, int n, int start,
## 11. 子集
[78. Subsets (Medium)](https://leetcode.com/problems/subsets/description/)
78\. Subsets (Medium)
[Leetcode](https://leetcode.com/problems/subsets/description/) / [力扣](https://leetcode-cn.com/problems/subsets/description/)
找出集合的所有子集，子集不能重复，[1, 2] 和 [2, 1] 这种子集算重复
@ -1052,7 +1090,9 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
## 12. 含有相同元素求子集
[90. Subsets II (Medium)](https://leetcode.com/problems/subsets-ii/description/)
90\. Subsets II (Medium)
[Leetcode](https://leetcode.com/problems/subsets-ii/description/) / [力扣](https://leetcode-cn.com/problems/subsets-ii/description/)
```html
For example,
@ -1102,7 +1142,9 @@ private void backtracking(int start, List<Integer> tempSubset, List<List<Integer
## 13. 分割字符串使得每个部分都是回文数
[131. Palindrome Partitioning (Medium)](https://leetcode.com/problems/palindrome-partitioning/description/)
131\. Palindrome Partitioning (Medium)
[Leetcode](https://leetcode.com/problems/palindrome-partitioning/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-partitioning/description/)
```html
For example, given s = "aab",
@ -1148,7 +1190,9 @@ private boolean isPalindrome(String s, int begin, int end) {
## 14. 数独
[37. Sudoku Solver (Hard)](https://leetcode.com/problems/sudoku-solver/description/)
37\. Sudoku Solver (Hard)
[Leetcode](https://leetcode.com/problems/sudoku-solver/description/) / [力扣](https://leetcode-cn.com/problems/sudoku-solver/description/)
<div align="center"> <img src="pics/0e8fdc96-83c1-4798-9abe-45fc91d70b9d.png"/> </div><br>
@ -1205,7 +1249,9 @@ private int cubeNum(int i, int j) {
## 15. N 皇后
[51. N-Queens (Hard)](https://leetcode.com/problems/n-queens/description/)
51\. N-Queens (Hard)
[Leetcode](https://leetcode.com/problems/n-queens/description/) / [力扣](https://leetcode-cn.com/problems/n-queens/description/)
<div align="center"> <img src="pics/067b310c-6877-40fe-9dcf-10654e737485.jpg"/> </div><br>

52
notes/Leetcode 题解 - 数学.md
View File

@ -46,7 +46,9 @@ x 和 y 的最小公倍数为：lcm(x,y) = 2<sup>max(m0,n0)</sup> \* 3<sup>max(
## 1. 生成素数序列
[204. Count Primes (Easy)](https://leetcode.com/problems/count-primes/description/)
204\. Count Primes (Easy)
[Leetcode](https://leetcode.com/problems/count-primes/description/) / [力扣](https://leetcode-cn.com/problems/count-primes/description/)
埃拉托斯特尼筛法在每次找到一个素数时，将能被素数整除的数排除掉。
@ -122,7 +124,9 @@ public int gcd(int a, int b) {
## 1. 7 进制
[504. Base 7 (Easy)](https://leetcode.com/problems/base-7/description/)
504\. Base 7 (Easy)
[Leetcode](https://leetcode.com/problems/base-7/description/) / [力扣](https://leetcode-cn.com/problems/base-7/description/)
```java
public String convertToBase7(int num) {
@ -153,7 +157,9 @@ public String convertToBase7(int num) {
## 2. 16 进制
[405. Convert a Number to Hexadecimal (Easy)](https://leetcode.com/problems/convert-a-number-to-hexadecimal/description/)
405\. Convert a Number to Hexadecimal (Easy)
[Leetcode](https://leetcode.com/problems/convert-a-number-to-hexadecimal/description/) / [力扣](https://leetcode-cn.com/problems/convert-a-number-to-hexadecimal/description/)
```html
Input:
@ -186,7 +192,9 @@ public String toHex(int num) {
## 3. 26 进制
[168. Excel Sheet Column Title (Easy)](https://leetcode.com/problems/excel-sheet-column-title/description/)
168\. Excel Sheet Column Title (Easy)
[Leetcode](https://leetcode.com/problems/excel-sheet-column-title/description/) / [力扣](https://leetcode-cn.com/problems/excel-sheet-column-title/description/)
```html
1 -> A
@ -214,7 +222,9 @@ public String convertToTitle(int n) {
## 1. 统计阶乘尾部有多少个 0
[172. Factorial Trailing Zeroes (Easy)](https://leetcode.com/problems/factorial-trailing-zeroes/description/)
172\. Factorial Trailing Zeroes (Easy)
[Leetcode](https://leetcode.com/problems/factorial-trailing-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/factorial-trailing-zeroes/description/)
尾部的 0 由 2 * 5 得来，2 的数量明显多于 5 的数量，因此只要统计有多少个 5 即可。
@ -232,7 +242,9 @@ public int trailingZeroes(int n) {
## 1. 二进制加法
[67. Add Binary (Easy)](https://leetcode.com/problems/add-binary/description/)
67\. Add Binary (Easy)
[Leetcode](https://leetcode.com/problems/add-binary/description/) / [力扣](https://leetcode-cn.com/problems/add-binary/description/)
```html
a = "11"
@ -260,7 +272,9 @@ public String addBinary(String a, String b) {
## 2. 字符串加法
[415. Add Strings (Easy)](https://leetcode.com/problems/add-strings/description/)
415\. Add Strings (Easy)
[Leetcode](https://leetcode.com/problems/add-strings/description/) / [力扣](https://leetcode-cn.com/problems/add-strings/description/)
字符串的值为非负整数。
@ -282,7 +296,9 @@ public String addStrings(String num1, String num2) {
