68. Longest Common Prefix

string commonPrefix(string s1, string s2){
    if(s1 == "" || s2 == "") return "";
    int k = 0, len1 = s1.length();
    while(k < len1 && s1[k] == s2[k]) ++k;
    return s1.substr(0, k);
}
    
class Solution {
public:
    string longestCommonPrefix(vector<string> &strs) {
        int len = strs.size();
        if(len == 0) return "";
        string s(strs[0]);
        for(int i = 1; i < len; ++i){
            if(s == "") return s;
            s = commonPrefix(s, strs[i]);
        }
        return s;
    }
};