| 1. Two Sum | Solution | Easy | Array / Hash Table |
| 2. Add Two Numbers | Solution | Medium | Linked List |
| 3. Longest Substring Without Repeating Characters | Solution | Medium | Hash Table / Two Pointers |
| 4. Median of Two Sorted Arrays | Solution | Hard | Array / Binary Search |
| 5. Longest Palindromic Substring | Solution | Medium | String |
| 6. ZigZag Conversion | Solution | Medium | String |
| 7. Reverse_Integer | Solution | Medium | Math |
| 8. StringToInteger | Solution | Medium | String |
| 9. Palindrome Number | Solution | Easy | Math |
| 10. Regular Expression Matching | Solution | Hard | String / Dynamic Programming / Backtracking |
| 11. Container With Most Water | Solution | Medium | Medium |
| 12. Integer to Roman | Solution | Medium | String |
| 13. Roman to Integer | Solution | Easy | String |
| 14. Longest Common Prefix | Solution | Easy | String |
| 15. 3Sum | Solution | Medium | Array / Two Pointers |
| 16. 3Sum Closest | Solution | Medium | Array / Two Pointers |
| 17. Letter Combinations of a Phone Number | Solution | Medium | Backtracking / String |
| 18. 4Sum | Solution | Medium | Array |
| 19. Remove Nth Node From End of List | Solution | Medium | Linked List / Two Pointers |
| 20. Valid Parentheses | Solution | Easy | Stack |
| 21. Merge Two Sorted Lists | Solution | Easy | Linked List |
| 22. Generate Parentheses | Solution | Medium | String / Backtracking |
| 23. Merge k Sorted Lists | Solution | Hard | Linked List / Heap |
| 25. Reverse Nodes in k-Group | Solution | Hard | Linked List |
| 26. Remove Duplicates from Sorted Array | Solution | Easy | Array / Two Pointers |
| 28. Implement strStr() | Solution | Easy | String |
| 29. Divide Two Integers | Solution | Easy | String |
| 31. Next Permutation | Solution | Medium | Array |
| 32. Longest Valid Parentheses | Solution | Hard | |
| 33. Search in Rotated Sorted Array | Solution | Medium | Array / Binary Search |
| 34. Search for a Range | Solution | Medium | Array / Binary Search |
| 35. Search Insert Position | Solution | Easy | Array / Binary Search |
| 36. Valid Sudoku | Solution | Medium | Hash Table |
| 37. Sudoku Solver | Solution | Hard | Hash Table |
| 39. Combination Sum | Solution | Medium | String |
| 41. First Missing Positive | Solution | Hard | Array |
| 42. Trapping Rain Water | Solution | Hard | Array / Two Pointers / Stack |
| 43. Multiply Strings | Solution | Medium | String |
| 44. Wildcard Matching | Solution | Hard | String / Backtracking / Greedy |
| 45. Jump Game II | Solution | Hard | Hard |
| 46. Permutations | Solution | Medium | Backtracking |
| 47. Permutations II | Solution | Medium | Backtracking |
| 48. Rotate Image | Solution | Medium | Matrix |
| 49. Group Anagrams | Solution | Medium | Hash Table / String |
| 50. Pow(x, n) | Solution | Medium | Binary Search |
| 51. N-Queens | Solution | Hard | Binary Search |
| 52. N-Queens II | Solution | Hard | Binary Search |
| 53. Maximum Subarray | Solution | Easy | Dynamic Programming / Array |
| 54. Spiral Matrix | Solution | Medium | Array |
| 55. Jump Game | Solution | Medium | Array / Greedy |
| 56. Merge Intervals | Solution | Medium | Medium |
| 57. Insert Interval | Solution | Hard | Hard |
| 59. Spiral Matrix II | Solution | Medium | Array |
| 60. Permutation Sequence | Solution | Medium | Backtracking / Math |
| 61. Rotate List | Solution | Medium | Linked List / Two Pointers |
| 62. Unique Paths | Solution | Medium | Array / Dynamic Programming |
| 63. Unique Paths II | Solution | Medium | Medium |
| 64. Minimum Path Sum | Solution | Medium | Array / Dynamic Programming |
| 65. Valid Number | Solution | Hard | Array / Dynamic Programming |
