Maximum Depth of Binary Tree

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.

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     int maxDepth(TreeNode *root) {
13         if(!root)
14             return 0;
15         return max(maxDepth(root->left),maxDepth(root->right))+1;
16     }
17     
18 };

空就返回0，否则加深度1，递归。