docs: public static int[] commonElements(int[] arra, int[] arrb) {
  
          int[] c = null;
          int   n = countCommonElements(arra, arrb);
  
          if (n > 0) {
              c = new int[n];
  
              int k = 0;
  
              for (int i = 0; i < arra.length; i++) {
                  for (int j = 0; j < arrb.length; j++) {
                      if (arra[i] == arrb[j]) {
                          c[k++] = arra[i];
                      }
                  }
              }
          }
  
          return c;
      }