Skip to main content

3. Maximum Depth of Binary Tree

easyAsked at Rappi

Compute the height of a binary tree — Rappi frames this as measuring the longest hand-off chain in a multi-courier relay routing graph.

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 furthest 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. Iterative BFS

Level-order traversal incrementing a depth counter per level.

Time
O(n)
Space
O(n)
let depth = 0, q = root ? [root] : [];
while (q.length) {
  const next = [];
  for (const n of q) { if (n.left) next.push(n.left); if (n.right) next.push(n.right); }
  depth++; q = next;
}
return depth;

Tradeoff:

2. Recursive DFS

Depth of a node is 1 plus the max depth of its children; base case empty subtree is 0.

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

Tradeoff:

Rappi-specific tips

Rappi grades for the recursive solution — they want to see you reason about hand-off chain length the same way their dispatch graph computes worst-case ETA.

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 Rappi interview questions under real-loop conditions with instant feedback on your reasoning, complexity claims, and code.

Practice these live with InterviewChamp.AI →