Binary Tree LeetCode Problems: All 174, With Python Solutions
Every problem in this library that LeetCode tags Binary Tree — 174 in total, 128 of them with a complete Python solution, a worked example and the time and space complexity of the approach.
- 174 problems
- 38 Easy
- 120 Medium
- 16 Hard
How Binary Tree problems are solved
A tag names the subject, not the method. These pattern hubs cover the techniques that actually solve Binary Tree problems — each one explains the approach, gives a Python template and states its complexity.
- Tree Traversal — Choose the order — preorder, inorder, postorder, level — and the problem solves itself.
Binary Tree problems by difficulty
Problems with a complete Python solution are listed first, then by ascending problem number.
Easy (38)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 94 | Binary Tree Inorder Traversal | Easy | Stack, Tree, Depth-First Search +1 |
| 100 | Same Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 101 | Symmetric Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 104 | Maximum Depth of Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 108 | Convert Sorted Array to Binary Search Tree | Easy | Tree, Binary Search Tree, Array +2 |
| 110 | Balanced Binary Tree | Easy | Tree, Depth-First Search, Binary Tree |
| 111 | Minimum Depth of Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 112 | Path Sum | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 144 | Binary Tree Preorder Traversal | Easy | Stack, Tree, Depth-First Search +1 |
| 145 | Binary Tree Postorder Traversal | Easy | Stack, Tree, Depth-First Search +1 |
| 222 | Count Complete Tree Nodes | Easy | Bit Manipulation, Tree, Binary Search +1 |
| 226 | Invert Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 257 | Binary Tree Paths | Easy | Tree, Depth-First Search, String +2 |
| 404 | Sum of Left Leaves | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 501 | Find Mode in Binary Search Tree | Easy | Tree, Depth-First Search, Binary Search Tree +1 |
| 530 | Minimum Absolute Difference in BST | Easy | Tree, Depth-First Search, Breadth-First Search +2 |
| 543 | Diameter of Binary Tree | Easy | Tree, Depth-First Search, Binary Tree |
| 563 | Binary Tree Tilt | Easy | Tree, Depth-First Search, Binary Tree |
| 572 | Subtree of Another Tree | Easy | Tree, Depth-First Search, Binary Tree +2 |
| 617 | Merge Two Binary Trees | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 637 | Average of Levels in Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 653 | Two Sum IV - Input is a BST | Easy | Tree, Depth-First Search, Breadth-First Search +4 |
| 671 | Second Minimum Node In a Binary Tree | Easy | Tree, Depth-First Search, Binary Tree |
| 700 | Search in a Binary Search Tree | Easy | Tree, Binary Search Tree, Binary Tree |
| 703 | Kth Largest Element in a Stream | Easy | Tree, Design, Binary Search Tree +3 |
| 783 | Minimum Distance Between BST Nodes | Easy | Tree, Depth-First Search, Breadth-First Search +2 |
| 872 | Leaf-Similar Trees | Easy | Tree, Depth-First Search, Binary Tree |
| 897 | Increasing Order Search Tree | Easy | Stack, Tree, Depth-First Search +2 |
| 938 | Range Sum of BST | Easy | Tree, Depth-First Search, Binary Search Tree +1 |
| 965 | Univalued Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 993 | Cousins in Binary Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 1022 | Sum of Root To Leaf Binary Numbers | Easy | Tree, Depth-First Search, Binary Tree |
| 1379 | Find a Corresponding Node of a Binary Tree in a Clone of That Tree | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 2236 | Root Equals Sum of Children | Easy | Tree, Binary Tree |
| 2331 | Evaluate Boolean Binary Tree | Easy | Tree, Depth-First Search, Binary Tree |
| 270 | Closest Binary Search Tree ValuePremium | Easy | Tree, Depth-First Search, Binary Search Tree +2 |
| 1469 | Find All The Lonely NodesPremium | Easy | Tree, Depth-First Search, Breadth-First Search +1 |
| 2689 | Extract Kth Character From The Rope TreePremium | Easy | Tree, Depth-First Search, Binary Tree |
Medium (120)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 95 | Unique Binary Search Trees II | Medium | Tree, Binary Search Tree, Dynamic Programming +2 |
| 96 | Unique Binary Search Trees | Medium | Tree, Binary Search Tree, Math +2 |
| 98 | Validate Binary Search Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 99 | Recover Binary Search Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 102 | Binary Tree Level Order Traversal | Medium | Tree, Breadth-First Search, Binary Tree |
