Leetcode 104. Maximum Depth of Binary Tree

求树的最大深度，如果树为空，则返回0
否则返回左最大深度和右最大深度的最大值，进行加一

/**
 * Definition for a binary tree node.
 * 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),maxDepth(root->right)) + 1;
    }
};