哈希表

• 1. Two Sum (Easy)
• 217. Contains Duplicate (Easy)
• 128. Longest Consecutive Sequence (Hard)
• 149. Max Points on a Line (Hard)
• 332. Reconstruct Itinerary (Medium)
• 304. Range Sum Query 2D - Immutable (Medium)
• 560. Subarray Sum Equals K (Medium)
• 503. Next Greater Element II (Medium) Daily Temperature 的变种题。
• 697. (Easy) 如何对数组进行预处理才能正确并快速地计算子数组的长度?
• 594. Longest Harmonious Subsequence (Easy) 最长连续序列的变种题。 哈希or排序双指针
• 287. Find the Duplicate Number (Medium) 寻找丢失数字的变种题。除了标负位置，你还有没有其它算法可以解决这个问题？
  • Floy找圈
• 313. Super Ugly Number (Medium) 尝试使用优先队列解决这一问题。
• 870. Advantage Shuffle (Medium) 如果我们需要比较大小关系，而且同一数字可能出现多次，那么应该用什么数据结构呢？
• 307. Range Sum Query - Mutable (Medium) 前缀和的变种题。好吧我承认，这道题可能有些超纲，你或许需要搜索一下什么是线段树。

链表

• 160. Intersection of Two Linked Lists (Easy) Goolge
• 206. Reverse Linked List (Easy)
• 21. Merge Two Sorted Lists (Easy)
• 83. Remove Duplicates from Sorted List (Easy)
• !19. Remove Nth Node From End of List (Medium)
• 24. Swap Nodes in Pairs (Medium)
• 725. Split Linked List in Parts(Medium)
• 328. Odd Even Linked List (Medium)
• 215. Kth Largest Element in an Array (Medium)
• 148. Sort List (Medium) 利用快慢指针找到链表中点后，可以对链表进行归并排序

栈和队列

• 232. Implement Queue using Stacks (Easy)
• 225. Implement Stack using Queues (Easy)
• 155. Min Stack (Easy)
• 20. Valid Parentheses (Easy)
• 739 . Daily Temperatures (Medium)
• 23 . Merge k Sorted Lists (Hard)
• 218. The Skyline Problem (Hard)
• 239. Sliding Window Maximum (Hard)

树

递归

• 104. Maximum Depth of Binary Tree (Easy)
• 110. Balanced Binary Tree (Easy)
• !543. Diameter of Binary Tree (Easy)
• 111. 二叉树的最小深度
• [xx] 617. Merge Two Binary Trees (Easy)
• 560. Subarray Sum Equals K 前缀法
• !437. Path Sum III (Easy)
• [xx] 572. Subtree of Another Tree (Easy)
• ! 111. Minimum Depth of Binary Tree (Easy)
• 687. Longest Univalue Path (Easy)
• 337. House Robber III (Medium)
• 671. Second Minimum Node In a Binary Tree (Easy)
• 1110. Delete Nodes And Return Forest (Medium)

层次遍历

• 637. Average of Levels in Binary Tree (Easy)
• 513. Find Bottom Left Tree Value (Easy)

前中后序遍历

• 94. Binary Tree Inorder Traversal (Medium)
• 144. Binary Tree Preorder Traversal (Medium)
• 145. Binary Tree Postorder Traversal (Medium)
• 105. Construct Binary Tree from Preorder and Inorder Traversal (Medium)
  • 注意计算前序子树的大小的时候，要把第一个节点考虑进去
• 99. Recover Binary Search Tree (Hard)

BST

• !669. Trim a Binary Search Tree (Easy) 搜索树的定义
• 230. kth Smallest Element in a BST (Medium) 迭代遍历
• 235. Lowest Common Ancestor of a Binary Search Tree (Easy) 搜索树
• 236. Lowest Common Ancestor of a Binary Tree (Medium)
• 108. Convert Sorted Array to Binary Search Tree (Easy)
• 109. Convert Sorted List to Binary Search Tree (Medium) 找中位数
• 653. Two Sum IV - Input is a BST (Easy)
• 530. Minimum Absolute Difference in BST (Easy)
• 501. Find Mode in Binary Search Tree (Easy)

