二叉树的最大深度（简单）

思路：深度优先搜索

/*** 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;}}
}