| 66. Plus One | Solution | Easy | Array / Math |
| 68. Text Justification | Solution | Hard | String |
| 69. Sqrt(x) | Solution | Easy | Binary Search / Math |
| 70. Climbing Stairs | Solution | Easy | Dynamic Programming |
| 71. Simplify Path | Solution | Medium | Stack / String |
| 72. Edit Distance | Solution | Hard | Stack / String |
| 73. Set Matrix Zeroes | Solution | Medium | Array |
| 74. Search a 2D Matrix | Solution | Medium | Array / Binary Search |
| 75. Sort Colors | Solution | Medium | Array / Two Pointers |
| 76. Minimum Window Substring | Solution | Hard | Hash Table / Two pointers / String |
| 78. Subsets | Solution | Medium | Array / Backtracking |
| 79. Word Search | Solution | Medium | Matrix / Backtracking |
| 80. Remove Duplicates from Sorted Array II | Solution | Medium | Array / Two Pointers |
| 81. Search in Rotated Sorted Array II | Solution | Medium | |
| 82. Remove Duplicates from Sorted List II | Solution | Medium | Linked List |
| 83. Remove Duplicates from Sorted List | Solution | Easy | Linked List |
| 84. Largest Rectangle in Histogram | Solution | Hard | Array |
| 85. Maximal Rectangle | Solution | Hard | Array |
| 86. Partition List | Solution | Medium | Linked List |
| 88. Merge Sorted Array | Solution | Easy | Array / Two Pointers |
| 90. Subsets II | Solution | Medium | Array / Backtracking |
| 91. Decode Ways | Solution | Medium | Dynamic Programming / String |
| 92. Reverse Linked List II | Solution | Medium | Linked List |
| 93. Restore IP Addresses | Solution | Medium | |
| 94. Binary Tree Inorder Traversal | Solution | Medium | Tree / Stack |
| 95. Unique Binary Search Trees II | Solution | Medium | Tree |
| 96. Unique Binary Search Trees | Solution | Medium | Tree / DFS |
| 97. Interleaving String | Solution | Hard | Tree / DFS |
| 98. Validate Binary Search Tree | Solution | Medium | Tree |
| 100. Same Tree | Solution | Easy | Tree / DFS |
| 101. Symmetric Tree | Solution | Easy | Tree |
| 102. Binary Tree Level Order Traversal | Solution | Medium | Tree / DFS / BFS |
| 103. Binary Tree Zigzag Level Order Traversal | Solution | Medium | Tree / BFS |
| 104. Maximum Depth of Binary Tree | Solution | Easy | Tree |
| 105. Construct Binary Tree from Preorder and Inorder Traversal | Solution | Medium | Array / Tree / DFS |
| 106. Construct Binary Tree from Inorder and Postorder Traversal | Solution | Medium | Linked List / DFS |
| 107. Binary Tree Level Order Traversal II | Solution | Easy | Tree |
| 108. Convert Sorted Array to Binary Search Tree | Solution | Easy | Tree / DFS |
| 109. Convert Sorted List to Binary Search Tree | Solution | Medium | Linked List / DFS |
| 110. Balanced Binary Tree | Solution | Easy | Tree / DFS |
| 111. Minimum Depth of Binary Tree | Solution | Easy | Tree |
| 112. Path Sum | Solution | Easy | Tree / DFS |
| 113. Path Sum II | Solution | Medium | Tree / DFS |
| 114. Flatten Binary Tree to Linked List | Solution | Medium | Tree / DFS |
| 116. Populating Next Right Pointers in Each Node | Solution | Medium | Tree / BFS |
| 117. Populating Next Right Pointers in Each Node II | Solution | Medium | Tree / Level-order Traversal |
| 119. Pascal's Triangle II | Solution | Easy | Array |
| 120. Triangle | Solution | Medium | Array / Dynamic Programming |
| 121. Best Time to Buy and Sell Stock | Solution | Easy | Array / Dynamic Programming |
| 122. Best Time to Buy and Sell Stock II | Solution | Easy | Tree / DFS |
| 123. Best Time to Buy and Sell Stock III | Solution | Hard | Tree / DFS |
| 124. Binary Tree Maximum Path Sum | Solution | Hard | Tree / DFS |
| 125. Valid Palindrome | Solution | Easy | String / Two Pointers |