Trie

• 208. Implement Trie (Prefix Tree) (Medium)
• 677. Map Sum Pairs (Medium)

STL

• 146. LRU Cache (Medium)
• 404. Sum of Left Leaves (Easy) 怎么判断一个节点是不是左节点呢？一种可行的方法是，在辅函数里多传一个参数，表示当前节点是不是父节点的左节点。
• 538. Convert BST to Greater Tree (Easy) 尝试利用某种遍历方式来解决此题，每个节点只需遍历一次。
• 889. Construct Binary Tree from Preorder and Postorder Traversal (Medium) 给定任意两种遍历结果，我们都可以重建树的结构。
• 106. Construct Binary Tree from Inorder and Postorder Traversal (Medium) 给定任意两种遍历结果，我们都可以重建树的结构。
• 897. Increasing Order Search Tree (Easy) 把 BST 压成一个链表，务必考虑清楚指针操作的顺序，否则可能会出现环路。
• !450. Delete Node in a BST (Medium) 当寻找到待删节点时，你可以分情况考虑——当前节点是叶节点、只有一个子节点和有两个子节点。建议同时回收内存。
• 380. Insert Delete GetRandom O(1) (Medium) 设计一个插入、删除和随机取值均为 O(1) 时间复杂度的数据结构。
• [] 432. All O‘one Data Structure (Hard) 设计一个 increaseKey，decreaseKey，getMaxKey，getMinKey 均为 O(1) 时间复杂度的数据结构。

双指针

• 633. Sum of Square Numbers (Easy)
• 345. Reverse Vowels of a String (Easy)
• 680. Valid Palindrome II (Easy)
• 141. Linked List Cycle (Easy)
• 524. Longest Word in Dictionary through Deleting (Medium) 归并两个有序数组的变形题 （双指针）
• 88. Merge Sorted Array (Easy)
• 142. Linked List Cycle II (Medium) 算术题
• 76. Minimum Window Substring (Hard)
• 4. Longest Substring with At Most K Distinct Characters (Hard) 需要利用其它数据结构方便统计当前的字符状态。

搜索

BFS

• 1091. Shortest Path in Binary Matrix(Medium)
• 279. Perfect Squares (Medium)
  • 和硬币问题是一样的，不过不过现在硬币需要实时求出来，而且也求不是总数
• 127. Word Ladder (Medium)
• 547. Friend Circles (Medium)

DFS

• 695. Max Area of Island (Medium)
• 200. Number of Islands (Medium)
• 547. Friend Circles (Medium)
• 130. Surrounded Regions (Medium)
• 417. Pacific Atlantic Water Flow (Medium)

Backtracking

• 17. Letter Combinations of a Phone Number (Medium)
• 93. Restore IP Addresses(Medium)
• 79. Word Search (Medium)
• 46. Permutations (Medium)
• 47. Permutations II (Medium)
• 77. Combinations (Medium)
• 39. Combination Sum (Medium)
• 40. Combination Sum II (Medium)
• 216. Combination Sum III (Medium)
• 78. Subsets (Medium)
• 90. Subsets II (Medium)
• 131. Palindrome Partitioning (Medium)
• 37. Sudoku Solver (Hard)
• !51. N-Queens (Hard)
• 934. Shortest Bridge (Medium)
• 126. Word Ladder II (Hard)
• 2. Binary Tree Paths (Easy) 输出二叉树中所有从根到叶子的路径，回溯法使用与否有什么区别？进阶难度
• 3. Permutations II (Medium) 排列题的 follow-up，如何处理重复元素？
• 4. Combination Sum II (Medium) 组合题的 follow-up，如何处理重复元素？
• 6. Minimum Height Trees (Medium)如何将这道题转为搜索类型题？是使用深度优先还是广度优先呢？

