[LeetCode] Unique Word Abbreviation

Problem Description:

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 

To check for unique abbreviation, we maintain a mapping from a specific abbreviation to all words which have the abbreviation. Then we just need to check no other words have the same abbreviation as the given word.

The code is as follows.

class ValidWordAbbr {
public:
    ValidWordAbbr(vector<string> &dictionary) {
        for (string& d : dictionary) {
            int n = d.length();
            string abbr = d[0] + to_string(n) + d[n - 1];
            mp[abbr].insert(d);
        }
    }

    bool isUnique(string word) {
        int n = word.length();
        string abbr = word[0] + to_string(n) + word[n - 1];
        return mp[abbr].count(word) == mp[abbr].size(); 
    }
private:
    unordered_map<string, unordered_set<string>> mp;
};


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