ReadPhoneNumber.scala

object ReadPhoneNumber extends App {

  def read(numberStr: String, formatStr: String): String = {

    val (numbers, format) = (numberStr map (_ - '0'), formatStr split '-' map (_.toInt))

    val segments: Seq[Seq[Int]] = ((List.empty[Seq[Int]], numbers) /: format) {
      case ((acc, numbers), count) => val (h, t) = numbers splitAt count; (h :: acc, t)
    }._1.reverse

    def runLength: Seq[Int] => Seq[(Int, Int)] = _.foldRight(List.empty[(Int, Int)]) {
      case (digit, (d, r) :: accTail) if digit == d => (d, r + 1) :: accTail
      case (digit, acc) => (digit, 1) :: acc
    }

    segments flatMap runLength flatMap {
      case (d, r) =>
        val digitStr = ("zero one two three four five six seven eight nine" split ' ')(d)
        if (2 <= r && r <= 10)
          Seq(("double triple quadruple quintuple sextuple septuple octuple nonuple decuple"
            split ' ')(r - 2), digitStr)
        else
          Seq.fill(r)(digitStr)
    } mkString " "
  }

  def process(lineIn: Iterator[String])(lineOut: String => Unit) =
    for (i <- 1 to lineIn.next().toInt) {
      val Array(n, f) = lineIn.next() split ' '
      lineOut(s"Case #$i: ${read(n, f)}")
    }

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

}