| 103 | Binary Tree Zigzag Level Order Traversal | Medium | Tree, Breadth-First Search, Binary Tree |
| 105 | Construct Binary Tree from Preorder and Inorder Traversal | Medium | Tree, Array, Hash Table +2 |
| 106 | Construct Binary Tree from Inorder and Postorder Traversal | Medium | Tree, Array, Hash Table +2 |
| 107 | Binary Tree Level Order Traversal II | Medium | Tree, Breadth-First Search, Binary Tree |
| 109 | Convert Sorted List to Binary Search Tree | Medium | Tree, Binary Search Tree, Linked List +2 |
| 113 | Path Sum II | Medium | Tree, Depth-First Search, Backtracking +1 |
| 114 | Flatten Binary Tree to Linked List | Medium | Stack, Tree, Depth-First Search +2 |
| 116 | Populating Next Right Pointers in Each Node | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 117 | Populating Next Right Pointers in Each Node II | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 129 | Sum Root to Leaf Numbers | Medium | Tree, Depth-First Search, Binary Tree |
| 173 | Binary Search Tree Iterator | Medium | Stack, Tree, Design +3 |
| 199 | Binary Tree Right Side View | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 230 | Kth Smallest Element in a BST | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 235 | Lowest Common Ancestor of a Binary Search Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 236 | Lowest Common Ancestor of a Binary Tree | Medium | Tree, Depth-First Search, Binary Tree |
| 331 | Verify Preorder Serialization of a Binary Tree | Medium | Stack, Tree, String +1 |
| 337 | House Robber III | Medium | Tree, Depth-First Search, Dynamic Programming +1 |
| 437 | Path Sum III | Medium | Tree, Depth-First Search, Binary Tree |
| 449 | Serialize and Deserialize BST | Medium | Tree, Depth-First Search, Breadth-First Search +4 |
| 450 | Delete Node in a BST | Medium | Tree, Binary Search Tree, Binary Tree |
| 508 | Most Frequent Subtree Sum | Medium | Tree, Depth-First Search, Hash Table +1 |
| 513 | Find Bottom Left Tree Value | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 515 | Find Largest Value in Each Tree Row | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 538 | Convert BST to Greater Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 606 | Construct String from Binary Tree | Medium | Tree, Depth-First Search, String +1 |
| 623 | Add One Row to Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 652 | Find Duplicate Subtrees | Medium | Tree, Depth-First Search, Hash Table +1 |
| 654 | Maximum Binary Tree | Medium | Stack, Tree, Array +3 |
| 655 | Print Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 662 | Maximum Width of Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 669 | Trim a Binary Search Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 687 | Longest Univalue Path | Medium | Tree, Depth-First Search, Binary Tree |
| 701 | Insert into a Binary Search Tree | Medium | Tree, Binary Search Tree, Binary Tree |
| 814 | Binary Tree Pruning | Medium | Tree, Depth-First Search, Binary Tree |
| 863 | All Nodes Distance K in Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 865 | Smallest Subtree with all the Deepest Nodes | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 889 | Construct Binary Tree from Preorder and Postorder Traversal | Medium | Tree, Array, Hash Table +2 |
| 894 | All Possible Full Binary Trees | Medium | Tree, Recursion, Memoization +2 |
| 919 | Complete Binary Tree Inserter | Medium | Tree, Breadth-First Search, Design +1 |
| 951 | Flip Equivalent Binary Trees | Medium | Tree, Depth-First Search, Binary Tree |
| 958 | Check Completeness of a Binary Tree | Medium | Tree, Breadth-First Search, Binary Tree |
| 971 | Flip Binary Tree To Match Preorder Traversal | Medium | Tree, Depth-First Search, Binary Tree |
| 979 | Distribute Coins in Binary Tree | Medium | Tree, Depth-First Search, Binary Tree |
| 988 | Smallest String Starting From Leaf | Medium | Tree, Depth-First Search, String +2 |
| 998 | Maximum Binary Tree II | Medium | Tree, Binary Tree |
| 1008 | Construct Binary Search Tree from Preorder Traversal | Medium | Stack, Tree, Binary Search Tree +3 |
| 1026 | Maximum Difference Between Node and Ancestor | Medium | Tree, Depth-First Search, Binary Tree |
| 1038 | Binary Search Tree to Greater Sum Tree | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 1080 | Insufficient Nodes in Root to Leaf Paths | Medium | Tree, Depth-First Search, Binary Tree |
