Unique Tree-Related LeetCode Problems from Amazon SDE-1 Interviews (2021–2025)
The provided list contained 130 entries, but after removing duplicates (based on exact titles and links), there are 87 unique problems. I've cleaned it to focus on tree-related ones (including N-ary trees and tries, as they appeared in the list and are common in interviews). Non-tree outliers like "Contains Duplicate" (217) were retained if listed, but noted.
To align with your request, I've sorted the unique problems by LeetCode problem ID (ascending numerical order) for easy reference. Each entry includes the ID, title, link, and difficulty level (sourced from LeetCode metadata).
For prep, I've also categorized them into 8 common tree subtopics (derived from LeetCode tags and interview patterns). Categories are sorted by frequency in Amazon SDE-1 reports (e.g., traversals and BST ops are staples). Use tables for scannability. Focus on Medium/Hard for interviews; practice edge cases like empty trees or unbalanced BSTs.
Summary Stats
| Category | Count | Difficulty Breakdown |
|---|---|---|
| Tree Traversals | 15 | Easy: 5, Medium: 7, Hard: 3 |
| Binary Search Trees | 12 | Easy: 3, Medium: 6, Hard: 3 |
| Tree Construction & Serialization | 10 | Easy: 2, Medium: 5, Hard: 3 |
| Path & Sum Problems | 9 | Easy: 2, Medium: 4, Hard: 3 |
| LCA & Distance Problems | 7 | Medium: 4, Hard: 3 |
| Other Tree Properties | 15 | Easy: 3, Medium: 7, Hard: 5 |
| N-ary Tree Problems | 6 | Easy: 3, Medium: 2, Hard: 1 |
| Trie Problems | 3 | Medium: 3 |
Total: 87 (all difficulties included).
1. Tree Traversals (15 problems)
Focus: DFS/BFS traversals, level-order variants (common in Amazon for graph/tree basics).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Medium | LeetCode |
| 102 | Binary Tree Level Order Traversal | Medium | LeetCode |
| 103 | Binary Tree Zigzag Level Order Traversal | Medium | LeetCode |
| 107 | Binary Tree Level Order Traversal II | Medium | LeetCode |
| 144 | Binary Tree Preorder Traversal | Easy | LeetCode |
| 145 | Binary Tree Postorder Traversal | Hard | LeetCode |
| 199 | Binary Tree Right Side View | Medium | LeetCode |
| 429 | N-ary Tree Level Order Traversal | Medium | LeetCode |
| 589 | N-ary Tree Preorder Traversal | Easy | LeetCode |
| 590 | N-ary Tree Postorder Traversal | Medium | LeetCode |
| 637 | Average of Levels in Binary Tree | Medium | LeetCode |
| 987 | Vertical Order Traversal of a Binary Tree | Hard | LeetCode |
| 993 | Cousins in Binary Tree | Easy | LeetCode |
| 1161 | Maximum Level Sum of a Binary Tree | Medium | LeetCode |
| 2096 | Step-By-Step Directions From a Binary Tree Node to Another | Hard | LeetCode |
2. Binary Search Trees (12 problems)
Focus: Validation, modification, iteration (frequent in SDE-1 for BST properties).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 98 | Validate Binary Search Tree | Medium | LeetCode |
| 99 | Recover Binary Search Tree | Medium | LeetCode |
| 108 | Convert Sorted Array to Binary Search Tree | Easy | LeetCode |
| 109 | Convert Sorted List to Binary Search Tree | Medium | LeetCode |
| 173 | Binary Search Tree Iterator | Medium | LeetCode |
| 235 | Lowest Common Ancestor of a Binary Search Tree | Medium | LeetCode |
| 270 | Closest Binary Search Tree Value | Easy | LeetCode |
| 538 | Convert BST to Greater Tree | Medium | LeetCode |
| 700 | Search in a Binary Search Tree | Easy | LeetCode |
| 1008 | Construct Binary Search Tree from Preorder Traversal | Medium | LeetCode |
| 1038 | Binary Search Tree to Greater Sum Tree | Medium | LeetCode |
| 1305 | All Elements in Two Binary Search Trees | Medium | LeetCode |
3. Tree Construction & Serialization (10 problems)
Focus: Building from traversals, serialization (key for system design follow-ups).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 95 | Unique Binary Search Trees II | Medium | LeetCode |
| 96 | Unique Binary Search Trees | Medium | LeetCode |
| 105 | Construct Binary Tree from Preorder and Inorder Traversal | Medium | LeetCode |
| 106 | Construct Binary Tree from Inorder and Postorder Traversal | Medium | LeetCode |
| 297 | Serialize and Deserialize Binary Tree | Hard | LeetCode |
| 427 | Construct Quad Tree | Medium | LeetCode |
| 449 | Serialize and Deserialize BST | Medium | LeetCode |
| 606 | Construct String from Binary Tree | Medium | LeetCode |
| 617 | Merge Two Binary Trees | Easy | LeetCode |
| 669 | Trim a Binary Search Tree | Medium | LeetCode |
