Maximum Depth of Binary Tree 二叉树的最大深度（重）

问题：

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.
解答：利用递归求解，求出左右子树的深度，然后选择深度较大的那个+1，为该树的最大深度。

* 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;
return max((maxDepth(root->left)+1),(maxDepth(root->right)+1));
}
};