## 1. 改变数组元素使所有的数组元素都相等
[462. Minimum Moves to Equal Array Elements II (Medium)](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/description/)
462\. Minimum Moves to Equal Array Elements II (Medium)
[Leetcode](https://leetcode.com/problems/minimum-moves-to-equal-array-elements-ii/description/) / [力扣](https://leetcode-cn.com/problems/minimum-moves-to-equal-array-elements-ii/description/)
```html
Input:
@ -378,7 +394,9 @@ private void swap(int[] nums, int i, int j) {
## 1. 数组中出现次数多于 n / 2 的元素
[169. Majority Element (Easy)](https://leetcode.com/problems/majority-element/description/)
169\. Majority Element (Easy)
[Leetcode](https://leetcode.com/problems/majority-element/description/) / [力扣](https://leetcode-cn.com/problems/majority-element/description/)
先对数组排序，最中间那个数出现次数一定多于 n / 2。
@ -406,7 +424,9 @@ public int majorityElement(int[] nums) {
## 1. 平方数
[367. Valid Perfect Square (Easy)](https://leetcode.com/problems/valid-perfect-square/description/)
367\. Valid Perfect Square (Easy)
[Leetcode](https://leetcode.com/problems/valid-perfect-square/description/) / [力扣](https://leetcode-cn.com/problems/valid-perfect-square/description/)
```html
Input: 16
@ -432,7 +452,9 @@ public boolean isPerfectSquare(int num) {
## 2. 3 的 n 次方
[326. Power of Three (Easy)](https://leetcode.com/problems/power-of-three/description/)
326\. Power of Three (Easy)
[Leetcode](https://leetcode.com/problems/power-of-three/description/) / [力扣](https://leetcode-cn.com/problems/power-of-three/description/)
```java
public boolean isPowerOfThree(int n) {
@ -442,7 +464,9 @@ public boolean isPowerOfThree(int n) {
## 3. 乘积数组
[238. Product of Array Except Self (Medium)](https://leetcode.com/problems/product-of-array-except-self/description/)
238\. Product of Array Except Self (Medium)
[Leetcode](https://leetcode.com/problems/product-of-array-except-self/description/) / [力扣](https://leetcode-cn.com/problems/product-of-array-except-self/description/)
```html
For example, given [1,2,3,4], return [24,12,8,6].
@ -473,7 +497,9 @@ public int[] productExceptSelf(int[] nums) {
## 4. 找出数组中的乘积最大的三个数
[628. Maximum Product of Three Numbers (Easy)](https://leetcode.com/problems/maximum-product-of-three-numbers/description/)
628\. Maximum Product of Three Numbers (Easy)
[Leetcode](https://leetcode.com/problems/maximum-product-of-three-numbers/description/) / [力扣](https://leetcode-cn.com/problems/maximum-product-of-three-numbers/description/)
```html
Input: [1,2,3,4]

60
notes/Leetcode 题解 - 数组与矩阵.md
View File

@ -16,7 +16,9 @@
# 1. 把数组中的 0 移到末尾
[283. Move Zeroes (Easy)](https://leetcode.com/problems/move-zeroes/description/)
283\. Move Zeroes (Easy)
[Leetcode](https://leetcode.com/problems/move-zeroes/description/) / [力扣](https://leetcode-cn.com/problems/move-zeroes/description/)
```html
For example, given nums = [0, 1, 0, 3, 12], after calling your function, nums should be [1, 3, 12, 0, 0].
@ -38,7 +40,9 @@ public void moveZeroes(int[] nums) {
# 2. 改变矩阵维度
[566. Reshape the Matrix (Easy)](https://leetcode.com/problems/reshape-the-matrix/description/)
566\. Reshape the Matrix (Easy)
[Leetcode](https://leetcode.com/problems/reshape-the-matrix/description/) / [力扣](https://leetcode-cn.com/problems/reshape-the-matrix/description/)
```html
Input:
@ -74,7 +78,9 @@ public int[][] matrixReshape(int[][] nums, int r, int c) {
# 3. 找出数组中最长的连续 1
[485. Max Consecutive Ones (Easy)](https://leetcode.com/problems/max-consecutive-ones/description/)
485\. Max Consecutive Ones (Easy)
[Leetcode](https://leetcode.com/problems/max-consecutive-ones/description/) / [力扣](https://leetcode-cn.com/problems/max-consecutive-ones/description/)
```java
public int findMaxConsecutiveOnes(int[] nums) {
@ -89,7 +95,9 @@ public int findMaxConsecutiveOnes(int[] nums) {
# 4. 有序矩阵查找
[240. Search a 2D Matrix II (Medium)](https://leetcode.com/problems/search-a-2d-matrix-ii/description/)
240\. Search a 2D Matrix II (Medium)
[Leetcode](https://leetcode.com/problems/search-a-2d-matrix-ii/description/) / [力扣](https://leetcode-cn.com/problems/search-a-2d-matrix-ii/description/)
```html
[
@ -115,7 +123,9 @@ public boolean searchMatrix(int[][] matrix, int target) {
# 5. 有序矩阵的 Kth Element
[378. Kth Smallest Element in a Sorted Matrix ((Medium))](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/description/)
378\. Kth Smallest Element in a Sorted Matrix ((Medium))
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/description/) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-sorted-matrix/description/)
```html
matrix = [
@ -128,7 +138,9 @@ k = 8,
return 13.
