Skip to main content

12. Maximum Depth of Binary Tree

easyAsked at Gojek

Return the maximum depth (number of nodes on the longest root-to-leaf path) of a binary tree.

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

Problem

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

Constraints

  • The number of nodes is in [0, 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

Walk level by level with a queue and count levels.

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

Tradeoff:

2. Recursive max

Depth of a node is one plus the max depth of its children. Empty tree is depth zero.

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

Tradeoff:

Gojek-specific tips

Gojek favors candidates who name the trade-off between BFS memory and DFS depth, since dispatch graphs in their multi-service stack can be both deep and wide depending on the city.

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

Practice these live with InterviewChamp.AI →