string replaceSpaces(string &str) {
        size_t t;
        while((t=str.find(' '))!=string::npos){
            str.replace(t,1,"%20");
        }
        return str;
    }

string replaceSpaces(string &str) {
        string res;
        for (auto x : str)
            if (x == ' ')
                res += "%20";
            else
                res += x;
        return res;
    }