```
解题参考：[Share my thoughts and Clean Java Code](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173)
<EFBFBD><EFBFBD>题参考：[Share my thoughts and Clean Java Code
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-sorted-matrix/discuss/85173)
二分查找解法：
@ -181,7 +193,9 @@ class Tuple implements Comparable<Tuple> {
# 6. 一个数组元素在 [1, n] 之间，其中一个数被替换为另一个数，找出重复的数和丢失的数
[645. Set Mismatch (Easy)](https://leetcode.com/problems/set-mismatch/description/)
645\. Set Mismatch (Easy)
[Leetcode](https://leetcode.com/problems/set-mismatch/description/) / [力扣](https://leetcode-cn.com/problems/set-mismatch/description/)
```html
Input: nums = [1,2,2,4]
@ -221,12 +235,18 @@ private void swap(int[] nums, int i, int j) {
类似题目：
- [448. Find All Numbers Disappeared in an Array (Easy)](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元素
- [442. Find All Duplicates in an Array (Medium)](https://leetcode.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素。
[448\. Find All Numbers Disappeared in an Array (Easy)
[Leetcode](https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/find-all-numbers-disappeared-in-an-array/description/)，寻找所有丢失的元<EFBFBD>)
[442\. Find All Duplicates in an Array (Medium)
[Leetcode](https://leetcode.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素<EFBFBD>) / [力扣](https://leetcode-cn.com/problems/find-all-duplicates-in-an-array/description/)，寻找所有重复的元素<EFBFBD>)
# 7. 找出数组中重复的数，数组值在 [1, n] 之间
[287. Find the Duplicate Number (Medium)](https://leetcode.com/problems/find-the-duplicate-number/description/)
287\. Find the Duplicate Number (Medium)
[Leetcode](https://leetcode.com/problems/find-the-duplicate-number/description/) / [力扣](https://leetcode-cn.com/problems/find-the-duplicate-number/description/)
要求不能修改数组，也不能使用额外的空间。
@ -268,7 +288,9 @@ public int findDuplicate(int[] nums) {
# 8. 数组相邻差值的个数
[667. Beautiful Arrangement II (Medium)](https://leetcode.com/problems/beautiful-arrangement-ii/description/)
667\. Beautiful Arrangement II (Medium)
[Leetcode](https://leetcode.com/problems/beautiful-arrangement-ii/description/) / [力扣](https://leetcode-cn.com/problems/beautiful-arrangement-ii/description/)
```html
Input: n = 3, k = 2
@ -296,7 +318,9 @@ public int[] constructArray(int n, int k) {
# 9. 数组的度
[697. Degree of an Array (Easy)](https://leetcode.com/problems/degree-of-an-array/description/)
697\. Degree of an Array (Easy)
[Leetcode](https://leetcode.com/problems/degree-of-an-array/description/) / [力扣](https://leetcode-cn.com/problems/degree-of-an-array/description/)
```html
Input: [1,2,2,3,1,4,2]
@ -335,7 +359,9 @@ public int findShortestSubArray(int[] nums) {
# 10. 对角元素相等的矩阵
[766. Toeplitz Matrix (Easy)](https://leetcode.com/problems/toeplitz-matrix/description/)
766\. Toeplitz Matrix (Easy)
[Leetcode](https://leetcode.com/problems/toeplitz-matrix/description/) / [力扣](https://leetcode-cn.com/problems/toeplitz-matrix/description/)
```html
1234
@ -373,7 +399,9 @@ private boolean check(int[][] matrix, int expectValue, int row, int col) {
# 11. 嵌套数组
[565. Array Nesting (Medium)](https://leetcode.com/problems/array-nesting/description/)
565\. Array Nesting (Medium)
[Leetcode](https://leetcode.com/problems/array-nesting/description/) / [力扣](https://leetcode-cn.com/problems/array-nesting/description/)
```html
Input: A = [5,4,0,3,1,6,2]
@ -407,7 +435,9 @@ public int arrayNesting(int[] nums) {
# 12. 分隔数组
[769. Max Chunks To Make Sorted (Medium)](https://leetcode.com/problems/max-chunks-to-make-sorted/description/)
769\. Max Chunks To Make Sorted (Medium)
[Leetcode](https://leetcode.com/problems/max-chunks-to-make-sorted/description/) / [力扣](https://leetcode-cn.com/problems/max-chunks-to-make-sorted/description/)
```html
Input: arr = [1,0,2,3,4]

24
notes/Leetcode 题解 - 栈和队列.md
View File

@ -10,7 +10,9 @@
# 1. 用栈实现队列
[232. Implement Queue using Stacks (Easy)](https://leetcode.com/problems/implement-queue-using-stacks/description/)
232\. Implement Queue using Stacks (Easy)
[Leetcode](https://leetcode.com/problems/implement-queue-using-stacks/description/) / [力扣](https://leetcode-cn.com/problems/implement-queue-using-stacks/description/)
栈的顺序为后进先出，而队列的顺序为先进先出。使用两个栈实现队列，一个元素需要经过两个栈才能出队列，在经过第一个栈时元素顺序被反转，经过第二个栈时再次被反转，此时就是先进先出顺序。
@ -50,7 +52,9 @@ class MyQueue {
# 2. 用队列实现栈
[225. Implement Stack using Queues (Easy)](https://leetcode.com/problems/implement-stack-using-queues/description/)
225\. Implement Stack using Queues (Easy)
[Leetcode](https://leetcode.com/problems/implement-stack-using-queues/description/) / [力扣](https://leetcode-cn.com/problems/implement-stack-using-queues/description/)
