docs: public void permute(final int[] arr) {
      checkArgument(arr.length == sources.length);
      final int[] tmp = new int[arr.length];
      for (int i = 0; i < tmp.length; ++i) {
        tmp[i] = arr[sources[i]];
      }
      System.arraycopy(tmp, 0, arr, 0, arr.length);
    }