贪心思想

• 455. Assign Cookies (Easy) (Google)
• 435. Non-overlapping Intervals (Medium) (Google)
• 452. Minimum Number of Arrows to Burst Balloons (Medium)
• 406. Queue Reconstruction by Height(Medium)
• 121. Best Time to Buy and Sell Stock (Easy) 历史最低点
• 122. Best Time to Buy and Sell Stock II (Easy)
• 392. Is Subsequence (Medium)
• 665. Non-decreasing Array (Easy)
• 53. Maximum Subarray (Easy)
• 135. Candy (Hard)
• 605. Can Place Flowers (Easy)
• 763. Partition Labels (Medium)

字符串

• 242. Valid Anagram (Easy)
• 409. Longest Palindrome (Easy)
• 205. Isomorphic Strings (Easy)
• 647. Palindromic Substrings (Medium)
• 9. Palindrome Number (Easy)
• 696. Count Binary Substrings (Easy)
  • 计数法
• 1. Basic Calculator II (Medium)
• 2. Implement strStr() (Easy)
• 3. Longest Substring Without Repeating Characters (Medium) 计算最长无重复子字符串，同样的，可以利用其它数据结构进行辅助统计。
• 4. Basic Calculator III (Hard) 题目 227 的 follow-up，十分推荐练习。
• 5. Longest Palindromic Substring (Medium) Manacher’s Algorithm，它可以在 O(n)

图

二分图

• 785. Is Graph Bipartite? (Medium)
• 1059. All Paths from Source Lead to Destination (Medium) 虽然使用深度优先搜索可以解决大部分的图遍历问题，但是注意判断是否陷入了环路。
• 1135. Connecting Cities With Minimum Cost (Medium)
• 882. Reachable Nodes In Subdivided Graph (Hard)

拓扑排序

• 207. Course Schedule (Medium)
• 210. Course Schedule II (Medium)

并查集

• 684. Redundant Connection (Medium)

二分查找

• !69. Sqrt(x) (Easy)
• 744. Find Smallest Letter Greater Than Target (Easy)
• 278. First Bad Version (Easy)
  • 找到坏版本后检查一下
• 153. Find Minimum in Rotated Sorted Array (Medium)
• !34. Find First and Last Position of Element in Sorted Array
• 81. Search in Rotated Sorted Array II (Medium)
• 154. Find Minimum in Rotated Sorted Array II (Medium) 旋转数组的变形题之一。
• 540. Single Element in a Sorted Array (Medium) 在出现独立数之前和之后，奇偶位数的值发生了什么变化？
• 4. Median of Two Sorted Arrays (Hard) 需要对两个数组同时进行二分搜索。

分治

• 241. Different Ways to Add Parentheses (Medium)
• 95. Unique Binary Search Trees II (Medium)

数学

• 204. Count Primes (Easy)

进制转换

• 504. Base 7 (Easy)
• 405. Convert a Number to Hexadecimal (Easy)
• 168. Excel Sheet Column Title (Easy)

阶乘

• 172. Factorial Trailing Zeroes (Easy)

字符串加法减法

• 67. Add Binary (Easy)
• 415. Add Strings (Easy)

相遇问题

• 462. Minimum Moves to Equal Array Elements II (Medium) 这道题是笔者最喜欢的 LeetCode 题目之一，需要先推理出怎么样移动是最优的，再考虑如何进行移动。你或许需要一些前些章节讲过的算法。

多数投票问题

• 169. Majority Element (Easy) 如果想不出简单的解决方法，搜索一下 Boyer-Moore Majority Vote 算法吧。

其它

• 367. Valid Perfect Square (Easy)
• 326. Power of Three (Easy)
• 238. Product of Array Except Self (Medium)
• 628. Maximum Product of Three Numbers (Easy)
• 384. Shuffle an Array (Medium)
• 528. Random Pick with Weight (Medium)
• 382. Linked List Random Node (Medium)
• 5. Implement Rand10() Using Rand7() (Medium) 如何用一个随机数生成器生成另一个随机数生成器？你可能需要利用原来的生成器多次。
• 6. Happy Number (Easy) 你可以简单的用一个 while 循环解决这道题，但是有没有更好的解决办法？如果我们把每个数字想象成一个节点，是否可以转化为环路检测？

