Add code for day 8

Author: mbovel

2025/src/day08.scala

@@ -0,0 +1,62 @@
+package day08
+
+import scala.util.boundary
+import scala.util.boundary.break
+
+import locations.Directory.currentDir
+import inputs.Input.loadFileSync
+
+def loadInput(): String = loadFileSync(s"$currentDir/../input/day08")
+
+class Point(val x: Long, val y: Long, val z: Long, var circuit: Int):
+  def distance(p: Point): Long =
+    (x - p.x) * (x - p.x) + (y - p.y) * (y - p.y) + (z - p.z) * (z - p.z)
+
+/** Parses comma-separated coordinates from the given `line` into a `Point`
+  * with the given `circuit` ID.
+  */
+def point(line: String, circuit: Int): Point =
+  val parts = line.split(",")
+  Point(parts(0).toLong, parts(1).toLong, parts(2).toLong, circuit)
+
+/** Parses the input file at `path`, returning a sequence of `Point`s and all
+  * unique pairs of points sorted by distance.
+  */
+def load(input: String): (Seq[Point], Seq[(Point, Point)]) =
+  val lines = input.linesIterator.filter(_.nonEmpty)
+  val points = lines.zipWithIndex.map(point).toSeq
+  val pairsByDistance = points.pairs.toSeq.sortBy((p1, p2) => p1.distance(p2))
+  (points, pairsByDistance)
+
+/** Sets all points in `points` with circuit `c2` to circuit `c1`. */
+def merge(c1: Int, c2: Int, points: Seq[Point]): Unit =
+  for p <- points if p.circuit == c2 do p.circuit = c1
+
+extension [T](self: Seq[T])
+  /** Generates all unique pairs (combinations of 2) from given the sequence. */
+  def pairs: Iterator[(T, T)] =
+    self.combinations(2).map(pair => (pair(0), pair(1)))
+
+@main def part1: Unit =
+  println(s"The solution is ${part1(loadInput())}")
+
+def part1(input: String): Int =
+  val (points, pairsByDistance) = load(input)
+  for (p1, p2) <- pairsByDistance.take(1000) if p1.circuit != p2.circuit do
+    merge(p1.circuit, p2.circuit, points)
+  val sizes = points.groupBy(_.circuit).values.map(_.size).toSeq.sortBy(-_)
+  sizes.take(3).product
+
+@main def part2: Unit =
+  println(s"The solution is ${part2(loadInput())}")
+
+def part2(input: String): Long =
+  val (points, pairsByDistance) = load(input)
+  var n = points.length
+  boundary:
+    for (p1, p2) <- pairsByDistance if p1.circuit != p2.circuit do
+      merge(p1.circuit, p2.circuit, points)
+      n -= 1
+      if n <= 1 then
+        break(p1.x * p2.x)
+    throw Exception("Should not reach here")