Skip to main content

12. Maximum Depth of Binary Tree

easyAsked at Indeed

Compute the maximum depth of a binary tree — Indeed's recursive-base-case warmup before facet-tree depth limits in category browse.

By Alex Chen, Founder, InterviewChamp.AI · Last verified

Problem

Given the root of a binary tree, return its maximum depth — the number of nodes along the longest path from the root down to the farthest leaf.

Constraints

  • 0 <= nodes <= 10^4
  • -100 <= node.val <= 100

Examples

Example 1

Input
root = [3,9,20,null,null,15,7]
Output
3

Example 2

Input
root = [1,null,2]
Output
2

Approaches

1. BFS level count

BFS level by level, incrementing depth per layer.

Time
O(n)
Space
O(n)
if (!root) return 0;
let q = [root], d = 0;
while (q.length) {
  q = q.flatMap(n => [n.left, n.right].filter(Boolean));
  d++;
}
return d;

Tradeoff:

2. Recursive max

Depth = 1 + max(depth(left), depth(right)).

Time
O(n)
Space
O(h)
function maxDepth(root) {
  if (!root) return 0;
  return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
}

Tradeoff:

Indeed-specific tips

Indeed cares about the empty-tree base case — they apply max-depth as a guardrail against runaway recursive crawls on its category trees.

Solve it now

Free. No sign-up. Python and JavaScript run instantly in your browser.

Output

Press Run or Cmd+Enter to execute

Practice these live with InterviewChamp.AI

Drill Maximum Depth of Binary Tree and other Indeed interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →