Solution to TopCoder problem 'WordCompositionGame' http://community.topcoder.com/stat?c=problem_statement&pm=4483&rd=7228 #ScalaPractice

WorldCompositionGame.scala

object WordCompositionGame {
  def score(listA:Array[String] , listB:Array[String], listC:Array[String]): String = {
    // turn those arrays into some useful Sets
    val a = listA.toSet
    val b = listB.toSet
    val c = listC.toSet
    val all = Set(a,b,c)
	  
    // calculates the intersection of a,b and c
    val abc = all.reduceLeft(_.intersect(_))
	  
    // calculates the score for a set, given all the sets and
    // the common elements (that's an optimization as we only need to calculate that once)
    def scoreSet(set:Set[String],allSets:Set[Set[String]], common:Set[String]):Int = {
      val targetSet = allSets - set
      val score2Sets = (for {set1 <- targetSet} yield (set.diff(common)).intersect(set1))
      val score2 = score2Sets.foldLeft(0)((count,set) => count + set.size)
      val score3 = (set diff targetSet.reduce(_.union(_))).size
      common.size + score2 *2 + score3 * 3
    }
    
    // A map of a set is a set and will eliminate duplicates. As we want every score, we first turn the set into a list
    all.toList.map(x=> scoreSet(x,all,abc)).mkString("/")
  }
  
  val a = Array( "cat", "dog", "pig", "mouse" )   
  val b = Array( "cat", "pig" )                   
  val c = Array( "dog", "cat" )                   
  
  score(a, b, c)                                  //> res0: String = 8/3/3
}