#48 Easy Time O(n) Space O(n) Animated

Diameter of Binary Tree

Find the length of the diameter of a binary tree.

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Tutor Mode Build the mental model before you memorize the code.

1 Predict
2 Trace
3 Explain
4 Implement

Pattern Tree traversal with recursive contracts

Ask each subtree for exactly the information its parent needs, then combine the two answers.

Approach: DFS (Recursion)

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Core Insight

Ask each subtree for exactly the information its parent needs, then combine the two answers.

Common Pitfall

Define the base case before combining left and right subtree results.

Description

Find the length of the diameter of a binary tree.

Constraints

Time Complexity: O(n)
Space Complexity: O(n)

Solution — DFS (Recursion)

TimeO(n) SpaceO(n)

Implementation Plan

Translate the invariant into these small, testable moves.

Define what one recursive call returns.
Handle an empty node.
Recurse into children.
Combine the child results at the current node.

def diameterOfBinaryTree(root):
    res = 0
    
    def dfs(node):
        nonlocal res
        if not node:
            return 0
            
        left = dfs(node.left)
        right = dfs(node.right)
        
        res = max(res, left + right)
        return 1 + max(left, right)
        
    dfs(root)
    return res

Maximum Depth of Binary Tree

Balanced Binary Tree

Diameter of Binary Tree

Steps

Description

Constraints

Tags

Solution — DFS (Recursion)