| 79. Word Search | Medium | ArrayStringBacktracking+2 more |
| 98. Validate Binary Search Tree | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 100. Same Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 104. Maximum Depth of Binary Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 110. Balanced Binary Tree | Easy | TreeDepth-First SearchBinary Tree |
| 112. Path Sum | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 113. Path Sum II | Medium | BacktrackingTreeDepth-First Search+1 more |
| 114. Flatten Binary Tree to Linked List | Medium | Linked ListStackTree+2 more |
| 124. Binary Tree Maximum Path Sum | Hard | Dynamic ProgrammingTreeDepth-First Search+1 more |
| 130. Surrounded Regions | Medium | ArrayDepth-First SearchBreadth-First Search+2 more |
| 133. Clone Graph | Medium | Hash TableDepth-First SearchBreadth-First Search+1 more |
| 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 |
| 207. Course Schedule | Medium | Depth-First SearchBreadth-First SearchGraph Theory+1 more |
| 210. Course Schedule II | Medium | Depth-First SearchBreadth-First SearchGraph Theory+1 more |
| 211. Design Add and Search Words Data Structure | Medium | StringDepth-First SearchDesign+1 more |
| 226. Invert Binary Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 230. Kth Smallest Element in a BST | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 235. Lowest Common Ancestor of a Binary Search Tree | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 236. Lowest Common Ancestor of a Binary Tree | Medium | TreeDepth-First SearchBinary Tree |