S99_14.scala

object S99_P14 {
  def duplicate[T](as: Seq[T]): Seq[T] = as.flatMap(el => Seq.fill(2)(el))
}

object S99_P14 {
  def duplicate[T](as: Seq[T]): Seq[T] = {
    val reversed = as.foldLeft[Seq[T]](Nil) {
      (acc, el) => el +: (el +: acc)
    }
    reversed.reverse
  }
}

object S99_P14 {
  def duplicate[T](as: Seq[T]): Seq[T] = {
    val reversed = as.foldLeft[Seq[T]](Nil) {
      (acc, el) => Seq.fill(2)(el) ++ acc
    }
    reversed.reverse
  }
}