Array

• 26. Remove Duplicates from Sorted Array
• 27. Remove Element
• 31. Next Permutation
• 41. First Missing Positive
• 54. Spiral Matrix
• 56. Merge Intervals
• 57. Insert Interval
• 59. Spiral Matrix II
• 73. Set Matrix Zeroes
• 118. Pascal's Triangle
• 119. Pascal's Triangle II
• 164. Maximum Gap
• 189. Rotate Array
• 228. Summary Ranges
• 289. Game of Life

String

• 6. ZigZag Conversion
• 8. String to Integer
• 14. Longest Common Prefix
• 17. Letter Combinations of a Phone Number
• 28. Implement strStr()
• 58. Length of Last Word
• 67. Add Binary
• 68. Text Justification
• 151. Reverse Words in a String
• 165. Compare Version Numbers
• 344. Reverse String

Linked List

• 2. Add Two Numbers
• 21. Merge Two Sorted Lists
• 24. Swap Nodes in Pairs
• 25. Reverse Nodes in k-Group
• 61. Rotate List
• 76. Minimum Window Substring
• 82. Remove Duplicates from Sorted List II
• 83. Remove Duplicates from Sorted List
• 86. Partition List
• 92. Reverse Linked List II
• 138. Copy List with Random Pointer
• 143. Reorder List
• 147. Insertion Sort List
• 148. Sort List
• 160. Intersection of Two Linked Lists
• 203. Remove Linked List Elements
• 206. Reverse Linked List
• 234. Palindrome Linked List
• 237. Delete Node in a Linked List
• 328. Odd Even Linked List

Tree

• 94. Binary Tree Inorder Traversa
• 95. Unique Binary Search Trees II
• 96. Unique Binary Search Trees
• 99. Recover Binary Search Tree
• 100. Same Tree
• 105. Construct Binary Tree from Preorder and Inorder Traversal
• 106. Construct Binary Tree from Inorder and Postorder Traversal
• 108. Convert Sorted Array to Binary Search Tree
• 109. Convert Sorted List to Binary Search Tree
• 110. Balanced Binary Tree
• 111. Minimum Depth of Binary Tree
• 112. Path Sum
• 113. Path Sum II
• 114. Flatten Binary Tree to Linked List
• 116. Populating Next Right Pointers in Each Node
• 117. Populating Next Right Pointers in Each Node II
• 124. Binary Tree Maximum Path Sum
• 144. Binary Tree Preorder Traversal
• 145. Binary Tree Postorder Traversal
• 173. Binary Search Tree Iterator
• 208. Implement Trie (Prefix Tree)
• 211. Add and Search Word
• 226. Invert Binary Tree
• 235. Lowest Common Ancestor of a Binary Search Tree
• 236. Lowest Common Ancestor of a Binary Tree
• 297. Serialize and Deserialize Binary Tree
• 331. Verify Preorder Serialization of a Binary Tree

Hash Table

• 1. Two Sum
• 3. Longest Substring Without Repeating Characters
• 18. 4Sum
• 49. Group Anagrams
• 128. Longest Consecutive Sequence
• 146. LRU Cache
• 149. Max Points on a Line
• 187. Repeated DNA Sequences
• 205. Isomorphic Strings
• 217. Contains Duplicate
• 219. Contains Duplicate II
• 242. Valid Anagram
• 257. Binary Tree Paths
• 274. H-Index
• 290. Word Pattern
• 299. Bulls and Cows
• 349. Intersection of Two Arrays
• 350. Intersection of Two Arrays II

Heap

• 23. Merge k Sorted Lists
• 295. Find Median from Data Stream
• 347. Top K Frequent Elements

Binary Search

• 4. Median of Two Sorted Arrays
• 33. Search in Rotated Sorted Array
• 34. Search for a Range
• 69. Sqrt(x)
• 74. Search a 2D Matrix
• 81. Search in Rotated Sorted Array II
• 153. Find Minimum in Rotated Sorted Array
• 154. Find Minimum in Rotated Sorted Array II
• 162. Find Peak Element
• 222. Count Complete Tree Nodes
• 230. Kth Smallest Element in a BST
• 275. H-Index II
• 278. First Bad Version
• 367. Valid Perfect Square

Depth-first Search

• 98. Validate Binary Search Tree
• 126. Word Ladder II
• 129. Sum Root to Leaf Numbers
• 140. Word Break II
• 200. Number of Islands
• 301. Remove Invalid Parentheses
• 306. Additive Number

Breadth-first Search

• 102. Binary Tree Level Order Traversal
• 103. Binary Tree Zigzag Level OrderTraversal
• 104. Maximum Depth Of BinaryTree
• 107. Binary Tree Level Order Traversal II
• 126. Word Ladder II
• 127. Word Ladder
• 130. Surrounded Regions
• 199. Binary Tree Right Side View
• 310. Minimum Height Trees
• 322. Coin Change

