思路：求二叉树的深度，想到左右子树递归
代码：
/**
public class TreeNode {
int val = 0;
TreeNode left = null;
TreeNode right = null;
public TreeNode(int val) {
this.val = val;
}
}
*/
public class Solution {
public int TreeDepth(TreeNode root) {
if(root == null){
return 0;
}
int deepth = 1;
int left = this.TreeDepth(root.left);
int right = this.TreeDepth(root.right);
deepth += left > right?left:right;
return deepth;
}
}end
