From 528a6bcec710c83abf14b33db35b8e462a07183b Mon Sep 17 00:00:00 2001 From: CyC2018 <1029579233@qq.com> Date: Fri, 9 Mar 2018 13:26:09 +0800 Subject: [PATCH] auto commit --- notes/Leetcode 题解.md | 107 +++++++++++++++++++++++++++++++++++------ 1 file changed, 92 insertions(+), 15 deletions(-) diff --git a/notes/Leetcode 题解.md b/notes/Leetcode 题解.md index e5d3a5ee..8e9fdbba 100644 --- a/notes/Leetcode 题解.md +++ b/notes/Leetcode 题解.md @@ -4260,16 +4260,16 @@ public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) { } ``` -**最大相同节点值的路径长度** +**相同节点值的最大路径长度** -[Leetcode : 687. Longest Univalue Path (Easy)](https://pomotodo.com/app/) +[Leetcode : 687. Longest Univalue Path (Easy)](https://leetcode.com/problems/longest-univalue-path/) ```html - 1 + 1 / \ - 4 5 - / \ \ - 4 4 5 + 4 5 + / \ \ + 4 4 5 Output : 2 ``` @@ -4296,6 +4296,15 @@ private int dfs(TreeNode root){ [Leetcode : 337. House Robber III (Medium)](https://leetcode.com/problems/house-robber-iii/description/) +```html + 3 + / \ + 2 3 + \ \ + 3 1 +Maximum amount of money the thief can rob = 3 + 3 + 1 = 7. +``` + ```java public int rob(TreeNode root) { if (root == null) return 0; @@ -4313,9 +4322,9 @@ public int rob(TreeNode root) { ### 层次遍历 -使用 BFS，不需要使用两个队列来分别存储当前层的节点和下一层的节点， 因为在开始遍历一层的节点时，当前队列中的节点数就是当前层的节点数，只要控制遍历这么多节点数，就能保证这次遍历的都是当前层的节点。 +使用 BFS 进行层次遍历。不需要使用两个队列来分别存储当前层的节点和下一层的节点，因为在开始遍历一层的节点时，当前队列中的节点数就是当前层的节点数，只要控制遍历这么多节点数，就能保证这次遍历的都是当前层的节点。 -**计算一棵树每层节点的平均数** +**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/) @@ -4344,6 +4353,21 @@ public List averageOfLevels(TreeNode root) { [Leetcode : 513. Find Bottom Left Tree Value (Easy)](https://leetcode.com/problems/find-bottom-left-tree-value/description/) +```html +Input: + + 1 + / \ + 2 3 + / / \ + 4 5 6 + / + 7 + +Output: +7 +``` + ```java public int findBottomLeftValue(TreeNode root) { Queue queue = new LinkedList<>(); @@ -4426,9 +4450,9 @@ public List preorderTraversal(TreeNode root) { } ``` -**非递归实现二叉树的后续遍历** +**非递归实现二叉树的后序遍历** -[Leetcode : ### 145. Binary Tree Postorder Traversal (Medium)](https://leetcode.com/problems/binary-tree-postorder-traversal/description/) +[Leetcode : 145. Binary Tree Postorder Traversal (Medium)](https://leetcode.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。 @@ -4471,15 +4495,26 @@ public List inorderTraversal(TreeNode root) { } ``` -**使用中序遍历和前序遍历序列重建二叉树** //TODO - ### BST 主要利用 BST 中序遍历有序的特点。 -**在 BST 中寻找两个节点，使它们的和为一个给定值。** +**在 BST 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](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/) +[653. Two Sum IV - Input is a BST (Easy)](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/description/) + +```html +Input: + 5 + / \ + 3 6 + / \ \ +2 4 7 + +Target = 9 + +Output: True +``` 使用中序遍历得到有序数组之后，再利用双指针对数组进行查找。 @@ -4507,10 +4542,22 @@ private void inOrder(TreeNode root, List nums){ } ``` -**在 BST 中查找最小的两个节点之差的绝对值** +**在 BST 中查找两个节点之差的最小绝对值** [Leetcode : 530. Minimum Absolute Difference in BST (Easy)](https://leetcode.com/problems/minimum-absolute-difference-in-bst/description/) +```html +Input: + 1 + \ + 3 + / + 2 + +Output: +1 +``` + 利用 BST 的中序遍历为有序的性质，计算中序遍历中临近的两个节点之差的绝对值，取最小值。 ```java @@ -4535,6 +4582,18 @@ private void inorder(TreeNode node){ [Leetcode : Convert BST to Greater Tree (Easy)](https://leetcode.com/problems/convert-bst-to-greater-tree/description/) +```html +Input: The root of a Binary Search Tree like this: + 5 + / \ + 2 13 + +Output: The root of a Greater Tree like this: + 18 + / \ + 20 13 +``` + 先遍历右子树。 ```java @@ -4562,6 +4621,17 @@ private void traver(TreeNode root) { **寻找 BST 中出现次数最多的节点** +[Leetcode : 501. Find Mode in Binary Search Tree (Easy)](https://leetcode.com/problems/find-mode-in-binary-search-tree/description/) + +```html + 1 + \ + 2 + / + 2 +return [2]. +``` + ```java private int cnt = 1; private int maxCnt = 1; @@ -4711,6 +4781,13 @@ class Trie { [Leetcode : 677. Map Sum Pairs (Medium)](https://leetcode.com/problems/map-sum-pairs/description/) +```html +Input: insert("apple", 3), Output: Null +Input: sum("ap"), Output: 3 +Input: insert("app", 2), Output: Null +Input: sum("ap"), Output: 5 +``` + ```java class MapSum { private class Trie {