Longest Common Prefix

Write a function to find the longest common prefix string amongst an array of strings.

class Solution {
public:
    string longestCommonPrefix(vector<string>& strs) {
        string res = "";
        if(!strs.empty()){
            for(int i = 0; i < strs[0].size(); i++){

                for(int j = 1; j < strs.size(); j++){
                    if(strs[j][i] != strs[0][i])
                        return res;
                }

                res += strs[0][i];
            }

        }

        return res;
    }
};