Maximum Depth of Binary Tree

easyTests passed 2026-11-11v1.0.0
TC: O(N)|SC: O(H)
TreesOriginal Statement (leetcode).md

1. Core Invariant / The Trick

Post-order recurrence: an empty tree has depth `0`; otherwise `1 + max(maxDepth(left), maxDepth(right))`.

2. Complexity Bounds & Proof

Every node is visited once in post-order DFS with O(H) call stack depth.

3. Minimal Idiomatic Code

def maxDepth(root: Optional[TreeNode]) -> int:
    if not root:
        return 0
    return 1 + max(maxDepth(root.left), maxDepth(root.right))

4. Failure Modes & Interview Follow-ups

Pitfalls:- Off-by-one confusion between depth by nodes (root = 1) vs height by edges (root = 0).
Follow-ups:- Minimum Depth of Binary Tree prefers BFS so the first leaf encountered terminates immediately without scanning deeper subtrees.

Personal Notes & Scratchpad (Local-First Yjs CRDT)

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Related Invariants

Diameter of Binary Tree (O(N))Balanced Binary Tree (O(N))
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