46 KiB
46 KiB
- ????? ??????????????
- ?????? ???????????
- ?????? ???????????·
- ?????? ?????????Ч??
- ?????? ?????е????????
- ?????? ???????????
????? ??????????????
2. ??? Singleton
???????
????????У???о???????????????????????????????????????????????????????????о??????????????????????????????????????????????????????????????? if(uniqueInstance == null) ??????飬????????????? uniqueInstance ??о????????
public class Singleton {
private static Singleton uniqueInstance;
private Singleton() {
}
public static Singleton getUniqueInstance() {
if (uniqueInstance == null) {
uniqueInstance = new Singleton();
}
return uniqueInstance;
}
}
???????????????????
?????? getUniqueInstance() ????????????????÷????????????????????????????? uniqueInstance ???????ж?????????????????????????????????????????????????????????????????
public static synchronized Singleton getUniqueInstance() {
if (uniqueInstance == null) {
uniqueInstance = new Singleton();
}
return uniqueInstance;
}
????????????????????
????????????????????????????
private static Singleton uniqueInstance = new Singleton();
????????????????????
????????????????????????? getUniqueInstance() ???????м?????????????????? uniqueInstance = new Singleton(); ?????????????ɡ??????????????????ж? uniqueInstance ???????????????????????????????????
public class Singleton {
private volatile static Singleton uniqueInstance;
private Singleton() {
}
public static synchronized Singleton getUniqueInstance() {
if (uniqueInstance == null) {
synchronized (Singleton.class) {
if (uniqueInstance == null) {
uniqueInstance = new Singleton();
}
}
}
return uniqueInstance;
}
}
3. ???????????????
???????
?????????? n ???????????????????? 0 ?? n-1 ???Χ??? ???????Щ????????????????????м??????????????????????????????????Ρ????????????????????????????? ???磬?????????? 7 ?????? {2, 3, 1, 0, 2, 5, 3}???????????????????????????? 2??
?????·
????????????? [0, n-1] ??Χ?????????????? i ????????? i ??λ?????
public boolean duplicate(int numbers[], int length, int[] duplication) {
for (int i = 0; i < length; i++) {
while (numbers[i] != i && numbers[i] != numbers[numbers[i]]) {
swap(numbers, i, numbers[i]);
}
if (numbers[i] != i && numbers[i] == numbers[numbers[i]]) {
duplication[0] = numbers[i];
return true;
}
}
return false;
}
private void swap(int[] numbers, int i, int j) {
int t = numbers[i];
numbers[i] = numbers[j];
numbers[j] = t;
}
4. ????????е????
???????
?????????????У????ж?????????????????????????ж????????????????????????????????????????????????????????????????????ж???????????и???????
public boolean Find(int target, int [][] array) {
if (array == null || array.length == 0 || array[0].length == 0) return false;
int m = array.length, n = array[0].length;
int row = 0, col = n - 1;
while (row < m && col >= 0) {
if (target == array[row][col]) return true;
else if (target < array[row][col]) col--;
else row++;
}
return false;
}
5. ?滻???
???????
?????????????????????????е????滻?ɡ?%20???????磬???????? We Are Happy. ????滻?????????? We%20Are%20Happy??
??????
?? O(1) ???临????????
public String replaceSpace(StringBuffer str) {
int n = str.length();
for (int i = 0; i < n; i++) {
if (str.charAt(i) == ' ') str.append(" "); // β?????????
}
int idxOfOriginal = n - 1;
int idxOfNew = str.length() - 1;
while (idxOfOriginal >= 0 && idxOfNew > idxOfOriginal) {
if (str.charAt(idxOfOriginal) == ' ') {
str.setCharAt(idxOfNew--, '0');
str.setCharAt(idxOfNew--, '2');
str.setCharAt(idxOfNew--, '%');
} else {
str.setCharAt(idxOfNew--, str.charAt(idxOfOriginal));
}
idxOfOriginal--;
}
return str.toString();
}
6. ??β??????????
????????????? Collections.reverse().
public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
ArrayList<Integer> ret = new ArrayList<>();
while (listNode != null) {
ret.add(listNode.val);
listNode = listNode.next;
}
Collections.reverse(ret);
return ret;
}
???
public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
ArrayList<Integer> ret = new ArrayList<>();
if(listNode != null) {
ret.addAll(printListFromTailToHead(listNode.next));
ret.add(listNode.val);
}
return ret;
}
???????????????????????????????????????巨???????????
public ArrayList<Integer> printListFromTailToHead(ListNode listNode) {
ListNode head = new ListNode(-1); // ????
ListNode cur = listNode;
while (cur != null) {
ListNode next = cur.next;
cur.next = head.next;
head.next = cur;
cur = next;
}
ArrayList<Integer> ret = new ArrayList<>();
head = head.next;
while (head != null) {
ret.add(head.val);
head = head.next;
}
return ret;
}
7. ?????????
???????
??????????????????????????????????????????????
public TreeNode reConstructBinaryTree(int[] pre, int[] in) {
return reConstructBinaryTree(pre, 0, pre.length - 1, in, 0, in.length - 1);
}
private TreeNode reConstructBinaryTree(int[] pre, int preL, int preR, int[] in, int inL, int inR) {
if(preL > preR || inL > inR) return null;
TreeNode root = new TreeNode(pre[preL]);
if (preL != preR) {
int idx = inL;
while (idx <= inR && in[idx] != root.val) idx++;
int leftTreeLen = idx - inL;
root.left = reConstructBinaryTree(pre, preL + 1, preL + leftTreeLen, in, inL, inL + leftTreeLen - 1);
root.right = reConstructBinaryTree(pre, preL + leftTreeLen + 1, preR, in, inL + leftTreeLen + 1, inR);
}
return root;
}
8. ????????????????
