code: static int[] moveToBack(int[] neighbors, int v) {
          int j = 0;
          for (int i = 0; i < neighbors.length; i++) {
              if (neighbors[i] != v) {
                  neighbors[j++] = neighbors[i];
              }
          }
          neighbors[neighbors.length - 1] = v;
          return neighbors;
      }
docs: Utility method for shifting a specified value in an index to the back
  (see {@link #permutation(int[])}).
  
  @param neighbors list of neighbors
  @param v         the value to shift to the back
  @return <i>neighbors</i> array