Unique Word Abbreviation

An abbreviation of a word follows the form <first letter><number><last letter>. Below are some examples of word abbreviations:

a) it                      --> it    (no abbreviation)

     1
b) d|o|g                   --> d1g

              1    1  1
     1---5----0----5--8
c) i|nternationalizatio|n  --> i18n

              1
     1---5----0
d) l|ocalizatio|n          --> l10n

Assume you have a dictionary and given a word, find whether its abbreviation is unique in the dictionary. A word’s abbreviation is unique if no other word from the dictionary has the same abbreviation.

Example:

Given dictionary = [ "deer", "door", "cake", "card" ]

isUnique("dear") -> false
isUnique("cart") -> true
isUnique("cane") -> false
isUnique("make") -> true

Store the abbreviations in a hash map. key is abbreviation, value is a vector which contains all the original words whose abbreviation is the key.

//1. does dictionary contains duplicates? NO
//2. can input word is not contained in the dictionary? YES, YOU SHOULD RETURN TRUE
class ValidWordAbbr {
public:
    unordered_map<string, vector<string> > map;
    ValidWordAbbr(vector<string> &dictionary) {
        map.clear();
        for(size_t i = 0; i < dictionary.size(); i++){
            string s = dictionary[i];
            string abbr = buildAbbr(s);
            // abbr is available now
            if(map.find(abbr) == map.end()){
                vector<string> vs;
                vs.push_back(s);
                map[abbr] = vs;
            }
            else{
                map[abbr].push_back(s);
            }
        }
    }

    string buildAbbr(string s){
        string abbr;
        if(s.size() <= 2){
            abbr = s;
        }
        else{
            int len = s.size() - 2;
            abbr.push_back(s[0]);
            abbr.append(to_string(len));
            abbr.push_back(s[s.size() - 1]);
        }
        return abbr;
    }
    bool isUnique(string word) {
        string abbr = buildAbbr(word);
        if(map.find(abbr) == map.end()){
            return true;
        }
        else if(map[abbr].size() == 1 && map[abbr][0] == word){
            return true;
        }
        else{
            return false;
        }
    }
};


// Your ValidWordAbbr object will be instantiated and called as such:
// ValidWordAbbr vwa(dictionary);
// vwa.isUnique("hello");
// vwa.isUnique("anotherWord");