Nice work. I'm in the process of learning Scala, a...

2009-03-05T03:09:00.000-03:00

Nice work. I'm in the process of learning Scala, and I've always found it helpful to look at other people's code, pick up some tricks from them and add my own five cents. So here's my take:

object ToyStory {
  case class Toy(name: String, time: Int) {
    override def toString = name
  }

  abstract class Direction
  case object Left extends Direction
  case object Right extends Direction

  case class Move(direction: Direction, toys: List[Toy]) {
    def cost = Iterable.max(toys.map(_.time))

    override def toString =
      toys.mkString("", " and ", "") +
      (if (toys.size == 1) " moves " else " move ") +
      direction.toString.toLowerCase
  }

  type Path = List[Move]

  def pairs[A](s: List[A]) =
    for ((first, index) <- s.toStream.zipWithIndex; second <- s.drop(index + 1))
      yield List(first, second)

  def solutions(toys: List[Toy], limit: Int) = {
    def solve_right(on_left: List[Toy],
                    on_right: List[Toy], limit: Int) : Stream[Path] =
      for (pair <- pairs(on_left);
           move = Move(Right, pair);
           remaining = limit - move.cost if remaining >= 0;
           path <- solve_left(on_left -- pair, pair ::: on_right, remaining))
        yield move :: path

    def solve_left(on_left: List[Toy],
                   on_right: List[Toy], limit: Int) : Stream[Path] =
      on_left match {
        case Nil => Stream(Nil)
        case _ =>
          for (toy  <- on_right.toStream;
               move = Move(Left, List(toy));
               remaining = limit - move.cost if remaining >= 0;
               path <- solve_right(toy :: on_left, on_right - toy, remaining))
            yield move :: path
      }

    solve_right(toys, Nil, limit)
  }

  val toys =
    List(Toy("Buzz", 5), Toy("Woody", 10), Toy("Rex", 20), Toy("Hamm", 25))

  def main(args : Array[String]) : Unit =
    for (path <- solutions(toys, 60))
      println("Solution: " + path.mkString("", ", ", "."))
}

Comments on Jonhnny Weslley / My blog: Escape from Zurg

Nice work. I'm in the process of learning Scala, a...