Year 2022 Day 23

Author: maneatingape

README.md

@@ -53,6 +53,7 @@ The minimal SBT project provides:
 | 20 | [Grove Positioning System](https://adventofcode.com/2022/day/20) | [Source](src/main/scala/AdventOfCode2022/Day20.scala) |
 | 21 | [Monkey Math](https://adventofcode.com/2022/day/21) | [Source](src/main/scala/AdventOfCode2022/Day21.scala) |
 | 22 | [Monkey Map](https://adventofcode.com/2022/day/22) | [Source](src/main/scala/AdventOfCode2022/Day22.scala) |
+| 23 | [Unstable Diffusion](https://adventofcode.com/2022/day/23) | [Source](src/main/scala/AdventOfCode2022/Day23.scala) |
 
 ## 2021
 

src/main/resources/AdventOfCode2022/Day23.txt

@@ -0,0 +1,71 @@
+...###.....#.#....##....#..###.....#.##.#..####..#.##.....##..#####..##
+#..##....#####...#.#.#############...#.######.#.##.##...####.#.#.#.#.##
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src/main/scala/AdventOfCode2022/Day23.scala

@@ -0,0 +1,65 @@
+package AdventOfCode2022
+
+object Day23:
+  val adjacent = Seq(Point(-1, -1), Point(0, -1), Point(1, -1), Point(-1, 0), Point(1, 0), Point(-1, 1), Point(0, 1), Point(1, 1))
+  val (north, south, west, east) = (Point(0, -1), Point(0, 1), Point(-1, 0), Point(1, 0))
+  val order = Seq(north, south, west, east)
+
+  case class Point(x: Int, y: Int):
+    def +(other: Point): Point = Point(x + other.x, y + other.y)
+
+  case class State(elves: Set[Point], moves: Seq[Point], stuck: Boolean)
+
+  def parse(input: Seq[String]): Set[Point] =
+    val points = for y <- input.indices; x <- input.head.indices if input(y)(x) != '.' yield Point(x, y)
+    points.toSet
+
+  def step(state: State): State =
+    val State(elves, moves, _) = state
+
+    val proposals = elves.map(elf => elf -> propose(elves, moves, elf))
+    val occurrences = proposals.toSeq.flatMap(_._2).groupMapReduce(identity)(_ => 1)(_ + _)
+    val valid = occurrences.filter((_, total) => total == 1).keySet
+    val next = proposals.map { (elf, proposal) =>
+      proposal.map(move => if valid.contains(move) then move else elf).getOrElse(elf)
+    }
+
+    State(next, moves.tail :+ moves.head, elves == next)
+  end step
+
+  def propose(elves: Set[Point], order: Seq[Point], elf: Point): Option[Point] =
+    val checks = adjacent.map(_ + elf).map(elves.contains)
+    val Seq(nw, n, ne, w, e, sw, s, se) = checks
+
+    if checks.exists(identity) then
+      order.find {
+        case `north` => !(nw || n || ne)
+        case `south` => !(sw || s || se)
+        case `west` => !(nw || w || sw)
+        case `east` => !(ne || e || se)
+      }
+      .map(_ + elf)
+    else None
+  end propose
+
+  def part1(input: Seq[String]): Int =
+    val start = State(parse(input), order, false)
+    val elves = Iterator.iterate(start)(step).drop(10).next.elves
+
+    val minX = elves.map(_.x).min
+    val maxX = elves.map(_.x).max
+    val minY = elves.map(_.y).min
+    val maxY = elves.map(_.y).max
+
+    val points = for x <- minX to maxX; y <- minY to maxY yield Point(x, y)
+    points.filterNot(elves.contains).size
+  end part1
+
+  def part2(input: Seq[String]): Int =
+    val start = State(parse(input), order, false)
+    Iterator.iterate(start)(step).indexWhere(_.stuck == true)
+
+  def main(args: Array[String]): Unit =
+    val data = io.Source.fromResource("AdventOfCode2022/Day23.txt").getLines().toSeq
+    println(part1(data))
+    println(part2(data))

src/test/scala/AdventOfCode2022/Day23Suite.scala

@@ -0,0 +1,21 @@
+package AdventOfCode2022
+
+import org.scalatest.funsuite.AnyFunSuite
+
+class Day23Suite extends AnyFunSuite:
+  val sample = Seq(
+    "....#..",
+    "..###.#",
+    "#...#.#",
+    ".#...##",
+    "#.###..",
+    "##.#.##",
+    ".#..#..")
+
+  test("Part 1 should handle sample input correctly") {
+    assert(Day23.part1(sample) == 110)
+  }
+
+  test("Part 2 should handle sample input correctly") {
+    assert(Day23.part2(sample) == 20)
+  }