Diameter of Binary Tree – Solution & Complexity
Solution Walkthrough
1. Recognize the Pattern
The key pattern is: Bottom-up DFS height computation that updates a running best at every node. Identify the state and invariant before coding.
2. Build the Algorithm
Advance one state transition at a time. Mark or update state before exploring dependent work.
3. Check Edge Cases
Test empty or minimal input, skewed shapes, duplicates where allowed, and impossible outcomes.
4. Solution and Complexity
Time: O(n). Space: O(h) for the recursion stack.
All 5 languages below run and submit against the remote judge for this problem — Java/Go/Rust use the same real TreeNode structural-type support the judge added for the rest of the linked-list/tree track.
