aoc2023/Day7.scala

package aoc.day7

import aoc._

val possibleCards = "AKQJT98765432".reverse

enum DeckKind:
  case High
  case Pair
  case Pairs
  case Three
  case House
  case Four
  case Five

object DeckKind:
  def apply(deck: String) =
    val counts =
      deck.iterator.toSeq.groupBy(identity).values.map(_.length).toSeq
    if counts.contains(5) then Five
    else if counts.contains(4) then Four
    else if counts.contains(3) then if counts.contains(2) then House else Three
    else if counts.count(_ == 2) == 2 then Pairs
    else if counts.contains(2) then Pair
    else High

import DeckKind._

case class Hand(deck: String, bet: Int):
  def deckRank(using cardToRank: Map[Char, Int]) = deck.map(cardToRank(_))
  val kind = DeckKind(deck)

  lazy val bestKind =
    possibleCards
      .map(c => deck.replace('J', c))
      .map(DeckKind(_))
      .maxBy(_.ordinal)

inline def nonZero(ins: Int*) = ins.find(_ != 0).getOrElse(0)

object Parser extends CommonParser:
  val deck = (s"[${possibleCards}]{5}").r
  val hand = deck ~ num ^^ { case (deck ~ num) => Hand(deck, num) }
  def apply(s: String) =
    parse(hand, s).get

// part 1

def handOrdering(toKind: Hand => DeckKind)(using cardOrdering: Map[Char, Int]) =
  new Ordering[Hand]:
    override def compare(dx: Hand, dy: Hand): Int =
      val (x, y) = (toKind(dx), toKind(dy))
      if x.ordinal != y.ordinal then x.ordinal.compareTo(y.ordinal)
      else nonZero(dx.deckRank.zip(dy.deckRank).map(_ compareTo _)*)

def print(using Ordering[Hand]) =
  val hands = lines.map(Parser(_)).toSeq
  val res =
    hands.sorted.zipWithIndex
      .map((h, idx) => h.bet * (idx + 1L))
      .sum
  println(res)

def part1 =
  val ordering = possibleCards.zipWithIndex.toMap
  val handOrd = handOrdering(_.kind)(using ordering)
  print(using handOrd)

// part 2

def part2 =
  val ordering = "J23456789TQKA".zipWithIndex.toMap
  val handOrd = handOrdering(_.bestKind)(using ordering)
  print(using handOrd)

@main def Day7(part: Int) = part match
  case 1 => part1
  case 2 => part2