Day 14

src/day14.scala

@@ -0,0 +1,123 @@
+package aoc
+package day14
+
+import scala.annotation.tailrec
+import scala.collection.mutable
+
+val dayNumber = "14"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+def part1(input: String): String =
+  val lines = input.split('\n')
+  val border = lines.head.map(_ => '#').mkString + "##"
+  val grid = lines
+    .map(l => s"#$l#")
+    .prepended(border)
+    .appended(border)
+    .map(_.to(mutable.ArraySeq))
+  for
+    y <- grid.indices
+    x <- grid.head.indices
+  do
+    if grid(y)(x) != 'O' then ()
+    else
+      (y - 1 to (0, -1))
+        .takeWhile(grid(_)(x) == '.')
+        .lastOption
+        .foreach(newY =>
+          grid(y)(x) = '.'
+          grid(newY)(x) = 'O'
+        )
+
+  grid
+    .map(_.count(_ == 'O'))
+    .reverse
+    .zipWithIndex
+    .map((count, row) => count * row)
+    .sum
+    .toString
+
+def part2(input: String): String =
+  val lines = input.split('\n')
+  val border = lines.head.map(_ => '#').mkString + "##"
+  val grid = lines
+    .map(l => s"#$l#")
+    .prepended(border)
+    .appended(border)
+    .map(_.to(mutable.ArraySeq))
+
+  val coords =
+    for
+      y <- grid.indices
+      x <- grid.head.indices
+    yield (x, y)
+
+  enum Directions(
+      val coordinates: Seq[(Int, Int)],
+      val rangeToEdge: (Int, Int) => Seq[(Int, Int)]
+  ):
+    case North
+        extends Directions(
+          coords,
+          (x, y) => (y - 1 to (0, -1)).map((x, _))
+        )
+    case West
+        extends Directions(
+          coords.sortBy(_._1),
+          (x, y) => (x - 1 to (0, -1)).map((_, y))
+        )
+    case South
+        extends Directions(
+          coords.reverse,
+          (x, y) => (y + 1 until grid.length).map((x, _))
+        )
+    case East
+        extends Directions(
+          coords.sortBy(_._1).reverse,
+          (x, y) => (x + 1 until grid.length).map((_, y))
+        )
+
+  def cycle =
+    for d <- Directions.values do
+      for (x, y) <- d.coordinates do
+        if grid(y)(x) != 'O' then ()
+        else
+          d.rangeToEdge(x, y)
+            .takeWhile((xR, yR) => grid(yR)(xR) == '.')
+            .lastOption
+            .foreach((xR, yR) =>
+              grid(y)(x) = '.'
+              grid(yR)(xR) = 'O'
+            )
+
+  def cycleUntilRepeat: (Int, Int) =
+    val seen = mutable.Map.empty[String, Int]
+
+    @tailrec def aux(iter: Int): (Int, Int) =
+      cycle
+      val gridString = grid.map(_.mkString).mkString("\n")
+      seen.get(gridString) match
+        case Some(prevIterations) => (iter, iter - prevIterations)
+        case None =>
+          seen.put(gridString, iter)
+          aux(iter + 1)
+
+    aux(1)
+
+  val (repeatedIndex, repeatedLength) = cycleUntilRepeat
+  val cyclesLeft = (1_000_000_000 - repeatedIndex) % repeatedLength
+
+  for _ <- (0 until cyclesLeft) do cycle
+
+  grid
+    .map(_.count(_ == 'O'))
+    .reverse
+    .zipWithIndex
+    .map((count, row) => count * (row))
+    .sum
+    .toString