在将一个元素 x 插入队列时，为了维护原来的后进先出顺序，需要让 x 插入队列首部。而队列的默认插入顺序是队列尾部，因此在将 x 插入队列尾部之后，需要让除了 x 之外的所有元素出队列，再入队列。
@ -87,7 +91,9 @@ class MyStack {
# 3. 最小值栈
[155. Min Stack (Easy)](https://leetcode.com/problems/min-stack/description/)
155\. Min Stack (Easy)
[Leetcode](https://leetcode.com/problems/min-stack/description/) / [力扣](https://leetcode-cn.com/problems/min-stack/description/)
```java
class MinStack {
@ -128,7 +134,9 @@ class MinStack {
# 4. 用栈实现括号匹配
[20. Valid Parentheses (Easy)](https://leetcode.com/problems/valid-parentheses/description/)
20\. Valid Parentheses (Easy)
[Leetcode](https://leetcode.com/problems/valid-parentheses/description/) / [力扣](https://leetcode-cn.com/problems/valid-parentheses/description/)
```html
"()[]{}"
@ -161,7 +169,9 @@ public boolean isValid(String s) {
# 5. 数组中元素与下一个比它大的元素之间的距离
[739. Daily Temperatures (Medium)](https://leetcode.com/problems/daily-temperatures/description/)
739\. Daily Temperatures (Medium)
[Leetcode](https://leetcode.com/problems/daily-temperatures/description/) / [力扣](https://leetcode-cn.com/problems/daily-temperatures/description/)
```html
Input: [73, 74, 75, 71, 69, 72, 76, 73]
@ -188,7 +198,9 @@ public int[] dailyTemperatures(int[] temperatures) {
# 6. 循环数组中比当前元素大的下一个元素
[503. Next Greater Element II (Medium)](https://leetcode.com/problems/next-greater-element-ii/description/)
503\. Next Greater Element II (Medium)
[Leetcode](https://leetcode.com/problems/next-greater-element-ii/description/) / [力扣](https://leetcode-cn.com/problems/next-greater-element-ii/description/)
```text
Input: [1,2,1]

124
notes/Leetcode 题解 - 树.md
View File

@ -44,7 +44,9 @@
## 1. 树的高度
[104. Maximum Depth of Binary Tree (Easy)](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/)
104\. Maximum Depth of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/maximum-depth-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/description/)
```java
public int maxDepth(TreeNode root) {
@ -55,7 +57,9 @@ public int maxDepth(TreeNode root) {
## 2. 平衡树
[110. Balanced Binary Tree (Easy)](https://leetcode.com/problems/balanced-binary-tree/description/)
110\. Balanced Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/balanced-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/balanced-binary-tree/description/)
```html
3
@ -86,7 +90,9 @@ public int maxDepth(TreeNode root) {
## 3. 两节点的最长路径
[543. Diameter of Binary Tree (Easy)](https://leetcode.com/problems/diameter-of-binary-tree/description/)
543\. Diameter of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/diameter-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/diameter-of-binary-tree/description/)
```html
Input:
@ -119,7 +125,9 @@ private int depth(TreeNode root) {
## 4. 翻转树
[226. Invert Binary Tree (Easy)](https://leetcode.com/problems/invert-binary-tree/description/)
226\. Invert Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/invert-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/invert-binary-tree/description/)
```java
public TreeNode invertTree(TreeNode root) {
@ -133,7 +141,9 @@ public TreeNode invertTree(TreeNode root) {
## 5. 归并两棵树
[617. Merge Two Binary Trees (Easy)](https://leetcode.com/problems/merge-two-binary-trees/description/)
617\. Merge Two Binary Trees (Easy)
[Leetcode](https://leetcode.com/problems/merge-two-binary-trees/description/) / [力扣](https://leetcode-cn.com/problems/merge-two-binary-trees/description/)
```html
Input:
@ -166,7 +176,9 @@ public TreeNode mergeTrees(TreeNode t1, TreeNode t2) {
## 6. 判断路径和是否等于一个数
[Leetcdoe : 112. Path Sum (Easy)](https://leetcode.com/problems/path-sum/description/)
Leetcdoe : 112. Path Sum (Easy)
[Leetcode](https://leetcode.com/problems/path-sum/description/) / [力扣](https://leetcode-cn.com/problems/path-sum/description/)
```html
Given the below binary tree and sum = 22,
@ -194,7 +206,9 @@ public boolean hasPathSum(TreeNode root, int sum) {
## 7. 统计路径和等于一个数的路径数量
[437. Path Sum III (Easy)](https://leetcode.com/problems/path-sum-iii/description/)
437\. Path Sum III (Easy)
[Leetcode](https://leetcode.com/problems/path-sum-iii/description/) / [力扣](https://leetcode-cn.com/problems/path-sum-iii/description/)
```html
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
@ -234,7 +248,9 @@ private int pathSumStartWithRoot(TreeNode root, int sum) {
## 8. 子树
[572. Subtree of Another Tree (Easy)](https://leetcode.com/problems/subtree-of-another-tree/description/)
572\. Subtree of Another Tree (Easy)
[Leetcode](https://leetcode.com/problems/subtree-of-another-tree/description/) / [力扣](https://leetcode-cn.com/problems/subtree-of-another-tree/description/)