???????
??????????????????е???????????????????????????????????????????е????????????????????????????????
public TreeLinkNode GetNext(TreeLinkNode pNode) {
if (pNode == null) return null;
if (pNode.right != null) {
pNode = pNode.right;
while (pNode.left != null) pNode = pNode.left;
return pNode;
} else {
TreeLinkNode parent = pNode.next;
while (parent != null) {
if (parent.left == pNode) return parent;
pNode = pNode.next;
parent = pNode.next;
}
}
return null;
}
9. ?????????????
Stack<Integer> stack1 = new Stack<Integer>();
Stack<Integer> stack2 = new Stack<Integer>();
public void push(int node) {
stack1.push(node);
}
public int pop() {
if (stack2.isEmpty()) {
while (!stack1.isEmpty()) {
stack2.push(stack1.pop());
}
}
return stack2.pop();
}
10.1 ??????????
private int[] fib = new int[40];
public Solution() {
fib[1] = 1;
fib[2] = 2;
for (int i = 2; i < fib.length; i++) {
fib[i] = fib[i - 1] + fib[i - 2];
}
}
public int Fibonacci(int n) {
return fib[n];
}
10.2 ?????
public int JumpFloor(int target) {
if (target == 1) return 1;
int[] dp = new int[target];
dp[0] = 1;
dp[1] = 2;
for (int i = 2; i < dp.length; i++) {
dp[i] = dp[i - 1] + dp[i - 2];
}
return dp[target - 1];
}
10.3 ????????
public int JumpFloorII(int target) {
int[] dp = new int[target];
Arrays.fill(dp, 1);
for (int i = 1; i < target; i++) {
for (int j = 0; j < i; j++) {
dp[i] += dp[j];
}
}
return dp[target - 1];
}
10.4 ???θ???
???????
????????? 2*1 ??С???κ?????????????????????Ρ??????? n ?? 2*1 ??С????????????????? 2*n ?????Σ?????ж??????????
public int RectCover(int target) {
if (target <= 2) return target;
return RectCover(target - 1) + RectCover(target - 2);
}
11. ??????????С????
???????
?????????????????????????????β??????????????????? ??????????????????????????????????????????С???? ???????? {3, 4, 5, 1, 2} ? {1, 2, 3, 4, 5} ???????????????????С?? 1?? NOTE???????????????????? 0?????????С? 0?????? 0??
public int minNumberInRotateArray(int[] array) {
if (array.length == 0) return 0;
for (int i = 0; i < array.length - 1; i++) {
if (array[i] > array[i + 1]) return array[i + 1];
}
return 0;
}
12. ?????е?·??
???????
???????????????????ж????????????????????????????????????????·????·???????????е??????????????????????????????????????????????????????????????????·????????????е?????????????·???????????????? ???? a b c e s f c s a d e e ?????а??????????? "bcced" ??·????????????в????? "abcb" ·????????????????????? b ?????????е????е???????????·????????ν????????
private int[][] next = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
public boolean hasPath(char[] matrix, int rows, int cols, char[] str) {
if (rows == 0 || cols == 0) return false;
char[][] m = new char[rows][cols];
for (int i = 0, idx = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
m[i][j] = matrix[idx++];
}
}
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
if (backtracking(m, rows, cols, str, new boolean[rows][cols], 0, i, j)) return true;
}
}
return false;
}
private boolean backtracking(char[][] m, int rows, int cols, char[] str, boolean[][] used, int path, int r, int c) {
if (path == str.length) return true;
if (r < 0 || r >= rows || c < 0 || c >= cols) return false;
if (m[r][c] != str[path]) return false;
if (used[r][c]) return false;
used[r][c] = true;
for (int i = 0; i < next.length; i++) {
if (backtracking(m, rows, cols, str, used, path + 1, r + next[i][0], c + next[i][1])) return true;
}
used[r][c] = false;
return false;
}
13. ????????????Χ
???????
????????? m ?к? n ?е?????????????????? 0, 0 ?????????????????????????????????????????????????????????????????????λ?????? k ?????? ???磬?? k ? 18 ??????????????????35, 37??????? 3+5+3+7 = 18??????????????????35, 38??????? 3+5+3+8 = 19???????????????????????????
private int cnt = 0;
private int[][] next = {{0, -1}, {0, 1}, {-1, 0}, {1, 0}};
private int[][] digitSum;
public int movingCount(int threshold, int rows, int cols) {
initDigitSum(rows, cols);
dfs(new boolean[rows][cols], threshold, rows, cols, 0, 0);
return cnt;
}
private void dfs(boolean[][] visited, int threshold, int rows, int cols, int r, int c) {
if (r < 0 || r >= rows || c < 0 || c >= cols) return;
if (visited[r][c]) return;
visited[r][c] = true;
if (this.digitSum[r][c] > threshold) return;
this.cnt++;
for (int i = 0; i < this.next.length; i++) {
dfs(visited, threshold, rows, cols, r + next[i][0], c + next[i][1]);
}
}
private void initDigitSum(int rows, int cols) {
int[] digitSumOne = new int[Math.max(rows, cols)];
for (int i = 0; i < digitSumOne.length; i++) {
int n = i;
while (n > 0) {
digitSumOne[i] += n % 10;
n /= 10;
}
}
this.digitSum = new int[rows][cols];
for (int i = 0; i < rows; i++) {
for (int j = 0; j < cols; j++) {
this.digitSum[i][j] = digitSumOne[i] + digitSumOne[j];
}
}
}
14. ??????
