S99 P09 http://aperiodic.net/phil/scala/s-99/

S9909.scala

package scalaninetynine

/*
 * S99 P09 http://aperiodic.net/phil/scala/s-99/
 * If a list contains repeated elements they should be placed in separate 
 * sublists.
 * 
 * Example:
 * scala> pack(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
 * res0: List[List[Symbol]] = List(List('a, 'a, 'a, 'a), List('b), List('c, 'c), List('a, 'a), List('d), List('e, 'e, 'e, 'e))
 *
 * D. Holbrook 2012-01-31
 */
object S9909 extends App {

  def pack[A](l: List[A]): List[List[A]] = {
    l.foldLeft(List(List[A]())) {
      case (acc, i) if acc.head == Nil || acc.head.head == i => (i :: acc.head) :: acc.tail
      case (acc, i)                                          => List(i) :: acc
    }.reverse
  }

  val r = pack(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
  assert(r == List(List('a, 'a, 'a, 'a), List('b), List('c, 'c), List('a, 'a), List('d), List('e, 'e, 'e, 'e)))

}