// P10 (*) Run-length encoding of a list.
//     Use the result of problem P09 to implement the so-called run-length
//     encoding data compression method.  Consecutive duplicates of elements are
//     encoded as tuples (N, E) where N is the number of duplicates of the
//     element E.
//
//     Example:
//     scala> encode(List('a, 'a, 'a, 'a, 'b, 'c, 'c, 'a, 'a, 'd, 'e, 'e, 'e, 'e))
//     res0: List[(Int, Symbol)] = List((4,'a), (1,'b), (2,'c), (2,'a), (1,'d), (4,'e))

object P10 {
  import P09.pack
  def encode[A](ls: List[A]): List[(Int, A)] =
    pack(ls) map { e => (e.length, e.head) }
}