???????
?????????????Σ??????????ε?????????
?????·
???????ü?????? 3 ?????????????????г???? 1 ???????????????????????????кó???? 3 ?????????ó????????? 1 ?????????????????????г????γ???? 2 ???????
int maxProductAfterCuttin(int length) {
if (length < 2) return 0;
if (length == 2) return 1;
if (length == 3) return 2;
int timesOf3 = length / 3;
if (length - timesOf3 * 3 == 1) timesOf3--;
int timesOf2 = (length - timesOf3 * 3) / 2;
return (int) (Math.pow(3, timesOf3)) * (int) (Math.pow(2, timesOf2));
}
15. ???????? 1 ?????
public int NumberOf1(int n) {
return Integer.bitCount(n);
}
n&(n-1) ??λ????????? n ??λ??????????????λ???????????????? 10110100????? 1 ??? 10110011???????????????? 10110000??
public int NumberOf1(int n) {
int cnt = 0;
while (n != 0) {
cnt++;
n &= (n - 1);
}
return cnt;
}
?????? ???????????
16. ??????????η?
public double Power(double base, int exponent) {
if (exponent == 0) return 1;
if (exponent == 1) return base;
boolean isNegative = false;
if (exponent < 0) {
exponent = -exponent;
isNegative = true;
}
double pow = Power(base * base, exponent / 2);
if (exponent % 2 != 0) pow = pow * base;
return isNegative ? 1 / pow : pow;
}
18. ????????????????
public ListNode deleteDuplication(ListNode pHead) {
if (pHead == null) return null;
if (pHead.next == null) return pHead;
if (pHead.val == pHead.next.val) {
ListNode next = pHead.next;
while (next != null && pHead.val == next.val) {
next = next.next;
}
return deleteDuplication(next);
} else {
pHead.next = deleteDuplication(pHead.next);
return pHead;
}
}
19. ??????????
???????
?????????????????????? '.' ?? '*' ??????????????е???? '.' ????????????????? '*' ???????????????????????Σ????? 0 ?Σ??? ??????У???????????????????????????????????磬????? "aaa" ???? "a.a" ?? "ab*ac*a" ????????? "aa.a" ?? "ab*a" ???????
public boolean match(char[] str, char[] pattern) {
int n = str.length, m = pattern.length;
boolean[][] dp = new boolean[n + 1][m + 1];
dp[0][0] = true;
for (int i = 1; i <= m; i++) {
if (pattern[i - 1] == '*') dp[0][i] = dp[0][i - 2];
}
for (int i = 1; i <= n; i++) {
for (int j = 1; j <= m; j++) {
if (str[i - 1] == pattern[j - 1] || pattern[j - 1] == '.') dp[i][j] = dp[i - 1][j - 1];
else if (pattern[j - 1] == '*') {
if (pattern[j - 2] != str[i - 1] && pattern[j - 2] != '.') dp[i][j] = dp[i][j - 2];
else dp[i][j] = dp[i][j - 1] || dp[i][j - 2] || dp[i - 1][j];
}
}
}
return dp[n][m];
}
20. ?????????????
???????
?????????????????ж??????????????????????????С?????????磬????? "+100","5e2","-123","3.1416" ?? "-1E-16" ?????????? ???? "12e","1a3.14","1.2.3","+-5" ?? "12e+4.3" ???????
public boolean isNumeric(char[] str) {
String string = String.valueOf(str);
return string.matches("[\\+-]?[0-9]*(\\.[0-9]*)?([eE][\\+-]?[0-9]+)?");
}
21. ????????????????λ????????
??临??? : O(n2) ??临??? : O(1)
public void reOrderArray(int[] array) {
int n = array.length;
for (int i = 0; i < n; i++) {
if (array[i] % 2 == 0) {
int nextOddIdx = i + 1;
while (nextOddIdx < n && array[nextOddIdx] % 2 == 0) nextOddIdx++;
if (nextOddIdx == n) break;
int nextOddVal = array[nextOddIdx];
for (int j = nextOddIdx; j > i; j--) {
array[j] = array[j - 1];
}
array[i] = nextOddVal;
}
}
}
??临??? : O(n) ??临??? : O(n)
public void reOrderArray(int[] array) {
int oddCnt = 0;
for (int num : array) if (num % 2 == 1) oddCnt++;
int[] copy = array.clone();
int i = 0, j = oddCnt;
for (int num : copy) {
if (num % 2 == 1) array[i++] = num;
else array[j++] = num;
}
}
22. ?????е????? k ?????
public ListNode FindKthToTail(ListNode head, int k) {
if (head == null) return null;
ListNode fast, slow;
fast = slow = head;
while (fast != null && k-- > 0) fast = fast.next;
if (k > 0) return null;
while (fast != null) {
fast = fast.next;
slow = slow.next;
}
return slow;
}
23. ?????л????????
