哈希

双指针

283. 移动零

class Solution {public void moveZeroes(int[] nums) {int k = 0;for(int i = 0;i < nums.length; i++){if(nums[i] != 0) {nums[k] = nums[i];k++;}}for (int i = k; i < nums.length; i++) {nums[i] = 0;}}
}

class Solution {public void moveZeroes(int[] nums) {int k = 0;for (int i = 0; i < nums.length; i++) {if (nums[i] != 0) {int temp = nums[i];nums[i] = nums[k];nums[k] = temp;k++;}}}
}

11. 盛最多水的容器

class Solution {public int maxArea(int[] height) {int left = 0, right = height.length - 1;int ans = 0;while (left < right) {int area = Math.min(height[left], height[right]) * (right - left);ans = Math.max(ans, area);if (height[left] <= height[right]) {left++;} else {right--;}}return ans;}
}

42. 接雨水

class Solution {public int trap(int[] height) {int left = 0, right = height.length - 1;int leftMax = 0, rightMax = 0;int ans = 0;while (left < right) {leftMax = Math.max(leftMax, height[left]);rightMax = Math.max(rightMax, height[right]);if (height[left] < height[right]) {ans += leftMax - height[left];left++;} else {ans += rightMax - height[right];right--;}}return ans;}
}

滑动窗口

子串

普通数组

矩阵

链表

二叉树

94. 二叉树的中序遍历

/*** Definition for a binary tree node.* public class TreeNode {*     int val;*     TreeNode left;*     TreeNode right;*     TreeNode() {}*     TreeNode(int val) { this.val = val; }*     TreeNode(int val, TreeNode left, TreeNode right) {*         this.val = val;*         this.left = left;*         this.right = right;*     }* }*/
class Solution {public List<Integer> inorderTraversal(TreeNode root) {List<Integer> reusltList = new ArrayList<>();inorderVisited(root, reusltList);return  reusltList;}private void inorderVisited(TreeNode root, List<Integer> reusltList) {if (root == null) {return;}inorderVisited(root.left, reusltList);reusltList.add(root.val);inorderVisited(root.right, reusltList);}
}

class Solution {public List<Integer> inorderTraversal(TreeNode root) {List<Integer> reusltList = new ArrayList<>();inorderVisited(root, reusltList);return  reusltList;}private void inorderVisited(TreeNode root, List<Integer> reusltList) {Stack<TreeNode> stack = new Stack<>();while (root != null || !stack.empty()) {while (root != null) {stack.push(root);root = root.left;}root = stack.pop();reusltList.add(root.val);root = root.right;}}
}

图论

回溯

二分查找

栈

堆

贪心算法

动态规划

70. 爬楼梯

class Solution {public int climbStairs(int n) {int[] dp = new int[n+1];dp[0] = 1;dp[1] = 1;for(int i = 2;i <= n; i++){dp[i] = dp[i-1] + dp[i-2];}return dp[n];}
}

748. 打家劫舍

class Solution {public int rob(int[] nums) {if (nums.length == 0) {return 0;}int len = nums.length;int[] dp = new int[len+1];dp[0] = 0;dp[1] = nums[0];for(int i = 2; i <= len; i++){dp[i] = Math.max(dp[i-1], dp[i-2] + nums[i-1]);}return dp[len];}
}

279. 完全平方数

class Solution {public int numSquares(int n) {int[] dp = new int[n + 1];for(int i = 1; i <= n;i++) {int minn = Integer.MAX_VALUE;for(int j = 1; j * j <= i; j++){minn = Math.min(minn, dp[i - j * j]);}dp[i] = minn + 1;}return dp[n];}
}

322. 零钱兑换

class Solution {public int coinChange(int[] coins, int amount) {int[] dp = new int[amount + 1];Arrays.fill(dp, amount + 1);dp[0] = 0;for (int i = 1; i <= amount; i++) {for (int coin : coins) {if (i < coin) {continue;}dp[i] = Math.min(dp[i], dp[i - coin]);}dp[i] += 1;}return dp[amount] > amount ? -1 : dp[amount];}
}

class Solution {public int coinChange(int[] coins, int amount) {int[] dp = new int[amount + 1];Arrays.fill(dp, amount + 1);dp[0] = 0;for (int i = 1; i <= amount; i++) {for (int coin : coins) {if (i < coin) {continue;}dp[i] = Math.min(dp[i], dp[i - coin] + 1);}}return (dp[amount] == amount + 1) ? -1 : dp[amount];}
}

416. 分割等和子集

class Solution {public boolean canPartition(int[] nums) {if (nums == null || nums.length == 0) {return false;}int len = nums.length;int sum = 0;for (int num : nums) {sum += num;}if (sum % 2 != 0)return false;int target = sum / 2;int[] dp = new int[target + 1];for (int i = 0; i < len; i++) {for (int j = target; j >= nums[i]; j--) {dp[j] = Math.max(dp[j], dp[j - nums[i]] + nums[i]);}if (dp[target] == target) {return true;}}return dp[target] == target;}
}

多维动态规划

技巧

136. 只出现一次的数字

class Solution {public int singleNumber(int[] nums) {int ans = 0;for (int num : nums) {ans ^= num;}return ans;}
}