TopCoder practice for the 'PhonePad' problem http://community.topcoder.com/stat?c=problem_statement&pm=4464&rd=7219

DialPad.scala

// Code exercise for http://community.topcoder.com/stat?c=problem_statement&pm=4464&rd=7219
object DialPad {
  val dial = Array(Array("1","2","3"),Array("4","5","6"),Array("7","8","9"),Array("*","0","#"))
  // creates a map of a dial key and its coordinates. e.g 1 -> (0,0)
  val dialCoords = for {indexedRow <- (dial.indices zip dial)
        row <- indexedRow._2.indices zip indexedRow._2
        elem <- row._2 } yield (elem -> (indexedRow._1, row._1))
  val dialCoordMap = dialCoords.toMap
  // for each key creates a lookup map to all other keys in the form (dialKey -> map(dialKey -> distance value))
  val dialLookup = dialCoordMap.map({case (key, (x1,y1)) => key -> dialCoordMap.map({case (k2, (x2,y2)) => (k2, math.abs(x2-x1)+math.abs(y2-y1))})})
  // based on the loopup map, looking up a specific transition are two map lookups of O(1)
  def transitionValue(transition:Tuple2[Char,Char]) = transition match {
    	case (from, to) => dialLookup.get(from).get(to)
 	}
 	
  // calculating the  Manhattan distance is now a question of getting all the transitions starting on dialkey-5 and summing them up
  def fingerMovement(phoneNumber:String)  = {
    // finger starts on 5
  	val transitions = 5+phoneNumber zip phoneNumber
  	transitions.foldLeft(0)((x,y) => x + transitionValue(y))
  }
  fingerMovement("911")                           //> res0: Int = 6
  fingerMovement("5555555")                       //> res1: Int = 0
  fingerMovement("8606335540")                    //> res2: Int = 16

}