| 126. Word Ladder II | Solution | Hard | Array / Unoin Find |
| 127. Word Ladder | Solution | Medium | String / BFS |
| 128. Longest Consecutive Sequence | Solution | Hard | Array / Unoin Find |
| 129. Sum Root to Leaf Numbers | Solution | Medium | Tree / DFS / BFS |
| 130. Surrounded Regions | Solution | Medium | DFS / BFS / Union Find |
| 131. Palindrome Partitioning | Solution | Medium | Backtracking |
| 133. Clone Graph | Solution | Medium | Graph / DFS / BFS |
| 136. Single Number | Solution | Easy | Bit Manipulation |
| 137. Single Number II | Solution | Medium | Dynamic Programming |
| 138. Copy List with Random Pointer | Solution | Medium | Hash Table / Linked List |
| 139. Word Break | Solution | Medium | Dynamic Programming |
| 140. Word Break II | Solution | Hard | Dynamic Programming |
| 141. Linked List Cycle | Solution | Easy | Linked List / Two Pointers |
| 142. Linked List Cycle II | Solution | Easy | Linked List / Two Pointers |
| 143. Reorder List | Solution | Medium | Linked List |
| 144. Binary Tree Preorder Traversal | Solution | Medium | Tree / Stack |
| 146. LRU Cache | Solution | Hard | Design |
| 147. Insertion Sort List | Solution | Medium | Stack / Design |
| 148. Sort List | Solution | Medium | Stack / Design |
| 149. Max Points on a Line | Solution | Hard | Stack / Design |
| 150. Evaluate Reverse Polish Notation | Solution | Medium | |
| 151. Reverse Words in a String | Solution | Medium | String |
| 152. Maximum Product Subarray | Solution | Medium | String / Two Pointers |
| 153. Find Minimum in Rotated Sorted Array | Solution | Medium | String / Two Pointers |
| 154. Find Minimum in Rotated Sorted Array II | Solution | Hard | String / Two Pointers |
| 155. Min Stack | Solution | Easy | Stack / Design |
| 157. Read N Characters Given Read4 | Solution | Easy | String |
| 158. Read N Characters Given Read4 II - Call multiple times | Solution | Hard | String |
| 159. Longest Substring with At Most Two Distinct Characters | Solution | Hard | String / Two Pointers |
| 160. Intersection of Two Linked Lists | Solution | Easy | String |
| 161. One Edit Distance | Solution | Medium | String |
| 162. Find Peak Element | Solution | Medium | Binary Search |
| 163. Missing Ranges | Solution | Medium | Array |
| 165. Compare Version Numbers | Solution | Medium | |
| 166. Fraction to Recurring Decimal | Solution | Medium | |
| 167. Two Sum II - Input array is sorted | Solution | Easy | |
| 169. Majority Element | Solution | Easy | Array |
| 173. Binary Search Tree Iterator | Solution | Medium | Tree / Stack / Design |
| 179. Largest Number | Solution | Medium | |
| 186. Reverse Words in a String II | Solution | Easy | String |
| 187. Repeated DNA Sequences | Solution | Medium | |
| 188. Best Time to Buy and Sell Stock IV | Solution | Hard | |
| 189. Rotate Array | Solution | Easy | |
| 198. House Robber | Solution | Easy | Dynamic Programming |
| 199. Binary Tree Right Side View | Solution | Medium | |
| 200. Number of Islands | Solution | Medium | BFS / Union Find |
| 201. Bitwise AND of Numbers Range | Solution | Medium | |
| 202. Happy Number | Solution | Easy | |
| 203. Remove Linked List Elements | Solution | Easy | |
| 204. Count Primes | Solution | Easy | |
| 205. Isomorphic Strings | Solution | Easy | Hash Table |
| 206. Reverse Linked List | Solution | Easy | Linked List |
| 207. Course Schedule | Solution | Medium | Graph / BFS / Topological Sort |
| 208. Implement Trie (Prefix Tree) | Solution | Medium | Trie / Design |
| 209. Minimum Size Subarray Sum | Solution | Medium | Array / Two Pointers |
| 210. Course Schedule II | Solution | Medium | Graph / BFS / Topological Sort |
