| 1-Two Sum | Easy | 数学题 + Sum + HashMap |
| 2-AddTwoNumbers | Medium | 链表 + 数组 + 数位相加 |
| 3-Longest Substring Without Repeating Characters | Medium | 字符串 + window + hashset |
| 4-Median Of Two Sorted Arrays | Hard | 数学题 + 特殊问题 |
| 5-Longest Palindromic Substring | Medium | 字符串 + Palindrome + 中心扩散法 |
| 6-ZigZag Conversion | Medium | 字符串 + 实现题 + 暴力找规律 |
| 7-Reverse Integer | Easy | 数学题 + 数位反转 |
| 8-String To Integer | Medium | 数学题 + str转换 |
| 9-Palindrome Number | Easy | 字符串 + Palindrome + 数位反转 |
| 12-Integer To Roman | Medium | 字符串 + 实现题 + 预先定义 |
| 13-Roman To Integer | Easy | 字符串 + 实现题 + 预先定义 + 找定义 |
| 14-Longest Common Prefix | Easy | 字符串 + 基本 + 双重遍历找一致 |
| 15-3 Sum | Medim | 数学题 + Sum + Sliding Window |
| 16-3 Sum Closest | Medium | 数学题 + Sum + Sliding Window |
| 17-LetterCombinationsOfAPhoneNumber | Medium | 回溯法 + 实现题 + index |
| 18-4 Sum | Medium | 数学题 + Sum |
| 19-Remove Nth Node From End Of List | Medium | 链表+ 删除 + 快慢针 |
| 20-ValidParentheses | Easy | 栈 + 平衡符号 |
| 21-Merge Two Sorted Lists | Easy | 链表 + 基本操作 |
| 22-Generate Parentheses | Medium | 回溯法 + 剪枝 |
| 23-Merge K Sorted Lists | Hard | 链表 + 基本操作 |
| 24-Swap Nodes In Pairs | Medium | 链表 + 基本操作 |
| 28-Implement strStr | Easy | 字符串 |
| 29-Divide Two Integers | Medium | 数学题 + 数位运算 + 减法做除法 |
| 31-NextPermutation | Medium | 排序排列 + 找重点位置 |
| 32-Longest Valid Parentheses | Hard | 栈 + 平衡符号 |
| 33-Search In Rotated Sorted Array | Meidum | 二分法 + Rotate |
| 34-Find First And Last Position Of Element In Sorted Array | Medium | 二分法 + 基本 |
| 35-Search Insert Position | Easy | 二分法 + 基本 |
| 38-Count And Say | Easy | 字符串 + 实现题 + 递归 |
| 39-CombinationSum | Medium | 回溯法 + 组合 + index + sum |
| 40-CombinationSumII | Medium | 回溯法 + 组合 + index + sum + 跳重复元素 |
| 42-Trapping Rain Water | Hard | 栈 + 极值迭代 |
| 43-Multiply Strings | Medium | 数学题 + 数位运算 + 竖位相乘法 |
| 45-Jump Game II | Hard | 贪心算法 |
| 46-Permutations | Medium | 回溯法 + 全排列 |
| 47-PermutationsII | Medium | 回溯法 + 全排列 + 有重复元素used |
| 49-Group Anagrams | Medium | 字符串 + anagram + HashMap |
| 50-Pow(x, n) | Medium | 数学题 + 幂 |
| 55-Jump Game | Medium | 贪心算法 |
| 56-Merge Intervals | Medium | 排序排列 + 扫描线思想 |
| 57-Insert Interval | Medium | 排序排列 + 扫描线思想 |
| 58-Length Of Last Word | Easy | 字符串 + 基本 |
| 61-Rotate List | Meidum | 链表 + 基本操作 |
| 62-Unique Paths | Medium | 动态规划 |
| 66-Plus One | Easy | 数学题 + 加法进位 |
| 67-Add Binary | Easy | 数学题 + 数位相加/str转换 |
| 69-Sqrt(x) | Easy | 数学题 + 二分法 |
| 70-Climbing Stairs | Easy | 递归 + Fibonacci |
| 71-Simplify Path | Medium | 栈 + 压栈匹配 |
| 72-Edit Distance | Hard | 动态规划 + 字符串 |
| 74-Search A 2D Matrix | Medium | 二分法 + 数组 |
| 75-Sort Colors | Medium | 排序 + 三指针 |
| 76-Minimum Window Substring | Hard | 字符串 + substring + sliding window |
| 77-Combinations | Medium | 回溯法 + 组合 + index控制 + k |
| 78-Subsets | Medium | 回溯法 + 子集 + index控制 |
| 79-Word Search | Medium | BFS + Flood Fill |
| 81-Search In Rotated Sorted Array II | Meidum | 二分法 + Rotate |
| 82-Remove Duplicates From Sorted List II | Medium | 链表 + 删除 |
| 83-Remove Duplicates From Sorted List | Easy | 链表 + 删除 |
| 84-Largest Rectangle In Histogram | Hard | 栈 + 极值迭代 |
| 86-Partition List | Medium | 链表 + 基本操作 |
| 88-Merge Sorted Array | easy | 排序 + mergeSort |
| 89-Gray Code | Medium | 位运算 + 动态规划 |
| 90-Subsets II | Medium | 回溯法 + 子集 + index控制 + used |
| 92-Reverse Linked List II | Medium | 链表 + 反转 |
| 93-Restore IP Addresses | Medium | 回溯法 + 实现 + index控制 + 内部数位控制 |
| 94-Binary Tree Inorder Traversal | Medium | 树 + 中序遍历模板 |
| 95-Unique Binary Search Trees II | Medium | 树 + 二叉树实现 + DFS + 回溯 |
| 96-Unique Binary Search Trees | Medium | 动态规划 |
| 98-Validate Binary Search Tree | Medium | 树 + 中序遍历 + BST |
| 100-Same Tree | Easy | 树 + 双pre |
