int shortest_way (string src , string target)
{

    unordered_map <char , vector <int>> char_idx;

       for (int i = 0 ; i < src.size(); i++)
       {
           char c = src[i];
           char_idx[c].push_back(i);
       }
        int res = 0;
    int last = -1;
    for (int i = 0 ; i  < target.size(); i++)
    {
        char c = target[i];
        //char in target and not in src
        if (char_idx.find(c) == char_idx.end())
            return -1;
        vector <int> vec = char_idx[c];
        int idx = upper_bound(vec.begin(), vec.end(), last) - vec.begin();

        if (idx == vec.size())
        {

            last = -1;
            i--; // this element is not found
            res++;
            continue;
        }
        last = vec[idx];
        if ( last + 1 == src.size())
        {
            last = -1;
            res++;
        }


    }

    return res;

}

int main() {
    cout << shortest_way ("abc","abcbc");
}