public ListNode EntryNodeOfLoop(ListNode pHead) {
if (pHead == null) return null;
ListNode slow = pHead, fast = pHead;
while (fast != null && fast.next != null) {
fast = fast.next.next;
slow = slow.next;
if (slow == fast) {
fast = pHead;
while (slow != fast) {
slow = slow.next;
fast = fast.next;
}
return slow;
}
}
return null;
}
24. ???????
public ListNode ReverseList(ListNode head) {
ListNode newList = new ListNode(-1);
while (head != null) {
ListNode next = head.next;
head.next = newList.next;
newList.next = head;
head = next;
}
return newList.next;
}
25. ????????????????
public ListNode Merge(ListNode list1, ListNode list2) {
ListNode head = new ListNode(-1);
ListNode cur = head;
while (list1 != null && list2 != null) {
if (list1.val < list2.val) {
cur.next = list1;
list1 = list1.next;
} else {
cur.next = list2;
list2 = list2.next;
}
cur = cur.next;
}
if (list1 != null) cur.next = list1;
if (list2 != null) cur.next = list2;
return head.next;
}
26. ???????
public boolean HasSubtree(TreeNode root1, TreeNode root2) {
if (root1 == null || root2 == null) return false;
return isSubtree(root1, root2) || HasSubtree(root1.left, root2) || HasSubtree(root1.right, root2);
}
private boolean isSubtree(TreeNode root1, TreeNode root2) {
if (root1 == null && root2 == null) return true;
if (root1 == null) return false;
if (root2 == null) return true;
if (root1.val != root2.val) return false;
return isSubtree(root1.left, root2.left) && isSubtree(root1.right, root2.right);
}
?????? ???????????·
27. ???????????
public void Mirror(TreeNode root) {
if (root == null) return;
TreeNode t = root.left;
root.left = root.right;
root.right = t;
Mirror(root.left);
Mirror(root.right);
}
28.1 ?????????
boolean isSymmetrical(TreeNode pRoot) {
if (pRoot == null) return true;
return isSymmetrical(pRoot.left, pRoot.right);
}
boolean isSymmetrical(TreeNode t1, TreeNode t2) {
if (t1 == null && t2 == null) return true;
if (t1 == null || t2 == null) return false;
if (t1.val != t2.val) return false;
return isSymmetrical(t1.left, t2.right) && isSymmetrical(t1.right, t2.left);
}
28.2 ????????
private boolean isBalanced = true;
public boolean IsBalanced_Solution(TreeNode root) {
height(root);
return isBalanced;
}
private int height(TreeNode root) {
if (root == null) return 0;
int left = height(root.left);
int right = height(root.right);
if (Math.abs(left - right) > 1) isBalanced = false;
return 1 + Math.max(left, right);
}
29. ??????????
public ArrayList<Integer> printMatrix(int[][] matrix) {
ArrayList<Integer> ret = new ArrayList<>();
int r1 = 0, r2 = matrix.length - 1, c1 = 0, c2 = matrix[0].length - 1;
while (r1 <= r2 && c1 <= c2) {
for (int i = c1; i <= c2; i++) ret.add(matrix[r1][i]);
for (int i = r1 + 1; i <= r2; i++) ret.add(matrix[i][c2]);
if (r1 != r2) for (int i = c2 - 1; i >= c1; i--) ret.add(matrix[r2][i]);
if (c1 != c2) for (int i = r2 - 1; i > r1; i--) ret.add(matrix[i][c1]);
r1++; r2--; c1++; c2--;
}
return ret;
}
30. ???? min ???????
private Stack<Integer> stack = new Stack<>();
private Stack<Integer> minStack = new Stack<>();
private int min = Integer.MAX_VALUE;
public void push(int node) {
stack.push(node);
if (min > node) min = node;
minStack.push(min);
}
public void pop() {
stack.pop();
minStack.pop();
min = minStack.peek();
}
public int top() {
return stack.peek();
}
public int min() {
return minStack.peek();
}
31. ??????????????
public boolean IsPopOrder(int[] pushA, int[] popA) {
int n = pushA.length;
Stack<Integer> stack = new Stack<>();
for (int i = 0, j = 0; i < n; i++) {
stack.push(pushA[i]);
while (j < n && stack.peek() == popA[j]) {
stack.pop();
j++;
}
}
return stack.isEmpty();
}
32.1 ????????????????
public ArrayList<Integer> PrintFromTopToBottom(TreeNode root) {
Queue<TreeNode> queue = new LinkedList<>();
ArrayList<Integer> ret = new ArrayList<>();
if (root == null) return ret;
queue.add(root);
while (!queue.isEmpty()) {
int cnt = queue.size();
for (int i = 0; i < cnt; i++) {
TreeNode t = queue.poll();
if (t.left != null) queue.add(t.left);
if (t.right != null) queue.add(t.right);
ret.add(t.val);
}
}
return ret;
}
32.3 ???????????????
ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
if (pRoot == null) return ret;
Queue<TreeNode> queue = new LinkedList<>();
queue.add(pRoot);
while (!queue.isEmpty()) {
int cnt = queue.size();
ArrayList<Integer> list = new ArrayList<>();
for (int i = 0; i < cnt; i++) {
TreeNode node = queue.poll();
list.add(node.val);
if (node.left != null) queue.add(node.left);
if (node.right != null) queue.add(node.right);
}
ret.add(list);
}
return ret;
}
32.3 ??????????????????
public ArrayList<ArrayList<Integer>> Print(TreeNode pRoot) {
ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
if (pRoot == null) return ret;
Queue<TreeNode> queue = new LinkedList<>();
queue.add(pRoot);
boolean reverse = false;
while (!queue.isEmpty()) {
int cnt = queue.size();
ArrayList<Integer> list = new ArrayList<>();
for (int i = 0; i < cnt; i++) {
TreeNode node = queue.poll();
list.add(node.val);
if (node.left != null) queue.add(node.left);
if (node.right != null) queue.add(node.right);
}
if (reverse) {
Collections.reverse(list);
reverse = false;
} else {
reverse = true;
}
ret.add(list);
}
return ret;
}
33. ??????????????????????
public boolean VerifySquenceOfBST(int[] sequence) {
if (sequence.length == 0) return false;
return verify(sequence, 0, sequence.length - 1);
}
private boolean verify(int[] sequence, int start, int end) {
if (end - start <= 1) return true;
int rootVal = sequence[end];
int cutIdx = start;
while (cutIdx < end) {
if (sequence[cutIdx] > rootVal) break;
cutIdx++;
}
for (int i = cutIdx + 1; i < end; i++) {
if (sequence[i] < rootVal) return false;
}
return verify(sequence, start, cutIdx - 1) && verify(sequence, cutIdx, end - 1);
}
34. ???????к???????·??
private ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
public ArrayList<ArrayList<Integer>> FindPath(TreeNode root, int target) {
dfs(root, target, 0, new ArrayList<>());
return ret;
}
private void dfs(TreeNode node, int target, int curSum, ArrayList<Integer> path) {
if (node == null) return;
curSum += node.val;
path.add(node.val);
if (curSum == target && node.left == null && node.right == null) {
ret.add(new ArrayList(path));
} else {
dfs(node.left, target, curSum, path);
dfs(node.right, target, curSum, path);
}
path.remove(path.size() - 1);
}
35. ????????????
???????
????????????????????????н??????????????????????????????????????????????????????????????????????????? head??????????????????????????е????????????????????????????
???????????????????????????
??????????????? random ??????и????
????????????
public RandomListNode Clone(RandomListNode pHead) {
if (pHead == null) return null;
// ????????
RandomListNode cur = pHead;
while (cur != null) {
RandomListNode node = new RandomListNode(cur.label);
node.next = cur.next;
cur.next = node;
cur = node.next;
}
// ???? random ????
cur = pHead;
while (cur != null) {
RandomListNode clone = cur.next;
if (cur.random != null) {
clone.random = cur.random.next;
}
cur = clone.next;
}
// ???
RandomListNode pCloneHead = pHead.next;
cur = pHead;
while (cur.next != null) {
RandomListNode t = cur.next;
cur.next = t.next;
cur = t;
}
return pCloneHead;
}
36. ???????????????????
???????
????????????????????????????????????????????????????????????κ???????????????н?????????
private TreeNode pre = null;
public TreeNode Convert(TreeNode pRootOfTree) {
if(pRootOfTree == null) return null;
inOrder(pRootOfTree);
while(pRootOfTree.left != null) pRootOfTree = pRootOfTree.left;
return pRootOfTree;
}
private void inOrder(TreeNode node) {
if(node == null) return;
inOrder(node.left);
node.left = pre;
if(pre != null) pre.right = node;
pre = node;
inOrder(node.right);
}
37. ???л???????
private String serizeString = "";
String Serialize(TreeNode root) {
if (root == null) return "#";
return root.val + " " + Serialize(root.left) + " "
+ Serialize(root.right);
}
TreeNode Deserialize(String str) {
this.serizeString = str;
return Deserialize();
}
private TreeNode Deserialize() {
if (this.serizeString.length() == 0) return null;
int idx = this.serizeString.indexOf(" ");
if (idx == -1) return null;
String sub = this.serizeString.substring(0, idx);
this.serizeString = this.serizeString.substring(idx + 1);
if (sub.equals("#")) {
return null;
}
int val = Integer.valueOf(sub);
TreeNode t = new TreeNode(val);
t.left = Deserialize();
t.right = Deserialize();
return t;
}
38. ???????????
???????
???????????? , ????????????????????????????????С?????????????? abc, ??????????? a, b, c ???????г?????????????? abc, acb, bac, bca, cab ?? cba??
private ArrayList<String> ret = new ArrayList<>();
public ArrayList<String> Permutation(String str) {
if (str.length() == 0) return new ArrayList<>();
char[] chars = str.toCharArray();
Arrays.sort(chars);
backtracking(chars, new boolean[chars.length], "");
return ret;
}
private void backtracking(char[] chars, boolean[] used, String s) {
if (s.length() == chars.length) {
ret.add(s);
return;
}
for (int i = 0; i < chars.length; i++) {
if (used[i]) continue;
if (i != 0 && chars[i] == chars[i - 1] && !used[i - 1]) continue; // ????????
used[i] = true;
backtracking(chars, used, s + chars[i]);
used[i] = false;
}
}
?????? ?????????Ч??
