code: public int[] generateClustered(int N, int Max) {
                  int[] array = new int[N];
                  fillClustered(array, 0, N, 0, Max);
                  return array;
          }
docs: generates randomly N distinct integers from 0 to Max.
  
  @param N
  number of integers to generate
  @param Max
  maximal value of the integers
  @return array containing the integers