class CombinationSet {

  public int nbOfCombinations(int k) {
    if (k > set.size())
      return 0;
    if (k == set.size())
      return 1;
    long numerator = factorial(set.size());
    long den1 = factorial(k);
    long den2 = factorial(set.size() - k);
    return (int) (numerator / (den1 * den2));
  }

  public  CombinationSet(Set<? extends Object> set);

}