39. ?????г??????????????????
public int MoreThanHalfNum_Solution(int[] array) {
int cnt = 1, num = array[0];
for (int i = 1; i < array.length; i++) {
if (array[i] == num) cnt++;
else cnt--;
if (cnt == 0) {
num = array[i];
cnt = 1;
}
}
cnt = 0;
for (int i = 0; i < array.length; i++) {
if (num == array[i]) cnt++;
}
return cnt > array.length / 2 ? num : 0;
}
40. ??С?? K ????
??????С? k ??С?????
??临????O(nlgk) ??临????O(k)
public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {
if (k > input.length || k <= 0) return new ArrayList<>();
PriorityQueue<Integer> pq = new PriorityQueue<>((o1, o2) -> o2 - o1);
for (int num : input) {
pq.add(num);
if (pq.size() > k) {
pq.poll();
}
}
ArrayList<Integer> ret = new ArrayList<>(pq);
return ret;
}
??????????
??临????O(n) ??临????O(1)
public ArrayList<Integer> GetLeastNumbers_Solution(int[] input, int k) {
if (k > input.length || k <= 0) return new ArrayList<>();
int kthSmallest = findKthSmallest(input, k - 1);
ArrayList<Integer> ret = new ArrayList<>();
for (int num : input) {
if(num <= kthSmallest && ret.size() < k) ret.add(num);
}
return ret;
}
public int findKthSmallest(int[] nums, int k) {
int lo = 0;
int hi = nums.length - 1;
while (lo < hi) {
int j = partition(nums, lo, hi);
if (j < k) {
lo = j + 1;
} else if (j > k) {
hi = j - 1;
} else {
break;
}
}
return nums[k];
}
private int partition(int[] a, int lo, int hi) {
int i = lo;
int j = hi + 1;
while (true) {
while (i < hi && less(a[++i], a[lo])) ;
while (j > lo && less(a[lo], a[--j])) ;
if (i >= j) {
break;
}
exch(a, i, j);
}
exch(a, lo, j);
return j;
}
private void exch(int[] a, int i, int j) {
final int tmp = a[i];
a[i] = a[j];
a[j] = tmp;
}
private boolean less(int v, int w) {
return v < w;
}
41.1 ???????е???λ??
???????
??ε????????????е???λ????????????????ж???????????????????λ????????????????????λ???м???????????????????ж??????????????????λ?????????????????????м???????????????
private PriorityQueue<Integer> maxHeap = new PriorityQueue<>((o1, o2) -> o2-o1); // ?????????
private PriorityQueue<Integer> minHeep = new PriorityQueue<>(); // ????????????????????????????????
private int cnt = 0;
public void Insert(Integer num) {
// ??????????????????????
if(cnt % 2 == 0) {
// ????????????????С???????????????????????????????е?????С????С???е????
maxHeap.add(num);
minHeep.add(maxHeap.poll());
} else {
minHeep.add(num);
maxHeap.add(minHeep.poll());
}
cnt++;
}
public Double GetMedian() {
if(cnt % 2 == 0) {
return (maxHeap.peek() + minHeep.peek()) / 2.0;
} else {
return (double) minHeep.peek();
}
}
14.2 ??????е??????????????
???????
?????????????????????????е???????????ε?????????磬???????????????????????? "go" ???????????????ε?????? "g"?????????????ж?????????????google" ???????????????ε?????? "l"??
//Insert one char from stringstream
private int[] cnts = new int[256];
private Queue<Character> queue = new LinkedList<>();
public void Insert(char ch) {
cnts[ch]++;
queue.add(ch);
while (!queue.isEmpty() && cnts[queue.peek()] > 1) {
queue.poll();
}
}
//return the first appearence once char in current stringstream
public char FirstAppearingOnce() {
if (queue.isEmpty()) return '#';
return queue.peek();
}
42. ???????????????
public int FindGreatestSumOfSubArray(int[] array) {
if(array.length == 0) return 0;
int ret = Integer.MIN_VALUE;
int sum = 0;
for(int num : array) {
if(sum <= 0) sum = num;
else sum += num;
ret = Math.max(ret, sum);
}
return ret;
}
43. ?? 1 ?? n ?????? 1 ????????
????ο???Leetcode : 233. Number of Digit One
public int NumberOf1Between1AndN_Solution(int n) {
int cnt = 0;
for (int m = 1; m <= n; m *= 10) {
int a = n / m, b = n % m;
cnt += (a + 8) / 10 * m + (a % 10 == 1 ? b + 1 : 0);
}
return cnt;
}
45. ???????????С????
???????
????????????????飬????????????????????????????????????????????????????????С??????????????????? {3??32??321}??????????????????????????С????? 321323??
public String PrintMinNumber(int[] numbers) {
int n = numbers.length;
String[] nums = new String[n];
for (int i = 0; i < n; i++) nums[i] = numbers[i] + "";
Arrays.sort(nums, (s1, s2) -> (s1 + s2).compareTo(s2 + s1));
String ret = "";
for (String str : nums) ret += str;
return ret;
}
49. ????
???????
