minimum-depth-of-binary-tree leetcode C++

Given a binary tree, find its minimum depth.The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

C++

class Solution {
public:
    //run:12ms memory:884k
    int run(TreeNode *root) {
        if (NULL == root) return 0;
        if (NULL == root->left && NULL == root->right) return 1;
        if (NULL == root->left) return run(root->right) + 1;
        else if(root->right == NULL) return run(root->left) + 1;
        else return  min(run(root->left),run(root->right)) + 1;
    }
};