Binary Tree LeetCode Problems: All 174,
With Python Solutions

Every problem in this library that LeetCode tags Binary Tree. 128 of them carry a complete Python solution, a worked example and the time and space complexity of the approach.

Get Stealth Interview

Easy: 38
Medium: 120
Hard: 16

1 pattern

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 TraversalChoose the order — preorder, inorder, postorder, level — and the problem solves itself.

Eyes only

When the Binary Tree problem arrives live.

In the live round, Stealth Interview reads the problem off your screen, returns a working solution with a step-by-step explanation and its time and space complexity, and transcribes what the interviewer says. It's a desktop app for macOS and Windows, invisible to screen sharing.

Get Stealth Interview See pricing

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

Technical interview · 45 minsolution.pyShared editor · Python 3Longest substring without repeatsMediumGiven a string s, return the length of the longest contiguous substring in which every character is unique.s = "abcabcbb"
→ 31def length_of_longest_substring(s: str) -> int:2 last_seen = {}3 left = best = 04 for right, ch in enumerate(s):5 if ch in last_seen and last_seen[ch] >= left:

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 Terra

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

90%Subscription

python

Please analyze this context and help me answer the question or solve the problem.

python

def length_of_longest_substring(s: str) -> int:    last_seen = {}                    # char -> index    left = best = 0    for right, ch in enumerate(s):        if ch in last_seen and last_seen[ch] >= left:            left = last_seen[ch] + 1  # jump past it        last_seen[ch] = right        best = max(best, right - left + 1)    return best    last_seen = {}                    # char -> index

Approach

At each index r, the window's left edge is:

left r = max (left r -1, last[s r] + 1)

Time O(n): each character enters and leaves the window once.
Space O(min(n, k)): k is the size of the character set.

Type your message...

GPT-6.1 TerraClear chat

Primary display

QuitEscHide+QCapture+PCrop+OSubmit+EnterPress to get answerLeft/Right+Up/Down+

Binary Tree problems by difficulty

Problems with a complete Python solution are listed first, then by ascending problem number.

Easy (38)

Easy problems
No.	Problem	Topics
0094	Binary Tree Inorder Traversal	Stack, Tree, Depth-First Search +1
0100	Same Tree	Tree, Depth-First Search, Breadth-First Search +1
0101	Symmetric Tree	Tree, Depth-First Search, Breadth-First Search +1
0104	Maximum Depth of Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0108	Convert Sorted Array to Binary Search Tree	Tree, Binary Search Tree, Array +2
0110	Balanced Binary Tree	Tree, Depth-First Search, Binary Tree
0111	Minimum Depth of Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0112	Path Sum	Tree, Depth-First Search, Breadth-First Search +1
0144	Binary Tree Preorder Traversal	Stack, Tree, Depth-First Search +1
0145	Binary Tree Postorder Traversal	Stack, Tree, Depth-First Search +1
0222	Count Complete Tree Nodes	Bit Manipulation, Tree, Binary Search +1
0226	Invert Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0257	Binary Tree Paths	Tree, Depth-First Search, String +2
0404	Sum of Left Leaves	Tree, Depth-First Search, Breadth-First Search +1
0501	Find Mode in Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +1
0530	Minimum Absolute Difference in BST	Tree, Depth-First Search, Breadth-First Search +2
0543	Diameter of Binary Tree	Tree, Depth-First Search, Binary Tree
0563	Binary Tree Tilt	Tree, Depth-First Search, Binary Tree
0572	Subtree of Another Tree	Tree, Depth-First Search, Binary Tree +2
0617	Merge Two Binary Trees	Tree, Depth-First Search, Breadth-First Search +1
0637	Average of Levels in Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0653	Two Sum IV - Input is a BST	Tree, Depth-First Search, Breadth-First Search +4
0671	Second Minimum Node In a Binary Tree	Tree, Depth-First Search, Binary Tree
0700	Search in a Binary Search Tree	Tree, Binary Search Tree, Binary Tree
0703	Kth Largest Element in a Stream	Tree, Design, Binary Search Tree +3
0783	Minimum Distance Between BST Nodes	Tree, Depth-First Search, Breadth-First Search +2
0872	Leaf-Similar Trees	Tree, Depth-First Search, Binary Tree
0897	Increasing Order Search Tree	Stack, Tree, Depth-First Search +2
0938	Range Sum of BST	Tree, Depth-First Search, Binary Search Tree +1
0965	Univalued Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0993	Cousins in Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
1022	Sum of Root To Leaf Binary Numbers	Tree, Depth-First Search, Binary Tree
1379	Find a Corresponding Node of a Binary Tree in a Clone of That Tree	Tree, Depth-First Search, Breadth-First Search +1
2236	Root Equals Sum of Children	Tree, Binary Tree
2331	Evaluate Boolean Binary Tree	Tree, Depth-First Search, Binary Tree
0270	Closest Binary Search Tree ValuePremium	Tree, Depth-First Search, Binary Search Tree +2
1469	Find All The Lonely NodesPremium	Tree, Depth-First Search, Breadth-First Search +1
2689	Extract Kth Character From The Rope TreePremium	Tree, Depth-First Search, Binary Tree