```html
Given tree s:
@ -285,7 +301,9 @@ private boolean isSubtreeWithRoot(TreeNode s, TreeNode t) {
## 9. 树的对称
[101. Symmetric Tree (Easy)](https://leetcode.com/problems/symmetric-tree/description/)
101\. Symmetric Tree (Easy)
[Leetcode](https://leetcode.com/problems/symmetric-tree/description/) / [力扣](https://leetcode-cn.com/problems/symmetric-tree/description/)
```html
1
@ -311,7 +329,9 @@ private boolean isSymmetric(TreeNode t1, TreeNode t2) {
## 10. 最小路径
[111. Minimum Depth of Binary Tree (Easy)](https://leetcode.com/problems/minimum-depth-of-binary-tree/description/)
111\. Minimum Depth of Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/minimum-depth-of-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/minimum-depth-of-binary-tree/description/)
树的根节点到叶子节点的最小路径长度
@ -327,7 +347,9 @@ public int minDepth(TreeNode root) {
## 11. 统计左叶子节点的和
[404. Sum of Left Leaves (Easy)](https://leetcode.com/problems/sum-of-left-leaves/description/)
404\. Sum of Left Leaves (Easy)
[Leetcode](https://leetcode.com/problems/sum-of-left-leaves/description/) / [力扣](https://leetcode-cn.com/problems/sum-of-left-leaves/description/)
```html
3
@ -354,7 +376,9 @@ private boolean isLeaf(TreeNode node){
## 12. 相同节点值的最大路径长度
[687. Longest Univalue Path (Easy)](https://leetcode.com/problems/longest-univalue-path/)
687\. Longest Univalue Path (Easy)
[Leetcode](https://leetcode.com/problems/longest-univalue-path/) / [力扣](https://leetcode-cn.com/problems/longest-univalue-path/)
```html
1
@ -387,7 +411,9 @@ private int dfs(TreeNode root){
## 13. 间隔遍历
[337. House Robber III (Medium)](https://leetcode.com/problems/house-robber-iii/description/)
337\. House Robber III (Medium)
[Leetcode](https://leetcode.com/problems/house-robber-iii/description/) / [力扣](https://leetcode-cn.com/problems/house-robber-iii/description/)
```html
3
@ -411,7 +437,9 @@ public int rob(TreeNode root) {
## 14. 找出二叉树中第二小的节点
[671. Second Minimum Node In a Binary Tree (Easy)](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/description/)
671\. Second Minimum Node In a Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/second-minimum-node-in-a-binary-tree/description/)
```html
Input:
@ -446,7 +474,9 @@ public int findSecondMinimumValue(TreeNode root) {
## 1. 一棵树每层节点的平均数
[637. Average of Levels in Binary Tree (Easy)](https://leetcode.com/problems/average-of-levels-in-binary-tree/description/)
637\. Average of Levels in Binary Tree (Easy)
[Leetcode](https://leetcode.com/problems/average-of-levels-in-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/average-of-levels-in-binary-tree/description/)
```java
public List<Double> averageOfLevels(TreeNode root) {
@ -471,7 +501,9 @@ public List<Double> averageOfLevels(TreeNode root) {
## 2. 得到左下角的节点
[513. Find Bottom Left Tree Value (Easy)](https://leetcode.com/problems/find-bottom-left-tree-value/description/)
513\. Find Bottom Left Tree Value (Easy)
[Leetcode](https://leetcode.com/problems/find-bottom-left-tree-value/description/) / [力扣](https://leetcode-cn.com/problems/find-bottom-left-tree-value/description/)
```html
Input:
@ -552,7 +584,9 @@ void dfs(TreeNode root) {
## 1. 非递归实现二叉树的前序遍历
[144. Binary Tree Preorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-preorder-traversal/description/)
144\. Binary Tree Preorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-preorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-preorder-traversal/description/)
```java
public List<Integer> preorderTraversal(TreeNode root) {
@ -572,7 +606,9 @@ public List<Integer> preorderTraversal(TreeNode root) {
## 2. 非递归实现二叉树的后序遍历
[145. Binary Tree Postorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-postorder-traversal/description/)
145\. Binary Tree Postorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-postorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-postorder-traversal/description/)
前序遍历为 root -> left -> right，后序遍历为 left -> right -> root。可以修改前序遍历成为 root -> right -> left，那么这个顺序就和后序遍历正好相反。
@ -595,7 +631,9 @@ public List<Integer> postorderTraversal(TreeNode root) {
## 3. 非递归实现二叉树的中序遍历
[94. Binary Tree Inorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-inorder-traversal/description/)
94\. Binary Tree Inorder Traversal (Medium)
[Leetcode](https://leetcode.com/problems/binary-tree-inorder-traversal/description/) / [力扣](https://leetcode-cn.com/problems/binary-tree-inorder-traversal/description/)
```java
public List<Integer> inorderTraversal(TreeNode root) {