| 1104 | Path In Zigzag Labelled Binary Tree | Medium | Tree, Math, Binary Tree |
| 1110 | Delete Nodes And Return Forest | Medium | Tree, Depth-First Search, Array +2 |
| 1123 | Lowest Common Ancestor of Deepest Leaves | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1145 | Binary Tree Coloring Game | Medium | Tree, Depth-First Search, Binary Tree |
| 1161 | Maximum Level Sum of a Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1261 | Find Elements in a Contaminated Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 1302 | Deepest Leaves Sum | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1305 | All Elements in Two Binary Search Trees | Medium | Tree, Depth-First Search, Binary Search Tree +2 |
| 1315 | Sum of Nodes with Even-Valued Grandparent | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1325 | Delete Leaves With a Given Value | Medium | Tree, Depth-First Search, Binary Tree |
| 1339 | Maximum Product of Splitted Binary Tree | Medium | Tree, Depth-First Search, Binary Tree |
| 1361 | Validate Binary Tree Nodes | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 1367 | Linked List in Binary Tree | Medium | Tree, Depth-First Search, Linked List +1 |
| 1372 | Longest ZigZag Path in a Binary Tree | Medium | Tree, Depth-First Search, Dynamic Programming +1 |
| 1382 | Balance a Binary Search Tree | Medium | Greedy, Tree, Depth-First Search +3 |
| 1448 | Count Good Nodes in Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1457 | Pseudo-Palindromic Paths in a Binary Tree | Medium | Bit Manipulation, Tree, Depth-First Search +2 |
| 1530 | Number of Good Leaf Nodes Pairs | Medium | Tree, Depth-First Search, Binary Tree |
| 1609 | Even Odd Tree | Medium | Tree, Breadth-First Search, Binary Tree |
| 2049 | Count Nodes With the Highest Score | Medium | Tree, Depth-First Search, Array +1 |
| 2096 | Step-By-Step Directions From a Binary Tree Node to Another | Medium | Tree, Depth-First Search, String +1 |
| 2196 | Create Binary Tree From Descriptions | Medium | Tree, Array, Hash Table +1 |
| 2265 | Count Nodes Equal to Average of Subtree | Medium | Tree, Depth-First Search, Binary Tree |
| 2385 | Amount of Time for Binary Tree to Be Infected | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2415 | Reverse Odd Levels of Binary Tree | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 2471 | Minimum Number of Operations to Sort a Binary Tree by Level | Medium | Tree, Breadth-First Search, Binary Tree |
| 2476 | Closest Nodes Queries in a Binary Search Tree | Medium | Tree, Depth-First Search, Binary Search Tree +3 |
| 2583 | Kth Largest Sum in a Binary Tree | Medium | Tree, Breadth-First Search, Binary Tree +1 |
| 2641 | Cousins in Binary Tree II | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2673 | Make Costs of Paths Equal in a Binary Tree | Medium | Greedy, Tree, Array +2 |
| 156 | Binary Tree Upside DownPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 250 | Count Univalue SubtreesPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 255 | Verify Preorder Sequence in Binary Search TreePremium | Medium | Stack, Tree, Binary Search Tree +4 |
| 285 | Inorder Successor in BSTPremium | Medium | Tree, Depth-First Search, Binary Search Tree +1 |
| 298 | Binary Tree Longest Consecutive SequencePremium | Medium | Tree, Depth-First Search, Binary Tree |
| 314 | Binary Tree Vertical Order TraversalPremium | Medium | Tree, Depth-First Search, Breadth-First Search +3 |
| 333 | Largest BST SubtreePremium | Medium | Tree, Depth-First Search, Binary Search Tree +2 |
| 366 | Find Leaves of Binary TreePremium | Medium | Tree, Depth-First Search, Binary Tree |
| 426 | Convert Binary Search Tree to Sorted Doubly Linked ListPremium | Medium | Stack, Tree, Depth-First Search +4 |
| 510 | Inorder Successor in BST IIPremium | Medium | Tree, Binary Search Tree, Binary Tree |
| 536 | Construct Binary Tree from StringPremium | Medium | Stack, Tree, Depth-First Search +2 |
| 545 | Boundary of Binary TreePremium | Medium | Tree, Depth-First Search, Binary Tree |
| 549 | Binary Tree Longest Consecutive Sequence IIPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 663 | Equal Tree PartitionPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 666 | Path Sum IVPremium | Medium | Tree, Depth-First Search, Array +2 |
| 742 | Closest Leaf in a Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 776 | Split BSTPremium | Medium | Tree, Binary Search Tree, Recursion +1 |
