Maximum Depth of Binary Tree
Part of Practice: Recursive Foundations
Given the root of a binary tree, return its maximum depth: the number of nodes on the longest downward path from the root to any leaf (a node with no children). An empty tree has depth 0 and a single node has depth 1.
The tree has at most 10,000 nodes.
Examples
- Input:
- root = [3,9,20,null,null,15,7]
- Output:
- 3
The longest root-to-leaf path is 3 → 20 → 15 (or 3 → 20 → 7): three nodes.
- Input:
- root = [1,null,2]
- Output:
- 2
- Input:
- root = []
- Output:
- 0
Hints
One at a time — struggle first, peek second.
Your thinking space — verify on LeetCode, then mark it.