二叉树的最大深度（LintCode）

1
/ \
2   3
/ \
4   5

3

/**
* Definition of TreeNode:
* class TreeNode {
* public:
*     int val;
*     TreeNode *left, *right;
*     TreeNode(int val) {
*         this->val = val;
*         this->left = this->right = NULL;
*     }
* }
*/
class Solution
{
public:
/**
* @param root: The root of binary tree.
* @return: An integer
*/
int maxDepth(TreeNode *root)
{
if (root == NULL)
{
return 0;
}
int left = maxDepth(root->left);
int right = maxDepth(root->right);
return (left > right) ? left + 1 : right + 1;
}
};