1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     public int maxDepth(TreeNode root) {
12         if(root == null)
13             return 0;
14         int max_left = maxDepth(root.left);
15         int max_right = maxDepth(root.right);
16         if(max_left>max_right)
17             return max_left+1;
18         else
19             return max_right +1;
20         
21     }
22 }