| 212. Word Search II | Solution | Hard | |
| 213. House Robber II | Solution | Medium | |
| 214. Shortest Palindrome | Solution | Medium | String |
| 215. Kth Largest Element in an Array | Solution | Medium | Medium |
| 216. Combination Sum III | Solution | Medium | |
| 217. Contains Duplicate | Solution | Easy | |
| 218. The Skyline Problem | Solution | Hard | |
| 219. Contains Duplicate II | Solution | Easy | |
| 220. Contains Duplicate III | Solution | Medium | |
| 221. Maximal Square | Solution | Medium | Dynamic Programming / BFS |
| 223. Rectangle Area | Solution | Medium | Math |
| 224. Basic Calculator | Solution | Hard | String / Stack |
| 226. Invert Binary Tree | Solution | Easy | Tree |
| 227. Basic Calculator II | Solution | Medium | String |
| 230. Kth Smallest Element in a BST | Solution | Medium | Tree |
| 231. Power of Two | Solution | Easy | Easy |
| 232. Implement Queue using Stacks | Solution | Easy | |
| 233. Number of Digit One | Solution | Hard | |
| 234. Palindrome Linked List | Solution | Easy | Linked List / Two Pointers |
| 235. Lowest Common Ancestor of a Binary Search Tree | Solution | Easy | Tree |
| 236. Lowest Common Ancestor of a Binary Tree | Solution | Medium | Tree |
| 237. Delete Node in a Linked List | Solution | Easy | |
| 238. Product of Array Except Self | Solution | Medium | Array |
| 239. Sliding Window Maximum | Solution | Hard | Heap |
| 240. Search a 2D Matrix II | Solution | Medium | Binary Search / Divide and Conquer |
| 241. Different Ways to Add Parentheses | Solution | Medium | |
| 242. Valid Anagram | Solution | Easy | |
| 243. Shortest Word Distance | Solution | Easy | |
| 246. Strobogrammatic Number | Solution | Easy | Hash Table / Math |
| 247. Strobogrammatic Number II | Solution | Medium | Math / Recursion |
| 249. Group Shifted Strings | Solution | Medium | String |
| 251. Flatten 2D Vector | Solution | Medium | Design |
| 252. Meeting Rooms | Solution | Easy | Sort |
| 253. Meeting Rooms II | Solution | Medium | Heap / Sort |
| 255. Verify Preorder Sequence in Binary Search Tree | Solution | Medium | Medium |
| 256. Paint House | Solution | Easy | |
| 257. Binary Tree Paths | Solution | Easy | Tree / DFS / BFS |
| 259. 3Sum Smaller | Solution | Medium | Array / Two Pointers |
| 261. Graph Valid Tree | Solution | Medium | Graph / BFS / DFS / Union Find |
| 263. Ugly Number | Solution | Easy | Math |
| 264. Ugly Number II | Solution | Medium | Dynamic Programming / Math |
| 265. Paint House II | Solution | Hard | |
| 267. Palindrome Permutation II | Solution | Medium | Backtracking |
| 268. Missing Number | Solution | Easy | Array / Bit Manipulation |
| 269. Alien Dictionary | Solution | Hard | Graph / Topological Sort |
| 270. Closest Binary Search Tree Value | Solution | Easy | Tree / Binary Search |
| 271. Encode and Decode Strings | Solution | Medium | String / Design |
| 272. Closest Binary Search Tree Value II | Solution | Medium | Tree / Stack |
| 273. Integer to English Words | Solution | Hard | String |
| 274. H-Index | Solution | Medium | Sort |
| 276. Paint Fence | Solution | Easy | Dynamic Programming |
| 277. Find the Celebrity | Solution | Medium | Array |
| 278. First Bad Version | Solution | Easy | Binary Search |
| 279. Perfect Squares | Solution | Medium | Math / Dynamic Programming |
| 280. Wiggle Sort | Solution | Medium | Array |
| 281. Zigzag Iterator | Solution | Medium | Design |
| 282. Expression Add Operators | Solution | Hard | Divide and Conquer |
| 283. Move Zeroes | Solution | Easy | Array / Two Pointers |
| 284. Peeking Iterator | Solution | Medium | Design |