@ -624,7 +662,9 @@ public List<Integer> inorderTraversal(TreeNode root) {
## 1. 修剪二叉查找树
[669. Trim a Binary Search Tree (Easy)](https://leetcode.com/problems/trim-a-binary-search-tree/description/)
669\. Trim a Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/trim-a-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/trim-a-binary-search-tree/description/)
```html
Input:
@ -664,7 +704,9 @@ public TreeNode trimBST(TreeNode root, int L, int R) {
## 2. 寻找二叉查找树的第 k 个元素
[230. Kth Smallest Element in a BST (Medium)](https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/)
230\. Kth Smallest Element in a BST (Medium)
[Leetcode](https://leetcode.com/problems/kth-smallest-element-in-a-bst/description/) / [力扣](https://leetcode-cn.com/problems/kth-smallest-element-in-a-bst/description/)
中序遍历解法：
@ -708,7 +750,9 @@ private int count(TreeNode node) {
## 3. 把二叉查找树每个节点的值都加上比它大的节点的值
[Convert BST to Greater Tree (Easy)](https://leetcode.com/problems/convert-bst-to-greater-tree/description/)
Convert BST to Greater Tree (Easy)
[Leetcode](https://leetcode.com/problems/convert-bst-to-greater-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-bst-to-greater-tree/description/)
```html
Input: The root of a Binary Search Tree like this:
@ -745,7 +789,9 @@ private void traver(TreeNode node) {
## 4. 二叉查找树的最近公共祖先
[235. Lowest Common Ancestor of a Binary Search Tree (Easy)](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/)
235\. Lowest Common Ancestor of a Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-search-tree/description/)
```html
_______6______
@ -769,7 +815,9 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
## 5. 二叉树的最近公共祖先
[236. Lowest Common Ancestor of a Binary Tree (Medium) ](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/)
236\. Lowest Common Ancestor of a Binary Tree (Medium)
[Leetcode](https://leetcode.com/problems/lowest-common-ancestor-of-a-binary-tree/description/) / [力扣](https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/description/)
```html
_______3______
@ -794,7 +842,9 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
## 6. 从有序数组中构造二叉查找树
[108. Convert Sorted Array to Binary Search Tree (Easy)](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/)
108\. Convert Sorted Array to Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/convert-sorted-array-to-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/description/)
```java
public TreeNode sortedArrayToBST(int[] nums) {
@ -813,7 +863,9 @@ private TreeNode toBST(int[] nums, int sIdx, int eIdx){
## 7. 根据有序链表构造平衡的二叉查找树
[109. Convert Sorted List to Binary Search Tree (Medium)](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/)
109\. Convert Sorted List to Binary Search Tree (Medium)
[Leetcode](https://leetcode.com/problems/convert-sorted-list-to-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/convert-sorted-list-to-binary-search-tree/description/)
```html
Given the sorted linked list: [-10,-3,0,5,9],
@ -854,7 +906,9 @@ private ListNode preMid(ListNode head) {
## 8. 在二叉查找树中寻找两个节点，使它们的和为一个给定值
[653. Two Sum IV - Input is a BST (Easy)](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/)
653\. Two Sum IV - Input is a BST (Easy)
[Leetcode](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/) / [力扣](https://leetcode-cn.com/problems/two-sum-iv-input-is-a-bst/description/)
```html
Input:
@ -898,7 +952,9 @@ private void inOrder(TreeNode root, List<Integer> nums) {
## 9. 在二叉查找树中查找两个节点之差的最小绝对值
[530. Minimum Absolute Difference in BST (Easy)](https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/)
530\. Minimum Absolute Difference in BST (Easy)
[Leetcode](https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/) / [力扣](https://leetcode-cn.com/problems/minimum-absolute-difference-in-bst/description/)
```html
Input:
@ -936,7 +992,9 @@ private void inOrder(TreeNode node) {
## 10. 寻找二叉查找树中出现次数最多的值
[501. Find Mode in Binary Search Tree (Easy)](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/)
501\. Find Mode in Binary Search Tree (Easy)
[Leetcode](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/) / [力扣](https://leetcode-cn.com/problems/find-mode-in-binary-search-tree/description/)
```html
1
@ -993,7 +1051,9 @@ Trie，又称前缀树或字典树，用于判断字符串是否存在或者是
## 1. 实现一个 Trie
[208. Implement Trie (Prefix Tree) (Medium)](https://leetcode.com/problems/implement-trie-prefix-tree/description/)
208\. Implement Trie (Prefix Tree) (Medium)
[Leetcode](https://leetcode.com/problems/implement-trie-prefix-tree/description/) / [力扣](https://leetcode-cn.com/problems/implement-trie-prefix-tree/description/)
