vector<string> split(string str) {
    vector<string> res;
    char *token;
    char *text = (char *)str.c_str();
    token = strtok_r(text, " ", &text);
    while(token) {
        res.push_back(token);
        token = strtok_r(text, " " , &text);
    }
    return res;
}