Advent of Code 2023-4.scala

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

case class Card(winningNumbers: Vector[Int], numbers: Vector[Int]):
  def matchCount(): Int =
    winningNumbers.intersect(numbers).size

object Card {
  def apply(line: String): Card =
    val numbers = line.trim.split(" ").map(_.trim).filter(_.nonEmpty).toVector
    val (winningNumbers, normalNumbers) = numbers.splitAt(numbers.indexOf("|"))
    Card(winningNumbers.drop(2).map(_.toInt), normalNumbers.drop(1).map(_.toInt))
}

def solve4_1(cards: Vector[Card]): Int =
  cards.map { card =>
    if (card.matchCount() == 0) 0 else 1 << (card.matchCount() - 1)
  }.sum

def solve4_2(cards: Vector[Card]): Int =
  val cardCounts: Vector[Int] = Vector.fill(cards.length)(1)
  cards.indices.foldLeft(cardCounts) { (acc, idx) =>
    val matchCount = cards(idx).matchCount()
    (1 to matchCount).foldLeft(acc) { (acc, i) =>
      acc.updated(idx + i, acc(idx + i) + acc(idx))
    }
  }.sum

@main def solve4(): Unit =
  val in = new FileInputStream("example4-2.in")
  System.setIn(in)
  val inputs = Iterator.continually(StdIn.readLine())
    .takeWhile(line => null != line)
    .toVector

  val cards = inputs.map(Card.apply)
  println(solve4_1(cards))
  println(solve4_2(cards))