Share my Java solution

  • 9

    The idea is pretty straightforward, we use a map to track a set of words that have the same abbreviation. The word is unique when its abbreviation does not exist in the map or it's the only one in the set.

    public class ValidWordAbbr {
      Map<String, Set<String>> map = new HashMap<>();
      public ValidWordAbbr(String[] dictionary) {
        // build the hashmap
        // the key is the abbreviation
        // the value is a hash set of the words that have the same abbreviation
        for (int i = 0; i < dictionary.length; i++) {
          String a = abbr(dictionary[i]);
          Set<String> set = map.containsKey(a) ? map.get(a) : new HashSet<>();
          map.put(a, set);
      public boolean isUnique(String word) {
        String a = abbr(word);
        // it's unique when the abbreviation does not exist in the map or
        // it's the only word in the set
        return !map.containsKey(a) || (map.get(a).contains(word) && map.get(a).size() == 1);
      String abbr(String s) {
        if (s.length() < 3) return s;
        return s.substring(0, 1) + String.valueOf(s.length() - 2) + s.substring(s.length() - 1);

  • 1

    I think we don't need to contain a set in HashMap, since if we got more than one value corresponds to this key, then this key is just a marker of duplicates. So my suggestion is to replace the value in HashMap by string.

    For duplicates, the value would be some special strings like empty string or null.
    For others, the value is simply the word that produces this key

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