docs: public static int[] randomPermutation(final int[] out, Random random) {
      for(int i = out.length - 1; i > 0; i--) {
        // Swap with random preceeding element.
        int ri = random.nextInt(i + 1);
        int tmp = out[ri];
        out[ri] = out[i];
        out[i] = tmp;
      }
      return out;
    }