代码：

0117

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