Advent of Code 22.scala

import java.io.FileInputStream
import scala.io.StdIn

case class Round(player1: Vector[Int], player2: Vector[Int])
case class Game(round: Round, history: Set[Round]) {
  def player1Win(): Game = {
    Game(Round(round.player1.tail :+ round.player1.head :+ round.player2.head, round.player2.tail), history + round)
  }

  def player2Win(): Game = {
    Game(Round(round.player1.tail, round.player2.tail :+ round.player2.head :+ round.player1.head), history + round)
  }
}

def score(deck: Vector[Int]): Int = {
  deck.zipWithIndex.foldLeft(0) { case (acc, (value, idx)) =>
    acc + (deck.length - idx) * value
  }
}

def solve22_1(player1: Vector[Int], player2: Vector[Int]): Int = {
  if player1.isEmpty then
    score(player2)
  else if player2.isEmpty then
    score(player1)
  else if player1.head > player2.head then
    solve22_1(player1.tail :+ player1.head :+ player2.head, player2.tail)
  else
    solve22_1(player1.tail, player2.tail :+ player2.head :+ player1.head)
}


def winnerDeck(games: Vector[Game]): Vector[Int] = {
  val game = games.last
  val round = game.round
  val player1 = round.player1
  val player2 = round.player2
  if player1.isEmpty then
    games.init.lastOption match
      case Some(lastGame) =>
        winnerDeck(games.init.init :+ lastGame.player2Win())
      case _ =>
        player2
  else if player2.isEmpty || game.history.contains(round) then
    games.init.lastOption match
      case Some(lastGame) =>
        winnerDeck(games.init.init :+ lastGame.player1Win())
      case _ =>
        player1
  else
    if player1.head < player1.length && player2.head < player2.length then
      winnerDeck(games :+ Game(Round(player1.tail.take(player1.head), player2.tail.take(player2.head)), Set()))
    else if player1.head > player2.head then
      winnerDeck(games.init :+ game.player1Win())
    else
      winnerDeck(games.init :+ game.player2Win())
}

def solve22_2(player1: Vector[Int], player2: Vector[Int]): Int = {
  val deck = winnerDeck(Vector(Game(Round(player1, player2), Set())))
  score(deck)
}

def readCardDeck(): Vector[Int] = {
  Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line && line.trim.nonEmpty)
    .toVector
    .tail
    .map(_.toInt)
}

@main def solve22() =
  val in = new FileInputStream("example22-1.in")
  System.setIn(in)

  val player1 = readCardDeck()
  val player2 = readCardDeck()
  println(solve22_1(player1, player2)) // 33434
  println(solve22_2(player1, player2)) // 31657