leetcode-14- longest common prefix

class Solution {
public:
    string (vector<string>& strs) {
        if(strs.empty()) return "";
        int min_size = strs[0].length();
        for( int i = 0;i<strs.size();i++){
            if(strs[i].length()<min_size)
                min_size = strs[i].length();
        }
        int len = 0;
        int flag = 1;
        for(int i=0;i<min_size;i++){
            for(int j=0;j<strs.size();j++){
                if(strs[j][i]!=strs[0][i])
                flag =0;
            }
            if(flag)
                len++;
            else break;
        }
        return strs[0].substr(0,len);
    }
};