Backtracking

• 22. Generate Parentheses
• 46. Permutations
• 47. Permutations II
• 51. N-Queens
• 52. N-Queens II
• 79. Word Search
• 90. Subsets II
• 93. Restore IP Addresses
• 131. Palindrome Partitioning
• 216. Combination Sum III

Recursion

• 60. Permutation Sequence
• 77. Combinations
• 89. Gray Code
• 101. Symmetric Tree

Dynamic Programming

• 10. Regular Expression Matching
• 32. Longest Valid Parentheses
• 53. Maximum Subarray
• 62. Unique Paths
• 63. Unique Paths II
• 64. Minimum Path Sum
• 70. Climbing Stairs
• 72. Edit Distance
• 87. Scramble String
• 91. Decode Ways
• 97. Interleaving String
• 115. Distinct Subsequences
• 120. Triangle
• 121. Best Time to Buy and Sell Stock
• 123. Best Time to Buy and Sell Stock III
• 132. Palindrome Partitioning II
• 135. Candy
• 139. Word Break
• 152. Maximum Product Subarray
• 174. Dungeon Game
• 188. Best Time to Buy and Sell Stock IV
• 198. House Robber
• 213. House Robber II
• 221. Maximal Square
• 264. Ugly Number II
• 279. Perfect Squares
• 303. Range Sum Query - Immutable
• 304. Range Sum Query 2D - Immutable
• 309. Best Time to Buy and Sell Stock with Cooldown
• 313. Super Ugly Number
• 337. House Robber III
• 368. Largest Divisible Subset
• 357. Count Numbers with Unique Digits

Greedy

• 55. Jump Game
• 122. Best Time to Buy and Sell Stock II
• 134. Gas Station
• 316. Remove Duplicate Letters
• 330. Patching Array

Stack

• 20. Valid Parentheses
• 32. Longest Valid Parentheses
• 71. Simplify Path
• 84. Largest Rectangle in Histogram
• 85. Maximal Rectangle
• 94. Binary Tree Inorder Traversal
• 150. Evaluate Reverse Polish Notation
• 155. Min Stack
• 224. Basic Calculator
• 225. Implement Stack using Queues
• 227. Basic Calculator II
• 232. Implement Queue using Stacks
• 316. Remove Duplicate Letters
• 341. Flatten Nested List Iterator

Two Pointers

• 11. Container With Most Water
• 15. 3Sum
• 16. 3Sum Closest
• 18. 4Sum
• 19. Remove Nth Node From End of List
• 75. Sort Colors
• 80. Remove Duplicates from Sorted Array II
• 88. Merge Sorted Array
• 125. Valid Palindrome
• 141. Linked List Cycle
• 142. Linked List Cycle II
• 209. Minimum Size Subarray Sum
• 283. Move Zeroes
• 287. Find the Duplicate Number
• 345. Reverse Vowels of a String

Math

• 7. Reverse Integer
• 9. Palindrome Number
• 12. Integer to Roman
• 13. Roman to Integer
• 48. Rotate Image
• 50. Pow(x, n)
• 60. Permutation Sequence
• 66. Plus One
• 69. Sqrt(x)
• 166. Fraction to Recurring Decimal
• 168. Excel Sheet Column Title
• 171. Excel Sheet Column Number
• 172. Factorial Trailing Zeroes
• 179. Largest Number
• 202. Happy Number
• 204. Count Primes
• 223. Rectangle Area
• 233. Number of Digit One
• 238. Product of Array Except Self
• 258. Add Digits
• 263. Ugly Number
• 273. Integer to English Words
• 292. Nim Game
• 326. Power of Three
• 319. Bulb Switcher
• 335. Self Crossing
• 343. Integer Break

Bit Manipulation

• 29. Divide Two Integers
• 78. Subsets
• 136. Single Number
• 137. Single Number II
• 169. Majority Element
• 190. Reverse Bits
• 191. Number of 1 Bits
• 201. Bitwise AND of Numbers Range
• 231. Power of Two
• 260. Single Number III
• 268. Missing Number
• 318. Maximum Product of Word Lengths
• 338. Counting Bits
• 371. Sum of Two Integers
• 342. Power of Four

Graph

• 133. Clone Graph
• 207. Course Schedule
• 210. Course Schedule II

Combination

• 30. Substring with Concatenation of All Words
• 140. Word Break II
• 146. LRU Cache
• 300. Longest Increasing Subsequence
• 329. Longest Increasing Path in a Matrix
• 355. Design Twitter

DFA

• 65. Valid Number

Divide and Conquer

• 215. Kth Largest Element in an Array
• 240. Search a 2D Matrix II
• 241. Different Ways to Add Parentheses

Others

• 220. Contains Duplicate III
• 229. Majority Element II
• 239. Sliding Window Maximum
• 284. Peeking Iterator
• 307. Range Sum Query - Mutable