Scalania9.scala

import scala.util.Random

object S99_P23 {
  def removeAt[T](n: Int, ts: Seq[T]) = (ts.take(n) ++ ts.drop(n + 1), ts(n))

  def randomSelect[T](count: Int, ts: Seq[T]): Seq[T] = {
    val r = new Random
    def go(count: Int, ts: Seq[T], acc: Seq[T]): Seq[T] = {
      if (count > 0) {
        val (next, elem) = removeAt(r.nextInt(ts.length), ts)
        go(count - 1, next, elem +: acc)
      } 
      else acc
    }
    go(count, ts, Seq.empty[T])
  }
}