Day 22

day22/main.swift

@@ -0,0 +1,87 @@
+import Foundation
+let data = loadData(day: 22)
+let scanner = Scanner(string: data)
+
+
+guard scanner.string("Player 1:") else { fatalError() }
+let p1 = scanner.integers()
+var player1Deck = p1
+
+guard scanner.string("Player 2:") else { fatalError() }
+let p2 = scanner.integers()
+var player2Deck = p2
+
+assert(player1Deck.count == player2Deck.count)
+
+while !player1Deck.isEmpty && !player2Deck.isEmpty {
+    let a = player1Deck.removeFirst()
+    let b = player2Deck.removeFirst()
+
+    if a > b {
+        player1Deck.append(contentsOf: [a, b])
+    } else {
+        player2Deck.append(contentsOf: [b, a])
+    }
+}
+
+func calculateScore(_ deck: [Int]) -> Int {
+    deck.reversed().enumerated().reduce(0) { $0 + $1.element * ($1.offset + 1) }
+}
+
+if player2Deck.isEmpty {
+    print("Player 1 wins", calculateScore(player1Deck))
+} else {
+    print("Player 2 wins", calculateScore(player2Deck))
+}
+
+struct PlayedDeck: Hashable {
+    let player1: [Int]
+    let player2: [Int]
+}
+var playedDecks: Set<PlayedDeck> = []
+
+
+func playGame(deck1: [Int], deck2: [Int])  -> (winner: Bool, score: Int) {
+    var deck1 = deck1
+    var deck2 = deck2
+    var playedDecks: Set<PlayedDeck> = []
+
+    while !deck1.isEmpty && !deck2.isEmpty {
+        if !playedDecks.insert(PlayedDeck(player1: deck1, player2: deck2)).inserted {
+            return (true, calculateScore(deck1))
+        }
+        playRound(deck1: &deck1, deck2: &deck2)
+    }
+
+    let winner = deck2.isEmpty
+    return (winner, winner ? calculateScore(deck1) : calculateScore(deck2))
+}
+
+func playRound(deck1: inout [Int], deck2: inout [Int]) {
+    let a = deck1.removeFirst()
+    let b = deck2.removeFirst()
+
+    let winner: Bool
+    if a <= deck1.count && b <= deck2.count {
+        winner = playGame(deck1: Array(deck1[0..<a]), deck2: Array(deck2[0..<b])).winner
+    } else {
+        winner = a > b
+    }
+
+    if winner {
+        deck1.append(contentsOf: [a, b])
+    } else {
+        deck2.append(contentsOf: [b, a])
+    }
+}
+
+
+player1Deck = p1
+player2Deck = p2
+
+    let (winner, score) = playGame(deck1: p1, deck2: p2)
+    if winner {
+        print("Player 1 wins", score)
+    } else {
+        print("Player 2 wins", score)
+    }