可能是因为我是按难度顺序刷的原因，这个其实在之前的几道题里面已经写过了。题目如下：

Given a binary tree, find its maximum depth.

The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.

然后就直接拿之前的代码了：

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:    int maxDepth(TreeNode *root) {        if (root == NULL)	 		return 0;	 	else	 	{	 		int aspros = maxDepth(root->left);	 		int defteros = maxDepth(root->right);	 		return 1 + (aspros>defteros ? aspros : defteros);	 	}    }};

非常简单，重复复用。

[leetcode] 8. Maximum Depth of Binary Tree