最长的共同前缀

string longestCommonPrefix(vector<string>& strs) {
    if (strs.empty()){
        return string();
    }
    
    vector<string::iterator> its;
    for_each(strs.begin(), strs.end(), [&](string& s){its.push_back(s.begin());});
    const auto len = its.size();
    
    for (;;){
        const auto key = *its[0];
        for (size_t i = 0; i != len; ++i){
            if (its[i] == strs[i].end() || *its[i] != key){
                return string(strs[i].begin(), its[i]);
            }
        }
        for_each(its.begin(), its.end(), [](string::iterator& it){++it;});
    }
}