code: public class RangeExtraction {
  
      public static void main(String[] args) {
          int[] arr = {0, 1, 2, 4, 6, 7, 8, 11, 12, 14,
              15, 16, 17, 18, 19, 20, 21, 22, 23, 24,
              25, 27, 28, 29, 30, 31, 32, 33, 35, 36,
              37, 38, 39};
  
          int len = arr.length;
          int idx = 0, idx2 = 0;
          while (idx < len) {
              while (++idx2 < len && arr[idx2] - arr[idx2 - 1] == 1);
              if (idx2 - idx > 2) {
                  System.out.printf("%s-%s,", arr[idx], arr[idx2 - 1]);
                  idx = idx2;
              } else {
                  for (; idx < idx2; idx++)
                      System.out.printf("%s,", arr[idx]);
              }
          }
      }
  }
  