codysjam.scala

import scala.annotation.tailrec

val input = IndexedSeq(9, 9, 12, 12, 12, 15, 16, 20)
def run(input: IndexedSeq[Int]): IndexedSeq[Int] = {
  val result = IndexedSeq.empty[Int]
  go(input: IndexedSeq[Int], result: IndexedSeq[Int])
}
@tailrec
def go(input: IndexedSeq[Int], result: IndexedSeq[Int]): IndexedSeq[Int] = {
  if(input.isEmpty) {
    result
  } else {
    val salePrice = input.head
    val newList = removeRegularPrice(input)
    go(newList, result ++ IndexedSeq(salePrice))
  }
}
def removeRegularPrice(prices: IndexedSeq[Int]) : IndexedSeq[Int] = {
  if(prices.nonEmpty) {
    val salePrice = prices.head
    val regPrice = salePrice * 4 / 3
    val index = prices.indexOf(regPrice)
    val (fst, snd) = prices.splitAt(index)
    fst.tail ++ snd.tail
  } else {
    IndexedSeq.empty[Int]
  }
}
run(input)