| 285. Inorder Successor in BST | Solution | Medium | Tree |
| 286. Walls and Gates | Solution | Medium | BFS |
| 287. Find the Duplicate Number | Solution | Medium | |
| 288. Unique Word Abbreviation | Solution | Medium | |
| 289. Game of Life | Solution | Medium | Array |
| 290. Word Pattern | Solution | Easy | Hash Table |
| 291. Word Pattern II | Solution | Hard | |
| 293. Flip Game | Solution | Easy | String |
| 295. Find Median from Data Stream | Solution | Hard | Heap / Design |
| 296. Best Meeting Point | Solution | Hard | |
| 297. Serialize and Deserialize Binary Tree | Solution | Hard | Tree / Design |
| 298. Binary Tree Longest Consecutive Sequence | Solution | Medium | Tree |
| 299. Bulls and Cows | Solution | Medium | |
| 300. Longest Increasing Subsequence | Solution | Medium | Binary Search / Dynamic Programming |
| 301. Remove Invalid Parentheses | Solution | Hard | Backtracking / DFS / BFS |
| 303. Range Sum Query - Immutable | Solution | Easy | Dynamic Programming |
| 304. Range Sum Query 2D - Immutable | Solution | Medium | Dynamic Programming |
| 305. Number of Islands II | Solution | Hard | Union Find |
| 307. Range Sum Query - Mutable | Solution | Medium | Segment Tree |
| 308. Range Sum Query 2D - Mutable | Solution | Hard | |
| 309. Best Time to Buy and Sell Stock with Cooldown | Solution | Medium | Dynamic Programming |
| 310. Minimum Height Trees | Solution | Medium | BFS/ Graph |
| 311. Sparse Matrix Multiplication | Solution | Medium | Matrix |
| 312. Burst Balloons | Solution | Hard | |
| 313. Super Ugly Number | Solution | Medium | Dynamic Programming / Math |
| 314. Binary Tree Vertical Order Traversal | Solution | Medium | BFS |
| 315. Count of Smaller Numbers After Self | Solution | Hard | Divide and Conqur / Binary Search Tree |
| 317. Shortest Distance from All Buildings | Solution | Hard | BFS |
| 318. Maximum Product of Word Lengths | Solution | Medium | Bit Manipulation |
| 320. Generalized Abbreviation | Solution | Medium | |
| 322. Coin Change | Solution | Medium | |
| 323. Number of Connected Components in an Undirected Graph | Solution | Medium | Graph / Union Find / BFS / DFS |
| 324. Wiggle Sort II | Solution | Medium | |
| 325. Maximum Size Subarray Sum Equals k | Solution | Medium | Array / Hash Table |
| 327. Count of Range Sum | Solution | Hard | |
| 328. Odd Even Linked List | Solution | Medium | |
| 332. Reconstruct Itinerary | Solution | Medium | Graph / DFS |
| 333. Largest BST Subtree | Solution | Medium | Tree |
| 334. Increasing Triplet Subsequence | Solution | Medium | Array |
| 336. Palindrome Pairs | Solution | Hard | Hash Table / String / Trie |
| 337. House Robber III | Solution | Medium | |
| 338. Counting Bits | Solution | Medium | |
| 339. Nested List Weight Sum | Solution | Easy | DFS |
| 340. Longest Substring with At Most K Distinct Characters | Solution | Hard | Hash Table / String |
| 343. Integer Break | Solution | Medium | |
| 344. Reverse String | Solution | Easy | String |
| 345. Reverse Vowels of a String | Solution | Easy | |
| 346. Moving Average from Data Stream | Solution | Easy | |
| 347. Top K Frequent Elements | Solution | Medium | Hash Table / Heap |
| 348. Design Tic-Tac-Toe | Solution | Medium | Design |
| 349. Intersection of Two Arrays | Solution | Easy | |
| 350. Intersection of Two Arrays II | Solution | Easy | |
| 351. Android Unlock Patterns | Solution | Medium | DFS / Dynamic Programming |
| 352. Data Stream as Disjoint Intervals | Solution | Hard | |
| 353. Design Snake Game | Solution | Medium | |
| 354. Russian Doll Envelopes | Solution | Hard | Binary Search / Dynamic Programming |
| 355. Design Twitter | Solution | Medium | Hash Table / Design |