| 1120 | Maximum Average SubtreePremium | Medium | Tree, Depth-First Search, Binary Tree |
| 1214 | Two Sum BSTsPremium | Medium | Stack, Tree, Depth-First Search +4 |
| 1430 | Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
| 1485 | Clone Binary Tree With Random PointerPremium | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1586 | Binary Search Tree Iterator IIPremium | Medium | Stack, Tree, Design +3 |
| 1602 | Find Nearest Right Node in Binary TreePremium | Medium | Tree, Breadth-First Search, Binary Tree |
| 1612 | Check If Two Expression Trees are EquivalentPremium | Medium | Tree, Depth-First Search, Hash Table +2 |
| 1628 | Design an Expression Tree With Evaluate FunctionPremium | Medium | Stack, Tree, Design +3 |
| 1644 | Lowest Common Ancestor of a Binary Tree IIPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 1650 | Lowest Common Ancestor of a Binary Tree IIIPremium | Medium | Tree, Hash Table, Two Pointers +1 |
| 1660 | Correct a Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1666 | Change the Root of a Binary TreePremium | Medium | Tree, Depth-First Search, Binary Tree |
| 1676 | Lowest Common Ancestor of a Binary Tree IVPremium | Medium | Tree, Depth-First Search, Hash Table +1 |
| 1740 | Find Distance in a Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 1902 | Depth of BST Given Insertion OrderPremium | Medium | Tree, Binary Search Tree, Array +2 |
| 1973 | Count Nodes Equal to Sum of DescendantsPremium | Medium | Tree, Depth-First Search, Binary Tree |
| 2445 | Number of Nodes With Value OnePremium | Medium | Tree, Depth-First Search, Breadth-First Search +2 |
| 2764 | Is Array a Preorder of Some Binary TreePremium | Medium | Stack, Tree, Depth-First Search +1 |
| 2773 | Height of Special Binary TreePremium | Medium | Tree, Depth-First Search, Breadth-First Search +1 |
Hard (16)
| # | Problem | Difficulty | Topics |
|---|---|---|---|
| 124 | Binary Tree Maximum Path Sum | Hard | Tree, Depth-First Search, Dynamic Programming +1 |
| 297 | Serialize and Deserialize Binary Tree | Hard | Tree, Depth-First Search, Breadth-First Search +3 |
| 968 | Binary Tree Cameras | Hard | Tree, Depth-First Search, Dynamic Programming +1 |
| 987 | Vertical Order Traversal of a Binary Tree | Hard | Tree, Depth-First Search, Breadth-First Search +3 |
| 1028 | Recover a Tree From Preorder Traversal | Hard | Tree, Depth-First Search, String +1 |
| 1373 | Maximum Sum BST in Binary Tree | Hard | Tree, Depth-First Search, Binary Search Tree +2 |
| 1569 | Number of Ways to Reorder Array to Get Same BST | Hard | Tree, Union Find, Binary Search Tree +7 |
| 2458 | Height of Binary Tree After Subtree Removal Queries | Hard | Tree, Depth-First Search, Breadth-First Search +2 |
| 2509 | Cycle Length Queries in a Tree | Hard | Tree, Array, Binary Tree |
| 272 | Closest Binary Search Tree Value IIPremium | Hard | Stack, Tree, Depth-First Search +4 |
| 431 | Encode N-ary Tree to Binary TreePremium | Hard | Tree, Depth-First Search, Breadth-First Search +2 |
| 1597 | Build Binary Expression Tree From Infix ExpressionPremium | Hard | Stack, Tree, String +1 |
| 1932 | Merge BSTs to Create Single BST | Hard | Tree, Depth-First Search, Hash Table +2 |
| 2005 | Subtree Removal Game with Fibonacci TreePremium | Hard | Tree, Math, Dynamic Programming +2 |
| 2313 | Minimum Flips in Binary Tree to Get ResultPremium | Hard | Tree, Depth-First Search, Dynamic Programming +1 |
| 2792 | Count Nodes That Are Great EnoughPremium | Hard | Tree, Depth-First Search, Divide and Conquer +1 |
Keep exploring
All LeetCode topicsEvery tag with a page of its own, with the number of problems behind each.LeetCode patternsThe techniques themselves, with a Python template and complexity for each.Curated study listsBlind 75, NeetCode 150 and three more, grouped by pattern.Easy problemsStart here when the data structure is new rather than the problem.
Other topics
- Array1,569
- String672
- Hash Table588
- Math485
- Dynamic Programming481
- Sorting392
- Greedy346
- Depth-First Search289
- Binary Search253
- Database249
- Tree225
- Breadth-First Search223
- Matrix216
- Two Pointers201
- Bit Manipulation194
- Heap (Priority Queue)163
- Prefix Sum157
- Stack157
- Simulation144
- Graph138
- Counting126
- Design122
- Sliding Window116
- Backtracking105
When the Binary Tree problem arrives live
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