Medium (120)

Medium problems
No.	Problem	Topics
0095	Unique Binary Search Trees II	Tree, Binary Search Tree, Dynamic Programming +2
0096	Unique Binary Search Trees	Tree, Binary Search Tree, Math +2
0098	Validate Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +1
0099	Recover Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +1
0102	Binary Tree Level Order Traversal	Tree, Breadth-First Search, Binary Tree
0103	Binary Tree Zigzag Level Order Traversal	Tree, Breadth-First Search, Binary Tree
0105	Construct Binary Tree from Preorder and Inorder Traversal	Tree, Array, Hash Table +2
0106	Construct Binary Tree from Inorder and Postorder Traversal	Tree, Array, Hash Table +2
0107	Binary Tree Level Order Traversal II	Tree, Breadth-First Search, Binary Tree
0109	Convert Sorted List to Binary Search Tree	Tree, Binary Search Tree, Linked List +2
0113	Path Sum II	Tree, Depth-First Search, Backtracking +1
0114	Flatten Binary Tree to Linked List	Stack, Tree, Depth-First Search +2
0116	Populating Next Right Pointers in Each Node	Tree, Depth-First Search, Breadth-First Search +2
0117	Populating Next Right Pointers in Each Node II	Tree, Depth-First Search, Breadth-First Search +2
0129	Sum Root to Leaf Numbers	Tree, Depth-First Search, Binary Tree
0173	Binary Search Tree Iterator	Stack, Tree, Design +3
0199	Binary Tree Right Side View	Tree, Depth-First Search, Breadth-First Search +1
0230	Kth Smallest Element in a BST	Tree, Depth-First Search, Binary Search Tree +1
0235	Lowest Common Ancestor of a Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +1
0236	Lowest Common Ancestor of a Binary Tree	Tree, Depth-First Search, Binary Tree
0331	Verify Preorder Serialization of a Binary Tree	Stack, Tree, String +1
0337	House Robber III	Tree, Depth-First Search, Dynamic Programming +1
0437	Path Sum III	Tree, Depth-First Search, Binary Tree
0449	Serialize and Deserialize BST	Tree, Depth-First Search, Breadth-First Search +4
0450	Delete Node in a BST	Tree, Binary Search Tree, Binary Tree
0508	Most Frequent Subtree Sum	Tree, Depth-First Search, Hash Table +1
0513	Find Bottom Left Tree Value	Tree, Depth-First Search, Breadth-First Search +1
0515	Find Largest Value in Each Tree Row	Tree, Depth-First Search, Breadth-First Search +1
0538	Convert BST to Greater Tree	Tree, Depth-First Search, Binary Search Tree +1
0606	Construct String from Binary Tree	Tree, Depth-First Search, String +1
0623	Add One Row to Tree	Tree, Depth-First Search, Breadth-First Search +1
0652	Find Duplicate Subtrees	Tree, Depth-First Search, Hash Table +1
0654	Maximum Binary Tree	Stack, Tree, Array +3
0655	Print Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0662	Maximum Width of Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
0669	Trim a Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +1
0687	Longest Univalue Path	Tree, Depth-First Search, Binary Tree
0701	Insert into a Binary Search Tree	Tree, Binary Search Tree, Binary Tree
0814	Binary Tree Pruning	Tree, Depth-First Search, Binary Tree
0863	All Nodes Distance K in Binary Tree	Tree, Depth-First Search, Breadth-First Search +2
0865	Smallest Subtree with all the Deepest Nodes	Tree, Depth-First Search, Breadth-First Search +2
0889	Construct Binary Tree from Preorder and Postorder Traversal	Tree, Array, Hash Table +2
0894	All Possible Full Binary Trees	Tree, Recursion, Memoization +2
0919	Complete Binary Tree Inserter	Tree, Breadth-First Search, Design +1
0951	Flip Equivalent Binary Trees	Tree, Depth-First Search, Binary Tree
0958	Check Completeness of a Binary Tree	Tree, Breadth-First Search, Binary Tree
0971	Flip Binary Tree To Match Preorder Traversal	Tree, Depth-First Search, Binary Tree
0979	Distribute Coins in Binary Tree	Tree, Depth-First Search, Binary Tree
0988	Smallest String Starting From Leaf	Tree, Depth-First Search, String +2
0998	Maximum Binary Tree II	Tree, Binary Tree
1008	Construct Binary Search Tree from Preorder Traversal	Stack, Tree, Binary Search Tree +3
1026	Maximum Difference Between Node and Ancestor	Tree, Depth-First Search, Binary Tree
1038	Binary Search Tree to Greater Sum Tree	Tree, Depth-First Search, Binary Search Tree +1
1080	Insufficient Nodes in Root to Leaf Paths	Tree, Depth-First Search, Binary Tree
1104	Path In Zigzag Labelled Binary Tree	Tree, Math, Binary Tree
1110	Delete Nodes And Return Forest	Tree, Depth-First Search, Array +2
1123	Lowest Common Ancestor of Deepest Leaves	Tree, Depth-First Search, Breadth-First Search +2
1145	Binary Tree Coloring Game	Tree, Depth-First Search, Binary Tree
1161	Maximum Level Sum of a Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
1261	Find Elements in a Contaminated Binary Tree	Tree, Depth-First Search, Breadth-First Search +3
1302	Deepest Leaves Sum	Tree, Depth-First Search, Breadth-First Search +1
1305	All Elements in Two Binary Search Trees	Tree, Depth-First Search, Binary Search Tree +2
