object ZebraPuzzle { trait HousePart sealed trait Color extends HousePart case object Red extends Color case object Green extends Color case object Yellow extends Color case object Blue extends Color case object Ivory extends Color object Color { val values: List[Color] = List(Red, Green, Yellow, Blue, Ivory) } sealed trait Resident extends HousePart case object Englishman extends Resident case object Spaniard extends Resident case object Ukrainian extends Resident case object Norwegian extends Resident case object Japanese extends Resident object Resident { val values: List[Resident] = List(Englishman, Spaniard, Ukrainian, Norwegian, Japanese) } sealed trait Pet extends HousePart case object Dog extends Pet case object Snails extends Pet case object Fox extends Pet case object Horse extends Pet case object Zebra extends Pet object Pet { val values: List[Pet] = List(Dog, Snails, Fox, Horse, Zebra) } sealed trait Beverage extends HousePart case object Coffee extends Beverage case object Tea extends Beverage case object Milk extends Beverage case object OrangeJuice extends Beverage case object Water extends Beverage object Beverage { val values: List[Beverage] = List(Coffee, Tea, Milk, OrangeJuice, Water) } sealed trait Cigarette extends HousePart case object OldGold extends Cigarette case object Kools extends Cigarette case object Chesterfields extends Cigarette case object LuckyStrike extends Cigarette case object Parliaments extends Cigarette object Cigarette { val values: List[Cigarette] = List(OldGold, Kools, Chesterfields, LuckyStrike, Parliaments) } sealed trait Position extends HousePart { def fromEnum: Int } case object One extends Position { override val fromEnum = 0 } case object Two extends Position { override val fromEnum = 1 } case object Three extends Position { override val fromEnum = 2 } case object Four extends Position { override val fromEnum = 3 } case object Five extends Position { override val fromEnum = 4 } object Position { val values: List[Position] = List(One, Two, Three, Four, Five) } case class House(position: Position, color: Color, resident : Resident, beverage: Beverage, cigarette: Cigarette, pet: Pet) { def toTheRight(other: House): Boolean = this.position.fromEnum == other.position.fromEnum + 1 def nextTo(other: House): Boolean = math.abs(this.position.fromEnum - other.position.fromEnum) == 1 } case class Solution(waterDrinker: Resident, zebraOwner: Resident) lazy val solve: Solution = { def residentWith(what: House => HousePart, value: HousePart): Resident = houseWith(what, value, fiveHouses).resident val waterDrinker = residentWith((_.beverage), Water) val zebraOwner = residentWith((_.pet), Zebra) Solution(waterDrinker = waterDrinker, zebraOwner = zebraOwner) } lazy val fiveHouses: List[House] = { def housesAtPosition(position: Position): List[House] = validHouses filter (_.position == position) val candidates = for { one <- housesAtPosition(One) two <- housesAtPosition(Two) if uniqueHouses(List(one, two)) three <- housesAtPosition(Three) if uniqueHouses(List(one, two, three)) four <- housesAtPosition(Four) if uniqueHouses(List(one, two, three, four)) five <- housesAtPosition(Five) if uniqueHouses(List(one, two, three, four, five)) candidates = List(one, two, three, four, five) if validPositions(candidates) } yield candidates candidates.head } private lazy val validHouses: List[House] = for { position <- Position.values color <- Color.values resident <- Resident.values beverage <- Beverage.values cigarette <- Cigarette.values pet <- Pet.values house = House(position, color, resident, beverage, cigarette, pet) if validHouse(house) } yield house def validHouse(house: House): Boolean = { val House(position, color, resident, beverage, cigarette, pet) = house List( (color == Red, resident == Englishman), (resident == Spaniard, pet == Dog), (color == Green, beverage == Coffee), (resident == Ukrainian, beverage == Tea), (cigarette == OldGold, pet == Snails), (color == Yellow, cigarette == Kools), (position == Three, beverage == Milk), (position == One, resident == Norwegian), (beverage == OrangeJuice, cigarette == LuckyStrike), (resident == Japanese, cigarette == Parliaments)) forall (iff _).tupled } private def iff(p1: Boolean, p2: Boolean): Boolean = (p1, p2) match { case (true, true) => true case (false, false) => true case _ => false } private def uniqueHouses(houses: List[House]): Boolean = { def unique(what: House => HousePart): Boolean = (houses map what).distinct.length == houses.length unique (_.color) && unique (_.resident) && unique (_.beverage) && unique (_.cigarette) && unique (_.pet) } private def houseWith(what: House => HousePart, value: HousePart, houses: List[House]): House = houses find (what(_) == value) getOrElse(throw new Exception(s"could not find house with $value")) private def validPositions(houses: List[House]): Boolean = { def _houseWith(what: House => HousePart, value: HousePart): House = houseWith(what, value, houses) (_houseWith(_.color, Green) toTheRight _houseWith(_.color, Ivory)) && (_houseWith(_.cigarette, Chesterfields) nextTo _houseWith(_.pet, Fox)) && (_houseWith(_.cigarette, Kools) nextTo _houseWith(_.pet, Horse)) && (_houseWith(_.resident, Norwegian) nextTo _houseWith(_.color, Blue)) } }