| 1. Two Sum | Easy | ArrayHash Table |
| 15. 3Sum | Medium | ArrayTwo PointersSorting |
| 19. Remove Nth Node From End of List | Medium | Linked ListTwo Pointers |
| 21. Merge Two Sorted Lists | Easy | Linked ListRecursion |
| 31. Next Permutation | Medium | ArrayTwo Pointers |
| 33. Search in Rotated Sorted Array | Medium | ArrayBinary Search |
| 42. Trapping Rain Water | Hard | ArrayTwo PointersDynamic Programming+2 more |
| 48. Rotate Image | Medium | ArrayMathMatrix |
| 53. Maximum Subarray | Medium | ArrayDivide and ConquerDynamic Programming |
| 54. Spiral Matrix | Medium | ArrayMatrixSimulation |
| 56. Merge Intervals | Medium | ArraySorting |
| 57. Insert Interval | Medium | Array |
| 62. Unique Paths | Medium | MathDynamic ProgrammingCombinatorics |
| 70. Climbing Stairs | Easy | MathDynamic ProgrammingMemoization |
| 73. Set Matrix Zeroes | Medium | ArrayHash TableMatrix |
| 74. Search a 2D Matrix | Medium | ArrayBinary SearchMatrix |
| 79. Word Search | Medium | ArrayStringBacktracking+2 more |
| 91. Decode Ways | Medium | StringDynamic Programming |
| 98. Validate Binary Search Tree | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 102. Binary Tree Level Order Traversal | Medium | TreeBreadth-First SearchBinary Tree |
| 104. Maximum Depth of Binary Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 110. Balanced Binary Tree | Easy | TreeDepth-First SearchBinary Tree |
| 118. Pascal's Triangle | Easy | ArrayDynamic Programming |
| 121. Best Time to Buy and Sell Stock | Easy | ArrayDynamic Programming |
| 128. Longest Consecutive Sequence | Medium | ArrayHash TableUnion-Find |
| 133. Clone Graph | Medium | Hash TableDepth-First SearchBreadth-First Search+1 more |
| 139. Word Break | Medium | ArrayHash TableString+3 more |
| 141. Linked List Cycle | Easy | Hash TableLinked ListTwo Pointers |
| 152. Maximum Product Subarray | Medium | ArrayDynamic Programming |
| 153. Find Minimum in Rotated Sorted Array | Medium | ArrayBinary Search |
| 169. Majority Element | Easy | ArrayHash TableDivide and Conquer+2 more |
| 198. House Robber | Medium | ArrayDynamic Programming |
| 199. Binary Tree Right Side View | Medium | TreeDepth-First SearchBreadth-First Search+1 more |
| 200. Number of Islands | Medium | ArrayDepth-First SearchBreadth-First Search+2 more |
| 206. Reverse Linked List | Easy | Linked ListRecursion |
| 207. Course Schedule | Medium | Depth-First SearchBreadth-First SearchGraph Theory+1 more |
| 215. Kth Largest Element in an Array | Medium | ArrayDivide and ConquerSorting+2 more |
| 217. Contains Duplicate | Easy | ArrayHash TableSorting |
| 230. Kth Smallest Element in a BST | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 238. Product of Array Except Self | Medium | ArrayPrefix Sum |