LeetCode-Minimum Depth of Binary Tree

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.

/**
 * 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 minDepth(TreeNode *root) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if(root==NULL)return 0;
        if(root->left==NULL&&root->right==NULL){
            return 1;
        }
        int ret1=minDepth(root->left);
        int ret2=minDepth(root->right);
        if(ret1==0)return ret2+1;
        else if(ret2==0)return ret1+1;
        else return min(ret1,ret2)+1;
    }
};