class Solution {
public:
string longestCommonPrefix(vector<string>& strs) {
string res;
if (strs.empty()) return res;
for (int i = 0;; i ++ ) {
if (i >= strs[0].size()) return res;
char c = strs[0][i];
int flag=1;
for (auto& str: strs){
if (i< str.size()&&str[i] == c)
flag=1;
else{
flag=0;
break;
}
}
if(flag==0)return res;
else res+=c;
}
return res;
}
};