gistfile1.txt

/*
 * Copyright 2011-2012 Typesafe Inc.
 *
 * This work is based on the original contribution of WeigleWilczek.
 *
 * Unless otherwise agreed, training materials may only be used for
 * educational and reference purposes by individual named participants
 * in a training course offered by Typesafe or a Typesafe training partner.
 * Unauthorized reproduction, redistribution, or use of this material is prohibited.
 */

package misc

class PhoneMnemonics(words: Set[String]) {

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

  /**
   * Inverse of the mnemonics map, e.g. 'A' -> '2', 'B' -> '2'.
   */
  val charCode: Map[Char, Char] =
    for {
      digitAndString <- mnemonics
      letter <- digitAndString._2
    } yield letter -> digitAndString._1 

  /**
   * Maps a word to its digit representation, e.g. "Java" -> "5282".
   */
  def wordCode(word: String): String = word.toUpperCase map charCode

  /**
   * Groups all words by their number representations, e.g. "5282" -> Set("Java", "Kata", ...).
   */
  val wordsForNumber: Map[String, Set[String]] = words groupBy wordCode
    /*
    Map() ++ (for {
      word <- words
      code = wordCode(word)
    } yield (code, words.filter(w => wordCode(w) == code)))
*/    
  /**
   * All ways to encode a number as a pharse, i.e. as a sequence of words.
   */
  def encode(number: String): Set[Seq[String]] =
    if (number.length() == 0) Set(Seq())
    else for {
      splitPoint <- Set() ++ (1 to number.length)
      firstWordDigits = number take splitPoint
      phrase <- encode(number drop splitPoint)
      word <- wordsForNumber.getOrElse(firstWordDigits, Set())
    } yield word +: phrase

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