Maximum Depth of Binary Tree — Practice

Problem

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

Example 1

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

Output: 3

Explanation: The longest path is 3 -> 20 -> 15 (or 7), 3 nodes deep.

Hint 1

A tree's depth is naturally defined recursively: 1 + the deeper of its two subtrees' depths.

Hint 2

The base case (null node) has depth 0 — this is what makes the recursion terminate correctly.

public int maxDepth(TreeNode root) {
    if (root == null) return 0;
    return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
}

Time: O(n) · Space: O(h)