Day 4

aoc/src/Day4.scala

@@ -0,0 +1,74 @@
+import scala.io.Source
+
+object Day4 extends App:
+
+  val input = Source
+    .fromURL(getClass.getResource("day4Input.txt"))
+    .mkString
+
+  final case class Bingo(boards: Array[Board], playedNumbers: Seq[Int]):
+    def playNumber(number: Int) =
+      Bingo(
+        boards.map(board => if (board.isWinner) board else board.mark(number)),
+        playedNumbers.appended(number)
+      )
+
+    def winningBoards: Seq[Board] = boards
+      .filter(_.isWinner)
+      .map(board => (board, board.lastMarked.map(playedNumbers.indexOf(_))))
+      .sortBy(_._2)
+      .map(_._1)
+
+    val gameOver = boards.forall(_.isWinner)
+
+  object Bingo:
+    def parse(input: Array[String]): Bingo =
+      Bingo(input.map(Board.parse), Seq())
+
+  final case class Board(
+      val rows: Array[Array[Cell]],
+      lastMarked: Option[Int] = None
+  ):
+    val isWinner: Boolean = rows.exists(_.forall(_.marked)) ||
+      rows.transpose.exists(_.forall(_.marked))
+
+    def mark(number: Int): Board =
+      Board(
+        rows.map(_.map(_.mark(number))),
+        Some(number)
+      )
+
+    def score: Int =
+      rows.flatMap(_.filterNot(_.marked).map(_.value)).sum *
+        lastMarked.getOrElse(0)
+
+  object Board:
+    def parse(input: String) =
+      Board(
+        input
+          .split('\n')
+          .map(
+            _.split(' ')
+              .filter(_.nonEmpty)
+              .map(Cell.parse)
+          )
+      )
+
+  final case class Cell(value: Int, marked: Boolean = false):
+    def mark(number: Int): Cell =
+      if (number == value) Cell(value, true) else this
+
+  object Cell:
+    def parse(input: String) = Cell(input.toInt)
+
+  val numbersAndBoardsInput = input.split("\n\n")
+  val drawnNumbers = numbersAndBoardsInput.head.split(',').map(_.toInt)
+  val initialState = Bingo.parse(numbersAndBoardsInput.tail)
+
+  val finalState = drawnNumbers.foldLeft(initialState)(_.playNumber(_))
+
+  val firstWinningBoard = finalState.winningBoards.head
+  println(s"Part 1: ${firstWinningBoard.score}")
+
+  val lastWinningBoard = finalState.winningBoards.last
+  println(s"Part 2: ${lastWinningBoard.score}")