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) {        if(root==NULL)        {            return 0;        }        int ldepth=maxDepth(root->left);        int rdepth=maxDepth(root->right);        return ldepth>rdepth?ldepth+1:rdepth+1;    }};