最长公共前缀

class Solution {
public:
    string longestCommonPrefix(vector <string> &strs) {
        std:
        string res = strs[0];
        for (int i = 1; i < strs.size(); i++) {
            std::string tmp;
            for (int k = 0; k < res.size() || k < strs[i].size(); ++k) {
                if (res[k] == strs[i][k])
                    tmp.push_back(res[k]);
                else
                    break;
            }
            res = tmp;
        }
        return res;
    }
};