Day 8

src/day08.scala

@@ -0,0 +1,59 @@
+package aoc
+package day08
+
+import scala.math.pow
+
+val dayNumber = "08"
+
+@main def part1: Unit =
+  println(part1(loadInput(dayNumber)))
+
+@main def part2: Unit =
+  println(part2(loadInput(dayNumber)))
+
+case class Box(x: Long, y: Long, z: Long):
+  def distanceSquared(other: Box): Double =
+    pow(x - other.x, 2) + pow(y - other.y, 2) + pow(z - other.z, 2)
+
+type Circuit = Set[Box]
+extension (circuit: Circuit)
+  def distances = circuit.toList
+    .combinations(2)
+    .collect {
+      case List(b1, b2) if b1 != b2 =>
+        (b1, b2, b1.distanceSquared(b2))
+    }.toList.sortBy(_._3)
+
+extension (circuits: Vector[Circuit])
+  def connect(b1: Box, b2: Box) =
+    val idx1 = circuits.indexWhere(_.contains(b1))
+    val idx2 = circuits.indexWhere(_.contains(b2))
+    val c1   = circuits(idx1)
+    val c2   = circuits(idx2)
+    circuits.updated(idx2, Set.empty).updated(idx1, c1 ++ c2).filter(_.nonEmpty)
+
+def part1(input: String): Long =
+  val boxes = input.split('\n').map { case s"$x,$y,$z" => Box(x.toInt, y.toInt, z.toInt) }.toSet
+
+  val circuits =
+    boxes.distances.take(1000).foldLeft(boxes.toVector.map(Set(_))) {
+      case (circuits, (b1, b2, _)) =>
+        circuits.connect(b1, b2)
+    }
+
+  circuits.toList.map(_.size).sorted.takeRight(3).reduce(_ * _)
+
+def part2(input: String): Long =
+  val boxes = input.split('\n').map { case s"$x,$y,$z" => Box(x.toInt, y.toInt, z.toInt) }.toSet
+
+  var lastDistance = Option.empty[(Box, Box)]
+
+  boxes.distances
+    .to(LazyList)
+    .scanLeft(boxes.toVector.map(Set(_))) { case (circuits, (b1, b2, _)) =>
+      lastDistance = Some(b1, b2)
+      circuits.connect(b1, b2)
+    }
+    .dropWhile(_.size > 1).head
+
+  lastDistance.map((b1, b2) => b1.x * b2.x).get