card-game.swift

import Darwin

extension Array {
  func shuffle() -> Array {
    // this will sometimes crash (submitted bug #17127524)
    self.sort { _,_ in arc4random_uniform(2) == 1 }
    return self
  }
  mutating func removeAtIndexes( indexes:Int... ) {
    indexes.sort(>)
    for i in indexes { removeAtIndex(i) }
  }
}

class CardSet {
  struct Card {
    enum Suit:Int {
      case Hearts, Diamonds, Clubs, Spades
    }
    enum Rank:Int {
      case Two, Three, Four, Five, Six
      case Seven, Eight, Nine, Ten
      case Jack, Queen, King, Ace
    }

    let suit:Suit
    let rank:Rank
  }

  var cards:Card[]

  init() { cards = [] }
  init( _ cards:Card[] ) { self.cards = cards }

  var isEmpty:Bool { return cards.isEmpty }
}

class Deck:CardSet {
  init() {
    let indexes = Array(0..52).shuffle()
    super.init(indexes.map { index in
      let suit = Card.Suit.fromRaw(index % 4)!
      let rank = Card.Rank.fromRaw(index % 13)!
      return Card(suit: suit, rank: rank)
    })
  }

  func drawCard() -> Card { return cards.removeLast() }
}

class Hand:CardSet {
  var canPlay:Bool {
    return cards.count >= 4 && (ranksMatch() || suitsMatch())
  }

  func play() {
    if ranksMatch() { cards.removeAtIndexes(3, 2, 1, 0) }
    else if suitsMatch() { cards.removeAtIndexes(2, 1) }
  }

  func add( card:Card ) { cards.insert(card, atIndex: 0) }

  func ranksMatch() -> Bool { return cards[0].rank == cards[3].rank }
  func suitsMatch() -> Bool { return cards[1].suit == cards[2].suit }
}

struct Game {
  var deck = Deck()
  var hand = Hand()

  func play() -> Bool {
    while !deck.isEmpty {
      hand.add( deck.drawCard() )
      while hand.canPlay { hand.play() }
    }
    return hand.isEmpty
  }
}

let games = 1000
var wins = 0
for _ in 0..games { if Game().play() { wins++ } }

let winningPercentage = Double(wins) / Double(games)
println("Played \(games) games, \(wins) (\(winningPercentage)%) wins.")

'Card Game' in Swift

I don't know what this card game is called. I often use it when fiddling with a new language. The rules are:

• use a full standard deck
• if you ever have less than 4 cards, draw cards until you have at least 4
• look at the first (newest) 4 cards in your hand
  • if the two cards on the outside have the same value (king, 2, 6, etc) -> remove all 4
  • if the two cards on the inside have the same suit -> remove the 2 middle cards
  • if nothing matches, draw another card
• if the deck is empty and you have 0 cards in your hand, you win

When you play it by hand you effectively never win, so I have written several of these for various languages (Python, Ruby, JavaScript, Erlang, Go, Clojure, to name a few) and have pretty much settled on an approximate 0.002% chance of winning.

To run this you need Xcode 6 (atm in beta), start a new Command-Line OSX app and paste this code into main.swift.