Maximum Depth of Binary Tree

1/**
2 * Definition for a binary tree node.
3 * public class TreeNode {
4 *     int val;
5 *     TreeNode left;
6 *     TreeNode right;
7 *     TreeNode() {}
8 *     TreeNode(int val) { this.val = val; }
9 *     TreeNode(int val, TreeNode left, TreeNode right) {
10 *         this.val = val;
11 *         this.left = left;
12 *         this.right = right;
13 *     }
14 * }
15 */
16class Solution {
17    private int traverse(TreeNode root, int depth) {
18        if (root == null) {
19            return depth;
20        }
21
22        int leftDepth = traverse(root.left, depth + 1);
23        int rightDepth = traverse(root.right, depth + 1);
24
25        return Math.max(leftDepth, rightDepth);
26    }
27    public int maxDepth(TreeNode root) {
28        return traverse(root, 0);
29    }
30}