p16.scala

object S99_P16 {
  def drop[T](n: Int, ts: Seq[T]): Seq[T] = {
    var iter = 0;
    def op(el: T): Boolean = { iter = iter + 1; (iter % n != 0) }
    ts filter op
  }

  def drop[T](n: Int, ts: Seq[T]): Seq[T] = 
    for (e <- ts.zipWithIndex if (e._2 + 1) % n != 0) yield e._1

  def drop[T](n: Int, ts: Seq[T]): Seq[T] = {
    def everyN(e: (T, Int)): Boolean = ((e._2 + 1) % n) != 0
    ts.zipWithIndex.filter(everyN).map(_._1)
  }

  def drop[T](n: Int, ts: Seq[T]): Seq[T] =
    ts.grouped(n).flatMap(_.take(n - 1)).toList
}