LeetCode-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

Solution:

public class ValidWordAbbr {
    Map<String, String> abbrMap;

    public ValidWordAbbr(String[] dictionary) {
        abbrMap = new HashMap<String, String>();

        for (String word : dictionary) {
            String abbr = getAbbr(word);
            // the abbr is invalid, if it exsits and the corresponding word is not current word.
            if (abbrMap.containsKey(abbr) && !abbrMap.get(abbr).equals(word)) {
                abbrMap.put(abbr, "");
            } else {
                abbrMap.put(abbr, word);
            }
        }
    }

    public boolean isUnique(String word) {
        String abbr = getAbbr(word);
        // true, if @abbr does not exsit or the corresponding word is the @word.
        return (!abbrMap.containsKey(abbr)) || (abbrMap.containsKey(abbr) && abbrMap.get(abbr).equals(word));
    }

    public String getAbbr(String word){
    if (word.length()<=2) return word;

    StringBuilder builder = new StringBuilder();
    builder.append(word.charAt(0));
    builder.append(word.length()-2);
    builder.append(word.charAt(word.length()-1));

    return builder.toString();
    }
}

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