1315	Sum of Nodes with Even-Valued Grandparent	Tree, Depth-First Search, Breadth-First Search +1
1325	Delete Leaves With a Given Value	Tree, Depth-First Search, Binary Tree
1339	Maximum Product of Splitted Binary Tree	Tree, Depth-First Search, Binary Tree
1361	Validate Binary Tree Nodes	Tree, Depth-First Search, Breadth-First Search +3
1367	Linked List in Binary Tree	Tree, Depth-First Search, Linked List +1
1372	Longest ZigZag Path in a Binary Tree	Tree, Depth-First Search, Dynamic Programming +1
1382	Balance a Binary Search Tree	Greedy, Tree, Depth-First Search +3
1448	Count Good Nodes in Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
1457	Pseudo-Palindromic Paths in a Binary Tree	Bit Manipulation, Tree, Depth-First Search +2
1530	Number of Good Leaf Nodes Pairs	Tree, Depth-First Search, Binary Tree
1609	Even Odd Tree	Tree, Breadth-First Search, Binary Tree
2049	Count Nodes With the Highest Score	Tree, Depth-First Search, Array +1
2096	Step-By-Step Directions From a Binary Tree Node to Another	Tree, Depth-First Search, String +1
2196	Create Binary Tree From Descriptions	Tree, Array, Hash Table +1
2265	Count Nodes Equal to Average of Subtree	Tree, Depth-First Search, Binary Tree
2385	Amount of Time for Binary Tree to Be Infected	Tree, Depth-First Search, Breadth-First Search +2
2415	Reverse Odd Levels of Binary Tree	Tree, Depth-First Search, Breadth-First Search +1
2471	Minimum Number of Operations to Sort a Binary Tree by Level	Tree, Breadth-First Search, Binary Tree
2476	Closest Nodes Queries in a Binary Search Tree	Tree, Depth-First Search, Binary Search Tree +3
2583	Kth Largest Sum in a Binary Tree	Tree, Breadth-First Search, Binary Tree +1
2641	Cousins in Binary Tree II	Tree, Depth-First Search, Breadth-First Search +2
2673	Make Costs of Paths Equal in a Binary Tree	Greedy, Tree, Array +2
0156	Binary Tree Upside DownPremium	Tree, Depth-First Search, Binary Tree
0250	Count Univalue SubtreesPremium	Tree, Depth-First Search, Binary Tree
0255	Verify Preorder Sequence in Binary Search TreePremium	Stack, Tree, Binary Search Tree +4
0285	Inorder Successor in BSTPremium	Tree, Depth-First Search, Binary Search Tree +1
0298	Binary Tree Longest Consecutive SequencePremium	Tree, Depth-First Search, Binary Tree
0314	Binary Tree Vertical Order TraversalPremium	Tree, Depth-First Search, Breadth-First Search +3
0333	Largest BST SubtreePremium	Tree, Depth-First Search, Binary Search Tree +2
0366	Find Leaves of Binary TreePremium	Tree, Depth-First Search, Binary Tree
0426	Convert Binary Search Tree to Sorted Doubly Linked ListPremium	Stack, Tree, Depth-First Search +4
0510	Inorder Successor in BST IIPremium	Tree, Binary Search Tree, Binary Tree
0536	Construct Binary Tree from StringPremium	Stack, Tree, Depth-First Search +2
0545	Boundary of Binary TreePremium	Tree, Depth-First Search, Binary Tree
0549	Binary Tree Longest Consecutive Sequence IIPremium	Tree, Depth-First Search, Binary Tree
0663	Equal Tree PartitionPremium	Tree, Depth-First Search, Binary Tree
0666	Path Sum IVPremium	Tree, Depth-First Search, Array +2
0742	Closest Leaf in a Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +1
0776	Split BSTPremium	Tree, Binary Search Tree, Recursion +1
1120	Maximum Average SubtreePremium	Tree, Depth-First Search, Binary Tree
1214	Two Sum BSTsPremium	Stack, Tree, Depth-First Search +4
1430	Check If a String Is a Valid Sequence from Root to Leaves Path in a Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +1
1485	Clone Binary Tree With Random PointerPremium	Tree, Depth-First Search, Breadth-First Search +2
1586	Binary Search Tree Iterator IIPremium	Stack, Tree, Design +3
1602	Find Nearest Right Node in Binary TreePremium	Tree, Breadth-First Search, Binary Tree
1612	Check If Two Expression Trees are EquivalentPremium	Tree, Depth-First Search, Hash Table +2
1628	Design an Expression Tree With Evaluate FunctionPremium	Stack, Tree, Design +3
1644	Lowest Common Ancestor of a Binary Tree IIPremium	Tree, Depth-First Search, Binary Tree
1650	Lowest Common Ancestor of a Binary Tree IIIPremium	Tree, Hash Table, Two Pointers +1
1660	Correct a Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +2
1666	Change the Root of a Binary TreePremium	Tree, Depth-First Search, Binary Tree
1676	Lowest Common Ancestor of a Binary Tree IVPremium	Tree, Depth-First Search, Hash Table +1
1740	Find Distance in a Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +2
1902	Depth of BST Given Insertion OrderPremium	Tree, Binary Search Tree, Array +2
1973	Count Nodes Equal to Sum of DescendantsPremium	Tree, Depth-First Search, Binary Tree
2445	Number of Nodes With Value OnePremium	Tree, Depth-First Search, Breadth-First Search +2
2764	Is Array a Preorder of Some ‌Binary TreePremium	Stack, Tree, Depth-First Search +1
2773	Height of Special Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +1

