Game of Life

GameOfLife.scala

case class GameOfLife private(width: Int, height: Int, cells: Set[Point]) {

  private def neighbors(p: Point): Set[Point] = {
    (for {
      x <- Math.max(1, p.x - 1).to(Math.min(this.width, p.x + 1))
      y <- Math.max(1, p.y - 1).to(Math.min(this.height,p.y + 1))
    } yield Point(x, y)).toSet - p
  }


  def changeSet: (Set[Point], Set[Point], Set[Point]) = {
    this.cells.map(neighbors)
      .foldLeft(Map.empty[Point, Int]) { case (allNeighbors, neighborSet) =>
        neighborSet.foldLeft(allNeighbors) { case (currentNeighbors, neighbor) =>
          currentNeighbors + (neighbor -> (currentNeighbors.getOrElse(neighbor, 0) + 1))
        }
      }
      .foldLeft((Set.empty[Point], Set.empty[Point], Set.empty[Point])) {
        case (s@(survivors, dying, born), (k, v)) =>
          (this.cells.contains(k), v) match {
            case (true, 2) => (survivors + k, dying, born)
            case (true, 3) => (survivors + k, dying, born)
            case (true, _) => (survivors, dying + k, born)
            case (false, 3) => (survivors, dying, born + k)
            case (false, _) => s
          }
      }
  }

  def tick(): World = {
    val (survivors, _, born) = changeSet
    GameOfLife(this.width, this.height, survivors ++ born)
  }
}

object GameOfLife {
  def seed[A](width: Int, height: Int, points: Set[Point]): World = {
    GameOfLife(width, height, points)
  }
}