S99 Problem 3

S99P03.scala

/*
 * S99 Problem 3
 * D Holbrook
 */
object P03 extends App {

  @scala.annotation.tailrec
  def nThRecursive[A](n: Int, l: List[A]): A = (n, l) match {
    case (x , _) if x < 0 => throw new IllegalArgumentException  //should never have negative number
    case (0, hd :: _)     => hd                                  //counter is zero, return head
    case (x, _ :: tail)   => nThRecursive(x - 1, tail)           //counter is non-zero, decrement counter, remove head
    case _                => throw new NoSuchElementException    //should never be reached
  }

  val result = nThRecursive(2, List("A", "B", "C", "D", "E"))
  assert(result == "C")
  println(result)

}