最长的公共前缀

string longestCommonPrefix(vector<string>& strs) 
{
        string prefix = "";
        if (strs.size() == 0) return prefix;

        for (int i = 0; i < strs[0].size(); i++)
        {
            int j = 1;
            for (; j < strs.size()&&strs[j].size()>i; j++)
            {
                if (strs[j][i] != strs[0][i])
                    return prefix;//此return将推出内置的for循环
            }
            if (j == strs.size()) prefix += strs[0][i];
        }
        return prefix;
 }