```java
class Trie {
@ -1055,7 +1115,9 @@ class Trie {
## 2. 实现一个 Trie，用来求前缀和
[677. Map Sum Pairs (Medium)](https://leetcode.com/problems/map-sum-pairs/description/)
677\. Map Sum Pairs (Medium)
[Leetcode](https://leetcode.com/problems/map-sum-pairs/description/) / [力扣](https://leetcode-cn.com/problems/map-sum-pairs/description/)
```html
Input: insert("apple", 3), Output: Null

44
notes/Leetcode 题解 - 贪心思想.md
View File

@ -17,7 +17,9 @@
# 1. 分配饼干
[455. Assign Cookies (Easy)](https://leetcode.com/problems/assign-cookies/description/)
455\. Assign Cookies (Easy)
[Leetcode](https://leetcode.com/problems/assign-cookies/description/) / [力扣](https://leetcode-cn.com/problems/assign-cookies/description/)
```html
Input: [1,2], [1,2,3]
@ -51,7 +53,9 @@ public int findContentChildren(int[] g, int[] s) {
# 2. 不重叠的区间个数
[435. Non-overlapping Intervals (Medium)](https://leetcode.com/problems/non-overlapping-intervals/description/)
435\. Non-overlapping Intervals (Medium)
[Leetcode](https://leetcode.com/problems/non-overlapping-intervals/description/) / [力扣](https://leetcode-cn.com/problems/non-overlapping-intervals/description/)
```html
Input: [ [1,2], [1,2], [1,2] ]
@ -109,7 +113,9 @@ Arrays.sort(intervals, new Comparator<int[]>() {
# 3. 投飞镖刺破气球
[452. Minimum Number of Arrows to Burst Balloons (Medium)](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/description/)
452\. Minimum Number of Arrows to Burst Balloons (Medium)
[Leetcode](https://leetcode.com/problems/minimum-number-of-arrows-to-burst-balloons/description/) / [力扣](https://leetcode-cn.com/problems/minimum-number-of-arrows-to-burst-balloons/description/)
```
Input:
@ -143,7 +149,9 @@ public int findMinArrowShots(int[][] points) {
# 4. 根据身高和序号重组队列
[406. Queue Reconstruction by Height(Medium)](https://leetcode.com/problems/queue-reconstruction-by-height/description/)
406\. Queue Reconstruction by Height(Medium)
[Leetcode](https://leetcode.com/problems/queue-reconstruction-by-height/description/) / [力扣](https://leetcode-cn.com/problems/queue-reconstruction-by-height/description/)
```html
Input:
@ -175,7 +183,9 @@ public int[][] reconstructQueue(int[][] people) {
# 5. 买卖股票最大的收益
[121. Best Time to Buy and Sell Stock (Easy)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/)
121\. Best Time to Buy and Sell Stock (Easy)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock/description/)
题目描述：一次股票交易包含买入和卖出，只进行一次交易，求最大收益。
@ -198,7 +208,9 @@ public int maxProfit(int[] prices) {
# 6. 买卖股票的最大收益 II
[122. Best Time to Buy and Sell Stock II (Easy)](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/)
122\. Best Time to Buy and Sell Stock II (Easy)
[Leetcode](https://leetcode.com/problems/best-time-to-buy-and-sell-stock-ii/description/) / [力扣](https://leetcode-cn.com/problems/best-time-to-buy-and-sell-stock-ii/description/)
题目描述：可以进行多次交易，多次交易之间不能交叉进行，可以进行多次交易。
@ -219,7 +231,9 @@ public int maxProfit(int[] prices) {
# 7. 种植花朵
[605. Can Place Flowers (Easy)](https://leetcode.com/problems/can-place-flowers/description/)
605\. Can Place Flowers (Easy)
[Leetcode](https://leetcode.com/problems/can-place-flowers/description/) / [力扣](https://leetcode-cn.com/problems/can-place-flowers/description/)
```html
Input: flowerbed = [1,0,0,0,1], n = 1
@ -249,7 +263,9 @@ public boolean canPlaceFlowers(int[] flowerbed, int n) {
# 8. 判断是否为子序列
[392. Is Subsequence (Medium)](https://leetcode.com/problems/is-subsequence/description/)
392\. Is Subsequence (Medium)
[Leetcode](https://leetcode.com/problems/is-subsequence/description/) / [力扣](https://leetcode-cn.com/problems/is-subsequence/description/)
```html
s = "abc", t = "ahbgdc"
@ -271,7 +287,9 @@ public boolean isSubsequence(String s, String t) {
# 9. 修改一个数成为非递减数组
[665. Non-decreasing Array (Easy)](https://leetcode.com/problems/non-decreasing-array/description/)
665\. Non-decreasing Array (Easy)
[Leetcode](https://leetcode.com/problems/non-decreasing-array/description/) / [力扣](https://leetcode-cn.com/problems/non-decreasing-array/description/)
```html
Input: [4,2,3]
@ -305,7 +323,9 @@ public boolean checkPossibility(int[] nums) {
# 10. 子数组最大的和
[53. Maximum Subarray (Easy)](https://leetcode.com/problems/maximum-subarray/description/)
53\. Maximum Subarray (Easy)
[Leetcode](https://leetcode.com/problems/maximum-subarray/description/) / [力扣](https://leetcode-cn.com/problems/maximum-subarray/description/)
```html
For example, given the array [-2,1,-3,4,-1,2,1,-5,4],
@ -329,7 +349,9 @@ public int maxSubArray(int[] nums) {
