Maximum Depth of Binary Tree

/** * Definition for binary tree * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    public int maxDepth(TreeNode root) {        if(null == root) return 0;        return Math.max(maxDepth(root.left), maxDepth(root.right))+1;    }}