Coder.scala

import collection.mutable.HashMap

class Coder(words: List[String]) {

  (2 -> "ABC",  new ArrowAssoc('3') -> "DEF")

  private val mnemonics = Map(
      '2' -> "ABC", '3' -> "DEF", '4' -> "GHI", '5' -> "JKL",
      '6' -> "MNO", '7' -> "PQRS", '8' -> "TUV", '9' -> "WXYZ")


  ('1', "1") match {
    case (digit, str) => true
    case _ => false
  }

  /** Invert the mnemonics map to give a map from chars 'A' ... 'Z' to '2' ... '9' */
  private val charCode0: Map[Char, Char] = mnemonics withFilter {
    case (digit, str) => true
    case _ => false
  } flatMap { x$1 =>
    x$1 match {
      case (digit, str) => str map (ltr => ltr -> digit)
    }
  }

  private val charCode: Map[Char, Char] =
    for ((digit, str) <- mnemonics; ltr <- str) yield ltr -> digit

    /** Maps a word to the digit string it can represent */
  private def wordCode(word: String): String = word map charCode

  /** A map from digit strings to the words that represent them */
  private val wordsForNum: Map[String, List[String]] =
    words groupBy wordCode withDefaultValue Nil

  /** All ways to encode a number as a list of words */
  def encode(number: String): Set[List[String]] =
    if (number.isEmpty) Set(Nil)
    else {
      for {
        splitPoint <- 1 to number.length
        word <- wordsForNum(number take splitPoint)
        rest <- encode(number drop splitPoint)
      } yield word :: rest
    }.toSet

  /** Maps a number to a list of all word phrases that can represent it */
  def translate(number: String): Set[String] = encode(number) map (_ mkString " ")

}

object Coder {
  def main(args : Array[String]) : Unit = {
    val coder = new Coder(List("Scala", "sobls", "Python", "Ruby", "C", "A", "rocks", "sucks", "works", "Racka"))
//    println(coder.wordsForNum)
    println(coder.translate("7225276257"))
  }
}