1 /**
 2  * Definition for a binary tree node.
 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         }
15        
16         int leftDepth = maxDepth(root.left);   //计算左子树的深度
17         int rightDepth = maxDepth(root.right); //计算右子树的深度
18         
19         return 1 + (leftDepth > rightDepth ? leftDepth : rightDepth);
20     }
21 }