22th December solution - Advent of Code 2020 - swift

december22_1.swift

while player1Cards.count != 0 && player2Cards.count != 0 {

    let card1 = player1Cards.removeFirst()
    let card2 = player2Cards.removeFirst()
    if card1 > card2 {
        player1Cards.append(contentsOf: [card1, card2])
    } else {
        player2Cards.append(contentsOf: [card2, card1])
    }
}

var winningCards = [Int]()
if player1Cards.count != 0 {
    winningCards = player1Cards
} else {
    winningCards = player2Cards
}

let score = (winningCards.reversed() as [Int]).enumerated().reduce(0) { (score, element) -> Int in
    score + (element.offset + 1) * element.element
}

print(score)

december22_2.swift

var (playerlayer1Winner, winningCards) = playGameWith(player1Cards: player1Cards, player2Cards: player2Cards)
let score = (winningCards.reversed() as [Int]).enumerated().reduce(0) { (score, element) -> Int in
    score + (element.offset + 1) * element.element
}
print(winningCards)
print(score)

func playRoundWith( player1Cards: [Int], player2Cards: [Int], previousRounds: [([Int], [Int])]) -> (Bool, Bool) {
    if previousRounds.contains(where: { (pair) -> Bool in
        pair.0 == player1Cards && pair.1 == player2Cards
    }) {
        return (true, true)
    }
    let card1 = player1Cards.first!
    let card2 = player2Cards.first!
    let deckCount1 = player1Cards.count - 1
    let deckCount2 = player2Cards.count - 1
    if deckCount1 >= card1 && deckCount2 >= card2 {
        let (isPlayer1Winner, _) = playGameWith(player1Cards: player1Cards.dropFirst().dropLast(deckCount1 - card1), player2Cards: player2Cards.dropFirst().dropLast(deckCount2 - card2))
        return (isPlayer1Winner, false)
    } else if card1 > card2 {
        return (true, false)
    } else {
        return (false, false)
    }
}

func playGameWith( player1Cards: [Int], player2Cards: [Int]) -> (Bool, [Int]) {
    var perviousRounds = [([Int], [Int])]()
    var newPlayer1Cards = player1Cards
    var newPlayer2Cards = player2Cards
    while newPlayer1Cards.count != 0 && newPlayer2Cards.count != 0 {
        let (player1WonRound, player1WonGame) = playRoundWith(player1Cards: newPlayer1Cards, player2Cards: newPlayer2Cards, previousRounds: perviousRounds)
        if player1WonGame {
            return (true, newPlayer1Cards)
        }
        perviousRounds.append((newPlayer1Cards, newPlayer2Cards))
        let card1 = newPlayer1Cards.removeFirst()
        let card2 = newPlayer2Cards.removeFirst()
        if player1WonRound {
            newPlayer1Cards.append(contentsOf: [card1, card2])
        } else {
            newPlayer2Cards.append(contentsOf: [card2, card1])
        }
    }
    var winningCards = [Int]()
    if newPlayer1Cards.count != 0 {
        winningCards = newPlayer1Cards
    } else {
        winningCards = newPlayer2Cards
    }
    return (newPlayer1Cards.count != 0, winningCards)
}

december22_shared.swift

import Foundation

let filename = "/Users/felix/xCodeProjects/AdventOfCode2020.playground/Resources/december22.txt"
let contents = try! String(contentsOfFile: filename)
let lines = contents.components(separatedBy: CharacterSet.newlines).filter { !$0.isEmpty}

var player1Cards = [Int]()
var player2Cards = [Int]()

var player1 = true
for line in lines {
    if line.contains("Player 1") {
        player1 = true
    } else if line.contains("Player 2") {
        player1 = false
    } else {
        if player1 {
            player1Cards.append(Int(line)!)
        } else {
            player2Cards.append(Int(line)!)
        }
    }
}