位运算

• 1. Hamming Distance (Easy)
• 136. Single Number (Easy)
• 268. Missing Number (Easy)
• !260. Single Number III (Medium)
• 190. Reverse Bits (Easy)
• 231. Power of Two (Easy)
• 342. Power of Four (Easy)
• 693. Binary Number with Alternating Bits (Easy)
• 476. Number Complement (Easy)
• 371. Sum of Two Integers (Easy)
• !318. Maximum Product of Word Lengths (Medium)
• !338. Counting Bits (Medium)

数组与矩阵

• 283. Move Zeroes (Easy)
• 566. Reshape the Matrix (Easy)
• 485. Max Consecutive Ones (Easy)
• 240. Search a 2D Matrix II (Medium)
• 378. Kth Smallest Element in a Sorted Matrix ((Medium))
• 645. Set Mismatch (Easy)
• 667. Beautiful Arrangement II (Medium)
• 766. Toeplitz Matrix (Easy)
• 565. Array Nesting (Medium)
• 769. Max Chunks To Make Sorted (Medium)
• 448. Find All Numbers Disappeared in an Array (Easy)
• 48. Rotate Image (Medium)

桶排序

• 215. Kth Largest Element in an Array

荷兰国旗问题

• 75. Sort Colors (Medium)

快速选择

• 347.Top K Frequent Elements (Medium)
• 451. Sort Characters By Frequency (Medium)

动态规划

斐波那契数列

• 70. Climbing Stairs (Easy) 动态规划
• 198. House Robber (Easy)
• 213. House Robber II (Medium)
• 542. 01 Matrix (Medium)
• 221. Maximal Square (Medium)
• 53. Maximum Subarray (Easy) 经典的一维动态规划题目，试着把一维空间优化为常量吧。
• 343. Integer Break (Medium) 分割类型题，先尝试用动态规划求解，再思考是否有更简单的解法。
• 583. Delete Operation for Two Strings (Medium) 最长公共子序列的变种题。
• 646. Maximum Length of Pair Chain (Medium) 最长递增子序列的变种题，同样的，尝试用二分进行加速。
• 376. Wiggle Subsequence (Medium) 最长摆动子序列，通项公式比较特殊，需要仔细思考。

矩阵路径

• 64. Minimum Path Sum (Medium)
• 62. Unique Paths (Medium)

数组区间

• 303. Range Sum Query - Immutable (Easy)
• 413. Arithmetic Slices (Medium)

分割整数

• 279. Perfect Squares(Medium)
• 91. Decode Ways (Medium)

最长递增子序列

• 300. Longest Increasing Subsequence (Medium)
• 376. Wiggle Subsequence (Medium)

最长公共子序列

• 1143. Longest Common Subsequence
• 416. Partition Equal Subset Sum (Medium) 背包问题
• 494. Target Sum (Medium) 注意排查输入的数据问题
• 474. Ones and Zeroes (Medium)
• 322. !Coin Change (Medium)
• 518. !Coin Change 2 (Medium) 本质和爬楼梯是一样的 problem(i) = sum(problem(i-j)), j = 1, 2, 5
  • 选硬币是组合问题，爬楼梯是排列问题，这对子问题有区别
• 139. Word Break (Medium)
• 377. Combination Sum IV (Medium)

股票交易

• 309. Best Time to Buy and Sell Stock with Cooldown(Medium)
• 714. Best Time to Buy and Sell Stock with Transaction Fee (Medium)
• 123. Best Time to Buy and Sell Stock III (Hard)
• 188. Best Time to Buy and Sell Stock IV (Hard) Goolge

字符串编辑

• 72. Edit Distance (Hard)
• 650. 2 Keys Keyboard (Medium)
• 10. Regular Expression Matching (Hard)