??????????? 2??3 ?? 5 ??????????????Ugly Number???????? 6??8 ??????????? 14 ?????????????????? 7?? ?????????? 1 ???????????????????С?????????? N ????????
public int GetUglyNumber_Solution(int index) {
if (index <= 6) return index;
int i2 = 0, i3 = 0, i5 = 0;
int cnt = 1;
int[] dp = new int[index];
dp[0] = 1;
while (cnt < index) {
int n2 = dp[i2] * 2, n3 = dp[i3] * 3, n5 = dp[i5] * 5;
int tmp = Math.min(n2, Math.min(n3, n5));
dp[cnt++] = tmp;
if (tmp == n2) i2++;
if (tmp == n3) i3++;
if (tmp == n5) i5++;
}
return dp[index - 1];
}
50. ????????????ε????λ??
public int FirstNotRepeatingChar(String str) {
int[] cnts = new int[256];
for (int i = 0; i < str.length(); i++) cnts[str.charAt(i)]++;
for (int i = 0; i < str.length(); i++) if (cnts[str.charAt(i)] == 1) return i;
return -1;
}
51. ?????е??????
private long cnt = 0;
public int InversePairs(int[] array) {
mergeSortUp2Down(array, 0, array.length - 1);
return (int) (cnt % 1000000007);
}
private void mergeSortUp2Down(int[] a, int start, int end) {
if (end - start < 1) return;
int mid = start + (end - start) / 2;
mergeSortUp2Down(a, start, mid);
mergeSortUp2Down(a, mid + 1, end);
merge(a, start, mid, end);
}
private void merge(int[] a, int start, int mid, int end) {
int[] tmp = new int[end - start + 1];
int i = start, j = mid + 1, k = 0;
while (i <= mid || j <= end) {
if (i > mid) tmp[k] = a[j++];
else if (j > end) tmp[k] = a[i++];
else if (a[i] < a[j]) tmp[k] = a[i++];
else {
tmp[k] = a[j++];
this.cnt += mid - i + 1; // a[i] > a[j] ????? a[i...mid] ?????? a[j]
}
k++;
}
for (k = 0; k < tmp.length; k++) {
a[start + k] = tmp[k];
}
}
52. ????????????????????
public ListNode FindFirstCommonNode(ListNode pHead1, ListNode pHead2) {
ListNode l1 = pHead1, l2 = pHead2;
while (l1 != l2) {
if (l1 == null) l1 = pHead2;
else l1 = l1.next;
if (l2 == null) l2 = pHead1;
else l2 = l2.next;
}
return l1;
}
?????? ?????е????????
53 ???????????????г???????
public int GetNumberOfK(int[] array, int k) {
int l = 0, h = array.length - 1;
while (l <= h) {
int m = l + (h - l) / 2;
if (array[m] >= k) h = m - 1;
else l = m + 1;
}
int cnt = 0;
while (l < array.length && array[l++] == k) cnt++;
return cnt;
}
54. ????????????? k ?????
TreeNode ret;
int cnt = 0;
TreeNode KthNode(TreeNode pRoot, int k) {
inorder(pRoot, k);
return ret;
}
private void inorder(TreeNode root, int k) {
if (root == null) return;
if (cnt > k) return;
inorder(root.left, k);
cnt++;
if (cnt == k) ret = root;
inorder(root.right, k);
}
55 ???????????
public int TreeDepth(TreeNode root) {
if (root == null) return 0;
return 1 + Math.max(TreeDepth(root.left), TreeDepth(root.right));
}
56. ?????????????ε?????
???????
???????????????????????????????????????????????Σ??????????????
?????·
???????????????λ??????????????λ????????
??????????????????????????????????????????????????
diff &= -diff ????? diff ?????? 0 ??λ??????????????????????????λ??????????????????λ?????????λ??????????????????????
public void FindNumsAppearOnce(int[] array, int num1[], int num2[]) {
int diff = 0;
for (int num : array) diff ^= num;
// ????????λ
diff &= -diff;
for (int num : array) {
if ((num & diff) == 0) num1[0] ^= num;
else num2[0] ^= num;
}
}
57.1 ??? S ??????????
???????
???????????????????????????? S?????????в?????????????????????????? S??????ж??????????? S?????????????????С???
public ArrayList<Integer> FindNumbersWithSum(int[] array, int sum) {
int i = 0, j = array.length - 1;
while (i < j) {
int cur = array[i] + array[j];
if (cur == sum) return new ArrayList<Integer>(Arrays.asList(array[i], array[j]));
else if (cur < sum) i++;
else j--;
}
return new ArrayList<Integer>();
}
57.2 ??? S ??????????????
???????
??? 100 ???????????? 18, 19, 20, 21, 22
public ArrayList<ArrayList<Integer>> FindContinuousSequence(int sum) {
ArrayList<ArrayList<Integer>> ret = new ArrayList<>();
int start = 1, end = 2;
int mid = sum / 2;
int curSum = 3;
while (start <= mid && end < sum) {
if (curSum > sum) {
curSum -= start;
start++;
} else if (curSum < sum) {
end++;
curSum += end;
} else {
ArrayList<Integer> list = new ArrayList<>();
for (int i = start; i <= end; i++) {
list.add(i);
}
ret.add(list);
curSum -= start;
start++;
end++;
curSum += end;
}
}
return ret;
}
58.1 ????????????
???????
????"I am a student."
?????"student. a am I"
public String ReverseSentence(String str) {
if (str.length() == 0) return str;
int n = str.length();
char[] chars = str.toCharArray();
int start = 0, end = 0;
while (end <= n) {
if (end == n || chars[end] == ' ') {
reverse(chars, start, end - 1);
start = end + 1;
}
end++;
}
reverse(chars, 0, n - 1);
return new String(chars);
}
private void reverse(char[] c, int start, int end) {
while (start < end) {
char t = c[start];
c[start] = c[end];
c[end] = t;
start++;
end--;
}
}
58.2 ??????????