Hard (16)

Hard problems
No.	Problem	Topics
0124	Binary Tree Maximum Path Sum	Tree, Depth-First Search, Dynamic Programming +1
0297	Serialize and Deserialize Binary Tree	Tree, Depth-First Search, Breadth-First Search +3
0968	Binary Tree Cameras	Tree, Depth-First Search, Dynamic Programming +1
0987	Vertical Order Traversal of a Binary Tree	Tree, Depth-First Search, Breadth-First Search +3
1028	Recover a Tree From Preorder Traversal	Tree, Depth-First Search, String +1
1373	Maximum Sum BST in Binary Tree	Tree, Depth-First Search, Binary Search Tree +2
1569	Number of Ways to Reorder Array to Get Same BST	Tree, Union Find, Binary Search Tree +7
2458	Height of Binary Tree After Subtree Removal Queries	Tree, Depth-First Search, Breadth-First Search +2
2509	Cycle Length Queries in a Tree	Tree, Array, Binary Tree
0272	Closest Binary Search Tree Value IIPremium	Stack, Tree, Depth-First Search +4
0431	Encode N-ary Tree to Binary TreePremium	Tree, Depth-First Search, Breadth-First Search +2
1597	Build Binary Expression Tree From Infix ExpressionPremium	Stack, Tree, String +1
1932	Merge BSTs to Create Single BST	Tree, Depth-First Search, Hash Table +2
2005	Subtree Removal Game with Fibonacci TreePremium	Tree, Math, Dynamic Programming +2
2313	Minimum Flips in Binary Tree to Get ResultPremium	Tree, Depth-First Search, Dynamic Programming +1
2792	Count Nodes That Are Great EnoughPremium	Tree, Depth-First Search, Divide and Conquer +1

How Binary Tree problems are solved

When the Binary Tree problem arrives live.

Approach

Approach

Approach

Binary Tree problems by difficulty

Easy (38)38

Medium (120)120

Hard (16)16

Keep exploring

Easy (38)

Medium (120)

Hard (16)