Word Abbreviation

http://shibaili.blogspot.com/2015/07/google-interview-questions-2.html
abbre word again... follow up是 word->w2d, 另一个wold->wo1d, 
也就是说不能group起来，每个都是unique的
返回所有可能的abbreviation

vector<string> allAbbre(string s) {

    vector<string> rt;

    if (s.length() == 0) return rt;

    if (s.length() < 3) {

        rt.push_back(s);

        return rt;

    }

     

    for (int i = 0; i < s.length() - 1; i++) {

        string prefix = s.substr(0,i + 1);

        for (int j = s.length() - 1; j > i + 1; j--) {

            string suffix = s.substr(j);

            rt.push_back(prefix + to_string(j - i - 1) + suffix);

        }

    }

     

    return rt;

}