???????
???????????????????? S???????????????? K λ???????????????磬??????? S=??abcXYZdef??, ????????????? 3 λ???????????XYZdefabc????
public String LeftRotateString(String str, int n) {
if (str.length() == 0) return "";
char[] c = str.toCharArray();
reverse(c, 0, n - 1);
reverse(c, n, c.length - 1);
reverse(c, 0, c.length - 1);
return new String(c);
}
private void reverse(char[] c, int i, int j) {
while (i < j) {
char t = c[i];
c[i] = c[j];
c[j] = t;
i++;
j--;
}
}
59. ?????????????
???????
?????????????????????С????????л???????????????????????磬??????????? {2, 3, 4, 2, 6, 2, 5, 1} ????????????С 3???????????? 6 ???????????????????????? {4, 4, 6, 6, 6, 5}??
public ArrayList<Integer> maxInWindows(int[] num, int size) {
ArrayList<Integer> ret = new ArrayList<>();
if (size > num.length || size < 1) return ret;
PriorityQueue<Integer> heap = new PriorityQueue<Integer>((o1, o2) -> o2 - o1);
for (int i = 0; i < size; i++) heap.add(num[i]);
ret.add(heap.peek());
for (int i = 1; i + size - 1 < num.length; i++) {
heap.remove(num[i - 1]);
heap.add(num[i + size - 1]);
ret.add(heap.peek());
}
return ret;
}
61. ????????
???????
??????????д?С????????????С? 0???ж?????????????
public boolean isContinuous(int[] numbers) {
if (numbers.length < 5) return false;
Arrays.sort(numbers);
int cnt = 0;
for (int num : numbers) if (num == 0) cnt++;
for (int i = cnt; i < numbers.length - 1; i++) {
if (numbers[i + 1] == numbers[i]) return false;
int cut = numbers[i + 1] - numbers[i] - 1;
if (cut > cnt) return false;
cnt -= cut;
}
return true;
}
62. ?????????????
???????
??С??????Χ????????????? , ????????????? m, ????? 0 ??С??????????????κ??? m-1 ?????С????????г???? , ??????????????????????????? , ???????????? , ???????????С?????? , ???? 0...m-1 ???? .... ??????? .... ????????????С???? , ???????????
?????·
????
public int LastRemaining_Solution(int n, int m) {
if (n == 0) return -1;
if (n == 1) return 0;
return (LastRemaining_Solution(n - 1, m) + m) % n;
}
63. ????????????
???????
???????????????????????????????????????????档
public int maxProfit(int[] prices) {
int n = prices.length;
if(n == 0) return 0;
int soFarMin = prices[0];
int max = 0;
for(int i = 1; i < n; i++) {
if(soFarMin > prices[i]) soFarMin = prices[i];
else max = Math.max(max, prices[i] - soFarMin);
}
return max;
}
64. ?? 1+2+3+...+n
???????
?? 1+2+3+...+n?????????ó??????for??while??if??else??switch??case ????????????ж????A?B:C??
public int Sum_Solution(int n) {
if(n == 0) return 0;
return n + Sum_Solution(n - 1);
}
65. ???ü??????????
a ^ b ?????п????λ???????????????(a & b) << 1 ?????λ???????????????? (a & b) << 1 ?????????? 0???????????飬??λ?????? 0 ??????????????λ???? 0??????????
public int Add(int num1, int num2) {
if(num2 == 0) return num1;
return Add(num1 ^ num2, (num1 & num2) << 1);
}
66. ???????????
???????
??????????? A[0, 1,..., n-1], ??????????? B[0, 1,..., n-1], ???? B ?е???? B[i]=A[0]*A[1]*...*A[i-1]*A[i+1]*...*A[n-1]????????ó?????
public int[] multiply(int[] A) {
int n = A.length;
int[][] dp = new int[n][n];
for (int i = 0; i < n; i++) {
dp[i][i] = A[i];
}
for (int i = 0; i < n; i++) {
for (int j = i + 1; j < n; j++) {
dp[i][j] = dp[i][j - 1] * A[j];
}
}
int[] B = new int[n];
Arrays.fill(B, 1);
for (int i = 0; i < n; i++) {
if (i != 0) B[i] *= dp[0][i - 1];
if (i != n - 1) B[i] *= dp[i + 1][n - 1];
}
return B;
}
?????? ???????????
67. ????????????????
public int StrToInt(String str) {
if (str.length() == 0) return 0;
char[] chars = str.toCharArray();
boolean isNegative = chars[0] == '-';
int ret = 0;
for (int i = 0; i < chars.length; i++) {
if (i == 0 && (chars[i] == '+' || chars[i] == '-')) continue;
if (chars[i] < '0' || chars[i] > '9') return 0;
ret = ret * 10 + (chars[i] - '0');
}
return isNegative ? -ret : ret;
}
68. ??????????????????????
????????????????????????????
public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
if(root.val > p.val && root.val > q.val) return lowestCommonAncestor(root.left, p, q);
if(root.val < p.val && root.val < q.val) return lowestCommonAncestor(root.right, p, q);
return root;
}