| 357. Count Numbers with Unique Digits | Solution | Medium | |
| 358. Rearrange String k Distance Apart | Solution | Hard | |
| 359. Logger Rate Limiter | Solution | Easy | Hash Table / Design |
| 360. Sort Transformed Array | Solution | Medium | Math / Two Pointers |
| 361. Bomb Enemy | Solution | Medium | Dynamic Programming |
| 362. Design Hit Counter | Solution | Medium | Design |
| 363. Max Sum of Rectangle No Larger Than K | Solution | Hard | |
| 365. Water and Jug Problem | Solution | Medium | |
| 368. Largest Divisible Subset | Solution | Medium | |
| 369. Plus One Linked List | Solution | Medium | Linked List |
| 370. Range Addition | Solution | Medium | |
| 373. Find K Pairs with Smallest Sums | Solution | Medium | Heap |
| 375. Guess Number Higher or Lower II | Solution | Medium | |
| 377. Combination Sum IV | Solution | Medium | Dynamic Programming |
| 378. Kth Smallest Element in a Sorted Matrix | Solution | Medium | Binary Search / Heap |
| 380. Insert Delete GetRandom O(1) | Solution | Medium | Hash Table / Design |
| 382. Linked List Random Node | Solution | Medium | Reservoir Sampling |
| 383. Ransom Note | Solution | Easy | |
| 384. Shuffle an Array | Solution | Medium | |
| 386. Lexicographical Numbers | Solution | Medium | |
| 387. First Unique Character in a String | Solution | Easy | |
| 392. Is Subsequence | Solution | Medium | |
| 393. UTF-8 Validation | Solution | Medium | |
| 394. Decode String | Solution | Medium | String / DFS |
| 396. Rotate Function | Solution | Medium | |
| 399. Evaluate Division | Solution | Medium | Graph |
| 403. Frog Jump | Solution | Hard | |
| 405. Convert a Number to Hexadecimal | Solution | Easy | |
| 406. Queue Reconstruction by Height | Solution | Medium | |
| 407. Trapping Rain Water II | Solution | Medium | |
| 408. Valid Word Abbreviation | Solution | Easy | String |
| 409. Longest Palindrome | Solution | Easy | Hash Table |
| 410. Split Array Largest Sum | Solution | Hard | |
| 412. Fizz Buzz | Solution | Easy | Array |
| 416. Partition Equal Subset Sum | Solution | Medium | Dynamic Programming |
| 417. Pacific Atlantic Water Flow | Solution | Medium | DFS / BFS |
| 418. Sentence Screen Fitting | Solution | Medium | Dynamic Programming |
| 433. Minimum Genetic Mutation | Solution | Medium | BFS |
| 435. Non-overlapping Intervals | Solution | Medium | Greedy |
| 436. Find Right Interval | Solution | Medium | Array / Binary Search |
| 438. Find All Anagrams in a String | Solution | Easy | Hash Table |
| 441. Arranging Coins | Solution | Easy | Math |
| 444. Sequence Reconstruction | Solution | Medium | Graph / Topological Sort |
| 450. Delete Node in a BST | Solution | Medium | Tree |
| 451. Sort Characters By Frequency | Solution | Medium | Hash Table / Heap |
| 461. Hamming Distance | Solution | Easy | Bit Manipulation |
| 467. Unique Substrings in Wraparound String | Solution | Medium | Dynamic Programming |
| 473. Matchsticks to Square | Solution | Medium | DFS |
| 477. Total Hamming Distance | Solution | Medium | Bit Manipulation |
| 482. License Key Formatting | Solution | Medium | Array |
| 484. Find Permutation | Solution | Medium | Greedy |
| 486. Predict the Winner | Solution | Medium | Dynamic Programming / Minimax |
| 487. Max Consecutive Ones II | Solution | Medium | Two Pointers |
| 489. Robot Room Cleaner | Solution | Hard | DFS |
| 490. The Maze | Solution | Medium | BFS / DFS |
| 494. Target Sum | Solution | Medium | Backtracking |
| 496. Next Greater Element I | Solution | Easy | Stack |
| 498. Diagonal Traverse | Solution | Medium | Matrix |
| 499. The Maze III | Solution | Hard | DFS / BFS |