# 11. 分隔字符串使同种字符出现在一起
[763. Partition Labels (Medium)](https://leetcode.com/problems/partition-labels/description/)
763\. Partition Labels (Medium)
[Leetcode](https://leetcode.com/problems/partition-labels/description/) / [力扣](https://leetcode-cn.com/problems/partition-labels/description/)
```html
Input: S = "ababcbacadefegdehijhklij"

40
notes/Leetcode 题解 - 链表.md
View File

@ -16,7 +16,9 @@
# 1. 找出两个链表的交点
[160. Intersection of Two Linked Lists (Easy)](https://leetcode.com/problems/intersection-of-two-linked-lists/description/)
160\. Intersection of Two Linked Lists (Easy)
[Leetcode](https://leetcode.com/problems/intersection-of-two-linked-lists/description/) / [力扣](https://leetcode-cn.com/problems/intersection-of-two-linked-lists/description/)
例如以下示例中 A 和 B 两个链表相交于 c1：
@ -66,7 +68,9 @@ public ListNode getIntersectionNode(ListNode headA, ListNode headB) {
# 2. 链表反转
[206. Reverse Linked List (Easy)](https://leetcode.com/problems/reverse-linked-list/description/)
206\. Reverse Linked List (Easy)
[Leetcode](https://leetcode.com/problems/reverse-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/reverse-linked-list/description/)
递归
@ -100,7 +104,9 @@ public ListNode reverseList(ListNode head) {
# 3. 归并两个有序的链表
[21. Merge Two Sorted Lists (Easy)](https://leetcode.com/problems/merge-two-sorted-lists/description/)
21\. Merge Two Sorted Lists (Easy)
[Leetcode](https://leetcode.com/problems/merge-two-sorted-lists/description/) / [力扣](https://leetcode-cn.com/problems/merge-two-sorted-lists/description/)
```java
public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
@ -118,7 +124,9 @@ public ListNode mergeTwoLists(ListNode l1, ListNode l2) {
# 4. 从有序链表中删除重复节点
[83. Remove Duplicates from Sorted List (Easy)](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/)
83\. Remove Duplicates from Sorted List (Easy)
[Leetcode](https://leetcode.com/problems/remove-duplicates-from-sorted-list/description/) / [力扣](https://leetcode-cn.com/problems/remove-duplicates-from-sorted-list/description/)
```html
Given 1->1->2, return 1->2.
@ -135,7 +143,9 @@ public ListNode deleteDuplicates(ListNode head) {
# 5. 删除链表的倒数第 n 个节点
[19. Remove Nth Node From End of List (Medium)](https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/)
19\. Remove Nth Node From End of List (Medium)
[Leetcode](https://leetcode.com/problems/remove-nth-node-from-end-of-list/description/) / [力扣](https://leetcode-cn.com/problems/remove-nth-node-from-end-of-list/description/)
```html
Given linked list: 1->2->3->4->5, and n = 2.
@ -161,7 +171,9 @@ public ListNode removeNthFromEnd(ListNode head, int n) {
# 6. 交换链表中的相邻结点
[24. Swap Nodes in Pairs (Medium)](https://leetcode.com/problems/swap-nodes-in-pairs/description/)
24\. Swap Nodes in Pairs (Medium)
[Leetcode](https://leetcode.com/problems/swap-nodes-in-pairs/description/) / [力扣](https://leetcode-cn.com/problems/swap-nodes-in-pairs/description/)
```html
Given 1->2->3->4, you should return the list as 2->1->4->3.
@ -189,7 +201,9 @@ public ListNode swapPairs(ListNode head) {
# 7. 链表求和
[445. Add Two Numbers II (Medium)](https://leetcode.com/problems/add-two-numbers-ii/description/)
445\. Add Two Numbers II (Medium)
[Leetcode](https://leetcode.com/problems/add-two-numbers-ii/description/) / [力扣](https://leetcode-cn.com/problems/add-two-numbers-ii/description/)
```html
Input: (7 -> 2 -> 4 -> 3) + (5 -> 6 -> 4)
@ -228,7 +242,9 @@ private Stack<Integer> buildStack(ListNode l) {
# 8. 回文链表
[234. Palindrome Linked List (Easy)](https://leetcode.com/problems/palindrome-linked-list/description/)
234\. Palindrome Linked List (Easy)
[Leetcode](https://leetcode.com/problems/palindrome-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/palindrome-linked-list/description/)
题目要求：以 O(1) 的空间复杂度来求解。
@ -277,7 +293,9 @@ private boolean isEqual(ListNode l1, ListNode l2) {
# 9. 分隔链表
[725. Split Linked List in Parts(Medium)](https://leetcode.com/problems/split-linked-list-in-parts/description/)
725\. Split Linked List in Parts(Medium)
[Leetcode](https://leetcode.com/problems/split-linked-list-in-parts/description/) / [力扣](https://leetcode-cn.com/problems/split-linked-list-in-parts/description/)
```html
Input:
@ -317,7 +335,9 @@ public ListNode[] splitListToParts(ListNode root, int k) {
# 10. 链表元素按奇偶聚集
[328. Odd Even Linked List (Medium)](https://leetcode.com/problems/odd-even-linked-list/description/)
328\. Odd Even Linked List (Medium)
[Leetcode](https://leetcode.com/problems/odd-even-linked-list/description/) / [力扣](https://leetcode-cn.com/problems/odd-even-linked-list/description/)
```html
Example: