| 98. Validate Binary Search Tree | Medium | TreeDepth-First SearchBinary Search Tree+1 more |
| 100. Same Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 102. Binary Tree Level Order Traversal | Medium | TreeBreadth-First SearchBinary Tree |
| 103. Binary Tree Zigzag Level Order Traversal | Medium | TreeBreadth-First SearchBinary Tree |
| 104. Maximum Depth of Binary Tree | Easy | TreeDepth-First SearchBreadth-First Search+1 more |
| 105. Construct Binary Tree from Preorder and Inorder Traversal | Medium | ArrayHash TableDivide and Conquer+2 more |
| 106. Construct Binary Tree from Inorder and Postorder Traversal | Medium | ArrayHash TableDivide and Conquer+2 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 |
| 199. Binary Tree Right Side View | Medium | TreeDepth-First SearchBreadth-First Search+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 |