S99 P08 http://aperiodic.net/phil/scala/s-99/

S9908.scala

package scalaninetynine
/*
 * S99 P08 http://aperiodic.net/phil/scala/s-99/
 * 
 * If a list contains repeated elements they should be replaced with a 
 * single copy of the element. The order of the elements should not be changed.
 * 
 * Example:
 * scala> compress(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
 * res0: List[Symbol] = List('a, 'b, 'c, 'a, 'd, 'e)
 *     
 * D. Holbrook 2012-01-28
 */
object S9908 extends App {

  val l = List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e)

  def compress[A](l: List[A]): List[A] = {
    l.foldLeft(List[A]()) {
      case (acc, s) if acc == Nil || acc.head != s => s :: acc
      case (acc, _)                                => acc
    }.reverse
  }

  val cl = compress(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
  assert(cl == List('a, 'b, 'c, 'a, 'd, 'e))

}