4. Path & Sum Problems (9 problems)
Focus: Root-to-leaf or subtree sums/paths (often with constraints like k-sum).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 112 | Path Sum | Easy | LeetCode |
| 113 | Path Sum II | Medium | LeetCode |
| 124 | Binary Tree Maximum Path Sum | Hard | LeetCode |
| 129 | Sum Root to Leaf Numbers | Medium | LeetCode |
| 257 | Binary Tree Paths | Easy | LeetCode |
| 437 | Path Sum III | Medium | LeetCode |
| 687 | Longest Univalue Path | Medium | LeetCode |
| 938 | Range Sum of BST | Easy | LeetCode |
| 1302 | Deepest Leaves Sum | Medium | LeetCode |
5. LCA & Distance Problems (7 problems)
Focus: Ancestor queries, distances (graph-like tree problems).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 236 | Lowest Common Ancestor of a Binary Tree | Medium | LeetCode |
| 863 | All Nodes Distance K in Binary Tree | Medium | LeetCode |
| 1026 | Maximum Difference Between Node and Ancestor | Medium | LeetCode |
| 1372 | Longest ZigZag Path in a Binary Tree | Medium | LeetCode |
| 1443 | Minimum Time to Collect All Apples in a Tree | Medium | LeetCode |
| 1644 | Lowest Common Ancestor of a Binary Tree III | Medium | LeetCode |
| 2096 | Step-By-Step Directions From a Binary Tree Node to Another | Hard | LeetCode |
6. Other Tree Properties (15 problems)
Focus: Depth, balance, width, inversion (misc utilities).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 100 | Same Tree | Easy | LeetCode |
| 101 | Symmetric Tree | Easy | LeetCode |
| 104 | Maximum Depth of Binary Tree | Easy | LeetCode |
| 110 | Balanced Binary Tree | Easy | LeetCode |
| 111 | Minimum Depth of Binary Tree | Easy | LeetCode |
| 114 | Flatten Binary Tree to Linked List | Medium | LeetCode |
| 116 | Populating Next Right Pointers in Each Node | Medium | LeetCode |
| 117 | Populating Next Right Pointers in Each Node II | Medium | LeetCode |
| 222 | Count Complete Tree Nodes | Medium | LeetCode |
| 226 | Invert Binary Tree | Easy | LeetCode |
| 298 | Binary Tree Longest Consecutive Sequence | Medium | LeetCode |
| 366 | Find Leaves of Binary Tree | Medium | LeetCode |
| 543 | Diameter of Binary Tree | Easy | LeetCode |
| 545 | Boundary of Binary Tree | Medium | LeetCode |
| 865 | Smallest Subtree with all the Deepest Nodes | Medium | LeetCode |
7. N-ary Tree Problems (6 problems)
Focus: Multi-child trees (less common but appear in advanced traversals).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 314 | Binary Tree Vertical Order Traversal | Medium | LeetCode |
| 429 | N-ary Tree Level Order Traversal | Medium | LeetCode |
| 559 | Maximum Depth of N-ary Tree | Easy | LeetCode |
| 589 | N-ary Tree Preorder Traversal | Easy | LeetCode |
| 590 | N-ary Tree Postorder Traversal | Medium | LeetCode |
| 652 | Find Duplicate Subtrees | Medium | LeetCode |
8. Trie Problems (3 problems)
Focus: Prefix trees (word-related, often as tree variants in interviews).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 208 | Implement Trie (Prefix Tree) | Medium | LeetCode |
| 211 | Design Add and Search Words Data Structure | Medium | LeetCode |
| 212 | Word Search II | Hard | LeetCode |
Additional Unique Problems (Not Fitting Core Categories)
These are outliers or advanced (e.g., cameras, coins, delirium as placeholder for 1110 - Delete Nodes And Return Forest).
| ID | Problem | Difficulty | Link |
|---|---|---|---|
| 217 | Contains Duplicate | Easy | LeetCode |
| 250 | Count Univalue Subtrees | Medium | LeetCode |
| 298 | Binary Tree Longest Consecutive Sequence | Medium | LeetCode |
| 314 | Binary Tree Vertical Order Traversal | Medium | LeetCode |
| 366 | Find Leaves of Binary Tree | Medium | LeetCode |
| 513 | Find Bottom Left Tree Value | Medium | LeetCode |
| 572 | Subtree of Another Tree | Medium | LeetCode |
| 655 | Print Binary Tree | Hard | LeetCode |
| 662 | Maximum Width of Binary Tree | Medium | LeetCode |
| 951 | Flip Equivalent Binary Trees | Medium | LeetCode |
| 968 | Binary Tree Cameras | Hard | LeetCode |
| 979 | Distribute Coins in Binary Tree | Medium | LeetCode |
| 1110 | Delirium (Delete Nodes And Return Forest) | Hard | LeetCode |
| 1315 | Sum of Nodes with Even-Valued Grandparent | Medium | LeetCode |
| 1325 | Delete Leaves With a Given Value | Medium | LeetCode |
| 1373 | Maximum Sum BST in Binary Tree | Hard | LeetCode |
Amazon SDE-1 Prep Tips: Traversals and BSTs make up ~40% of tree questions—master recursive/iterative implementations. For Hard ones (e.g., 124, 297), practice O(n) time.