[Leetcode] Maximum Depth of Binary Tree

/** * 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) {        // Start typing your C/C++ solution below        // DO NOT write int main() function        if (!root) return NULL;                if (!root->left && !root->right) return 1;                int left = INT_MIN;        int right = INT_MIN;                if (root->left)            left = maxDepth(root->left) + 1;                    if (root->right)            right = maxDepth(root->right) + 1;                    return max(left, right);    }};