Reverse or Rotate

object RevRot {

  def revRot(strng: String, sz: Int): String = {
    def isDivisible(s: String): Boolean = s.map[Int](x => x.toInt).map(x => x * x * x).sum % 2 == 0

    def rotate(s: String): String = s.drop(1) + s.head

    if (sz > strng.length || sz <= 0 || strng.length == 0) ""
    else strng.grouped(sz).filter(_.length == sz).map(x => if (isDivisible(x)) x.reverse else rotate(x)).mkString
  }
}