Day 7

Day7.scala

@@ -0,0 +1,92 @@
+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 ranks = deck.sorted.toArray
+    if ranks(0) == ranks(4) then Five
+    else if ranks(0) == ranks(3) || ranks(1) == ranks(4) then Four
+    else if ranks(0) == ranks(2) && ranks(3) == ranks(4) || ranks(0) == ranks(
+        1
+      ) && ranks(2) == ranks(4)
+    then House
+    else if ranks(0) == ranks(1) && ranks(2) == ranks(3) || ranks(0) == ranks(
+        1
+      ) && ranks(3) == ranks(4) || ranks(1) == ranks(2) && ranks(3) == ranks(4)
+    then Pairs
+    else
+      lazy val three = (0 until ranks.length - 2)
+        .find(i => ranks(i) == ranks(i + 2))
+        .map(i => Three)
+      lazy val pair = (0 until ranks.length - 1)
+        .find(i => ranks(i) == ranks(i + 1))
+        .map(i => Pair)
+      three.orElse(pair).getOrElse(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 =
+    deck.iterator
+      .foldLeft(Iterator("")) { (it, chr) =>
+        if chr == 'J' then it.flatMap(s => possibleCards.map(s + _))
+        else it.map(_ + chr)
+      }
+      .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