CodyJams.scala

 object CodyJams extends App {

   def salePrices(prices: Seq[Int]): Seq[Int] = 
     ((List.empty[Int], collection.immutable.Queue.empty[Int]) /: prices) {
       case ((acc, originals), price) if originals.headOption == Some(price) =>
         (acc, originals.tail)
       case ((acc, originals), price) =>
         (price::acc, originals :+ (price / 3 * 4))
     }._1.reverse

  def process(lineIn: Iterator[String])(lineOut: String => Unit) =
    for (i <- 1 to lineIn.next().toInt) {
      val n = lineIn.next().toInt
      val prices = lineIn.next().split(' ').map(_.toInt)
      lineOut(s"Case #$i: ${salePrices(prices) mkString " "}")
    }

  val filename = "A-large-practice"
  val writer = new java.io.PrintWriter(filename + ".out")
  try {
    process(io.Source.fromFile(filename + ".in").getLines) { s =>
      writer.println(s); writer.flush()
    }
  } finally {
    writer.flush(); writer.close()
  }
}

CodyJamsTest.scala

import org.scalatest._

import CodyJams._

class CodyJamsTest extends FunSuite with Matchers {

  test("sample #1") {
    assert(salePrices(Seq(15, 20, 60, 75, 80, 100)) === Seq(15, 60, 75))
  }

  test("sample #2") {
    assert(salePrices(Seq(9, 9, 12, 12, 12, 15, 16, 20)) === Seq(9, 9, 12, 15))
  }

  test("small #6") {
    assert(
      salePrices(
        Seq(270624780, 336144033, 360833040, 448192044, 736130808, 745857189, 981507744, 994476252)) ===
        Seq(270624780, 336144033, 736130808, 745857189))
  }

  test("sample case") {
    val input = """2
3
15 20 60 75 80 100
4
9 9 12 12 12 15 16 20""".lines

    val expected = """Case #1: 15 60 75
Case #2: 9 9 12 15""".lines

    lineComparison(input, expected)
  }

  test("full small case") {
    val input = io.Source.fromFile("A-small-practice.in").getLines()
    val expected = io.Source.fromFile("A-small-practice.out").getLines()

    lineComparison(input, expected)
  }

  test("full large case") {
    val input = io.Source.fromFile("A-large-practice.in").getLines()
    val expected = io.Source.fromFile("A-large-practice.out").getLines()

    lineComparison(input, expected)
  }

  def lineComparison(input: Iterator[String], expected: Iterator[String]): Unit = {
    process(input) { s =>
      for (line <- s.lines) assert(line.trim === expected.next().trim)
    }
    assert(expected.hasNext === false, "Finished too fast.")
  }

}