Day 18

aoc/src/dev/ctsk/aoc/DisjointSets.scala

@@ -0,0 +1,27 @@
+package dev.ctsk.aoc
+
+import scala.collection.mutable
+
+case class DisjointSets[A](members: Seq[A]):
+  private val parent = mutable.Map.from(members.zip(members))
+  private val rank = mutable.Map.from(members.map(_ -> 1))
+
+  def joint(m1: A, m2: A): Boolean = find(m1) == find(m2)
+
+  def find(member: A): A =
+    val up = parent(member)
+    if up == member then up
+    else {
+      val root = find(up); parent(member) = root; root
+    }
+
+  def union(m1: A, m2: A): Unit =
+    val p1 = find(m1);
+    val p2 = find(m2)
+    if p1 == p2 then return
+    val r1 = rank(p1);
+    val r2 = rank(p2)
+    r1.compare(r2) match
+      case k if k < 0 => parent(p1) = p2
+      case 0          => parent(p1) = p2; rank(p2) += 1
+      case k if k > 0 => parent(p2) = p1

aoc/src/dev/ctsk/aoc/Grid.scala

@@ -11,8 +11,7 @@ case class Point(x: Int, y: Int):
   def *(n: Int): Point = Point(n * x, n * y)
   def reduce: Point = { val g = gcd(x.abs, y.abs); Point(x / g, y / g) }
 
-val directions =
-  Seq(Direction.Up, Direction.Right, Direction.Down, Direction.Left)
+val DIRS = Seq(Direction.Up, Direction.Right, Direction.Down, Direction.Left)
 
 object Direction:
   def from(c: Char): Direction =

aoc/src/dev/ctsk/aoc/Main.scala

@@ -19,7 +19,8 @@ val solvers = Map[Int, Solver](
   14 -> Day14,
   15 -> Day15,
   16 -> Day16,
-  17 -> Day17
+  17 -> Day17,
+  18 -> Day18
 )
 
 def runSolver(solver: Solver, input: os.Path): Unit =

aoc/src/dev/ctsk/aoc/days/Day16.scala

@@ -43,7 +43,7 @@ object Day16 extends Solver(16):
       search(Pose(start, Direction.Right))
     }
 
-    val endPose = directions.map(Pose(end, _)).minBy(distance(_))
+    val endPose = DIRS.map(Pose(end, _)).minBy(distance(_))
 
     val p1 = distance(endPose)
 

aoc/src/dev/ctsk/aoc/days/Day17.scala

@@ -45,10 +45,10 @@ object Day17 extends Solver(17):
 
     def rec(pos: Int = 0, acc: Long = 0): Option[Long] =
       if pos >= target.length then return Some(acc)
+
       def check(aVal: Long): Boolean =
-        machine.execute(initialRegs.updated('A', aVal), Some(1)).head == target(
-          pos
-        )
+        machine.execute(initialRegs.updated('A', aVal), Some(1)).head
+          == target(pos)
 
       (0 until 8)
         .map((acc << 3) + _)
@@ -61,13 +61,10 @@ object Day17 extends Solver(17):
   override def run(input: os.ReadablePath): (Timings, Solution) =
     val Array(initial_, code_) = os.read(input).split("\n\n")
     val initialRegs = initial_.linesIterator
-      .map(line => {
-        val spl = line.split(" ");
-        (spl(1)(0) -> spl(2).toLong)
-      })
+      .map(_.split(" "))
+      .map(a => a(1)(0) -> a(2).toLong)
       .toMap
-    val code = longs(code_)
-    val machine = Machine(code)
+    val machine = Machine(longs(code_).toArray)
 
     val (p1_time, p1_solution) = timed { part1(machine, initialRegs) }
     val (p2_time, p2_solution) = timed { part2(machine, initialRegs) }

aoc/src/dev/ctsk/aoc/days/Day18.scala

@@ -0,0 +1,60 @@
+package dev.ctsk.aoc.days
+
+import dev.ctsk.aoc.*
+
+import scala.collection.mutable
+import scala.util.boundary
+import scala.util.boundary.break
+
+object Day18 extends Solver(18):
+  val SIZE = 70; val P1_COUNT = 1024
+
+  def part1(grid: Grid[Char], coords: Seq[Point]): Int =
+    for coord <- coords.take(P1_COUNT) do grid(coord) = '#'
+    val dist = Grid(Array.fill(SIZE + 1, SIZE + 1)(-1))
+    val dq = mutable.ArrayDeque((0, Point(0, 0)))
+
+    while dq.nonEmpty do
+      val (distance, pt) = dq.removeHead()
+      for
+        adj <- DIRS.map(_(pt))
+        if grid(adj).contains('.')
+        if dist(adj).contains(-1)
+      do
+        dist(adj) = (distance + 1)
+        dq += ((distance + 1, adj))
+
+    dist(Point(SIZE, SIZE)).get
+
+  def part2(grid: Grid[Char], coords: Seq[Point]): Point =
+    for coord <- coords do grid(coord) = '#'
+
+    val sets = DisjointSets(grid.points)
+    for
+      point <- grid.points
+      adj <- DIRS.map(_(point))
+      if grid(point).contains('.')
+      if grid(adj).contains('.')
+    do sets.union(point, adj)
+
+    boundary:
+      for coord <- coords.reverse do
+        grid(coord) = '.'
+        for pt <- DIRS.map(_(coord)) if grid(pt).contains('.') do
+          sets.union(coord, pt)
+        if sets.joint(Point(0, 0), Point(SIZE, SIZE)) then break(coord)
+
+      coords.head
+
+  override def run(input: os.ReadablePath): (Timings, Solution) =
+    val grid = Grid(Array.fill(SIZE + 1, SIZE + 1)('.'))
+    val (pre_time, coords) = timed {
+      os.read.lines(input).map(longs).map(v => Point.of(v(0), v(1)))
+    }
+    val (p1_time, p1) = timed { part1(grid, coords) }
+    val (p2_time, p2) = timed { part2(grid, coords) }
+
+    (
+      Timings(pre_time, p1_time, p2_time),
+      Solution(Int.box(p1), f"${p2.x},${p2.y}")
+    )

data/18.ans

@@ -0,0 +1,2 @@
+262
+22,20