| 101-Symmetric Tree | Easy | 树 + 双pre |
| 102-Binary Tree Level Order Traversal | Medium | 树 + 层次遍历模板 |
| 103-Binary Tree Zigzag Level Order Traversal | Medium | 树 + 层次遍历应用 |
| 104-Maximum Depth Of Binary Tree | Easy | 树 + 后序遍历 |
| 105-Construct Binary Tree From Preorder And Inorder Traversal | Medium | 树的实现 |
| 106-Construct Binary Tree From Inorder And Postorder Traversal | Meidum | 树的实现 |
| 107-Binary Tree Level Order Traversal II | Easy | 树 + 层次遍历 |
| 108-Convert Sorted Array To Binary Search Tree | Easy | 树 + 中序遍历的逆序 + 二分递归 |
| 109-Convert Sorted List To Binary Search Tree | Medium | 树 + 中序遍历 + 套用108 |
| 110-Balanced Binary Tree | Easy | 树 + PostOrder |
| 111-Minimum Depth Of Binary Tree | Easy | 树 + 双 |
| 112-Path Sum | Easy | 树 + 双pre |
| 113-Path Sum II | Medium | 树 + Pre Order + 回溯法 + 控制和 |
| 114-Flatten Binary Tree To Linked List | Medium | 树的实现 + preOrder + Stack |
| 116-Populating Next Right Pointers In Each Node | Medium | 树 + 链表 |
| 117-Populating Next Right Pointers In Each Node II | Medium | 树 + 链表 |
| 118-Pascal’s Triangle | Easy | 递归 + 暴力找规律 |
| 119-Pascal’sTriangle II | Easy | 递归 + 暴力找规律 |
| 122-Best Time To Buy And Sell Stock II | Easy | 贪心算法 + 能赚一点是一点 |
| 125-Valid Palindrome | Easy | 字符串 + Palindrome |
| 127-Word Ladder | Medium | 图 + BFS |
| 129-Sum Root To Leaf Numbers | Medium | 树 + 双pre + 数10进制 |
| 130-Surrounded Regions | Medium | 图 + DFS + Flood Fill + 从边界开始 |
| 131-Palindrome Partitioning | Medium | 回溯法 + 实现题 + 子集 + Palindrome判断 |
| 133-Clone Graph | Medium | 图 + BFS + Hashmap |
| 134-Gas Station | Medium | 贪心算法 + 连续和 |
| 136-Single Number | Easy | 位运算 + 异或 |
| 137-Single Number II | Medium | HashMap |
| 138-Copy List With Random Pointer | Medium | 链表 + Hashmap |
| 139-Word Break | Medium | 动态规划 |
| 141-Linked List Cycle | Easy | 链表 + 快慢针 |
| 142-Linked List Cycle II | Medium | 链表 + 快慢针 |
| 143-Reorder List | Medium | 链表 + 综合 |
| 144-Binary Tree Preorder Traversal | Medium | 树 + 先序遍历模板 |
| 145-Binary Tree Postorder Traversal | Hard | 树 + 后序遍历模板 |
| 146-LRU Cache | Medium | 实现题 + HashMap |
| 147-Insertion Sort List | Medium | 链表 + 数组 + InsertionSort |
| 148-Sort List | Medium | 链表 + 数组 + MergeSort |
| 150-Evaluate Reverse Polish Notation | Medium | 栈+ 压栈匹配 + 数学运算 |
| 151-Reverse Words in a String | Easy | 字符串 + 实现题 |
| 153-Find Minimum In Rotated Sorted Array | Medium | 二分法查找 + range |
| 154-Find Minimum In Rotated Sorted Array II | Hard | 二分法查找 + range |
| 155-Min Stack | Easy | 栈 + 基本应用 |
| 156-Binary Tree Upside Down | Medium | 树 + 链表 |
| 157-Read N Characters Given Read4 I | Easy | 字符串 + 实现题 + 空间思路 |
| 159-Longest Substring With At Most Two Distinct Characters | Medium | 字符串 + substring + sliding window |
| 160-Intersection Of Two Linked Lists | Easy | 链表 + 基本操作 |
| 161-One Edit Distance | Meidum | 字符串 + Substring |
| 162-Find Peak Element | Medium | 二分法查找 + range |
| 165-Compare Version Numbers | Medium | 字符串 + 基本操作 |
| 166-Fraction To Recurring Decimal | Medium | 数学题 + 特殊问题 |
| 167-Two Sum II | Easy | 数学题 + Sum |
| 168-Excel Sheet Column Title | Easy | 字符串 + 基本操作 |
| 170-Two Sum III-Data Structure Design | Easy | 实现题 + HashMap |
| 171-Excel Sheet Column Number | Easy | 字符串 + 基本 + 26进制转换 |
| 172-Factorial Trailing Zeroes | Easy | 数学题 + 特殊问题 |
| 173-Binary Search Tree Iterator | Medium | 树 + 中序遍历应用 |
| 179-Largest Number | Medium | 字符串 + 实现题 + 自定义排序 |
| 187-Repeated DNA Sequences | Medium | 字符串 + substring + hashset |
| 186-Reverse Words In A String II | Medium | 字符串 + 实现题 + 先全部反转再单词内部反转 |
| 190-Reverse Bits | Easy | 位运算 + 按位与 |
| 191-Number Of 1 Bits | Easy | 位运算 + 按位与 |
| 199-Binary Tree Right Side View | Medium | 树 + 层次遍历 |
| 200-Number Of Islands | Medium | 图 + DFS + Flood Fill |
