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7. Maximum Depth of Binary Tree

easyAsked at Flipkart

Compute the height of a binary tree — Flipkart uses this as a recursion sanity check before harder catalog-tree traversals.

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. Iterative BFS

Level-order traversal, increment depth per level.

Time
O(n)
Space
O(n)
// queue with [node, depth]; track max depth observed

Tradeoff:

2. Recursive DFS

Return 1 + max(left depth, right depth). Cleanest implementation; uses O(h) stack.

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

Tradeoff:

Flipkart-specific tips

Flipkart screeners listen for the iterative fallback discussion — their production catalog trees are deep enough that they have hit recursion limits in real services.

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Output

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