Diameter of Binary Tree
Part of Practice: Recursive Foundations
Given the root of a binary tree, return the diameter: the number of edges on the longest path between any two nodes in the tree. The path does not have to pass through the root — it can live entirely inside one subtree.
The tree has 1 to 10,000 nodes. Note the answer counts edges, not nodes: a path of 4 nodes has length 3.
Examples
- Input:
- root = [1,2,3,4,5]
- Output:
- 3
The longest path is 4 → 2 → 5 or 4 → 2 → 1 → 3, both spanning 3 edges.
- Input:
- root = [1,2]
- Output:
- 1
- Input:
- root = [1]
- Output:
- 0
A single node has no edges, so the diameter is 0.
Hints
One at a time — struggle first, peek second.
Your thinking space — verify on LeetCode, then mark it.