From ac5472acce4e5a134558d17025228a573f48cb00 Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Mon, 8 Dec 2025 12:02:51 +0100
Subject: [PATCH 1/2] Add code for day 8

---
 2025/src/day08.scala | 83 ++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 83 insertions(+)
 create mode 100644 2025/src/day08.scala

diff --git a/2025/src/day08.scala b/2025/src/day08.scala
new file mode 100644
index 0000000000..2c33294c9c
--- /dev/null
+++ b/2025/src/day08.scala
@@ -0,0 +1,83 @@
+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")
+
+
+/**************/
+/* Data Model */
+/**************/
+
+/** A junction box in 3D space with an associated circuit ID. */
+class Box(val x: Long, val y: Long, val z: Long, var circuit: Int):
+  def distanceSquare(other: Box): Long =
+    (x - other.x) * (x - other.x) + (y - other.y) * (y - other.y) + (z - other.z) * (z - other.z)
+
+
+/****************/
+/* Data Loading */
+/****************/
+
+/** Parses comma-separated coordinates from the given `line` into a `Box` with
+  * the given `circuit` ID.
+  */
+def parseBox(line: String, circuit: Int): Box =
+  val parts = line.split(",")
+  Box(parts(0).toLong, parts(1).toLong, parts(2).toLong, circuit)
+
+/** Parses the input, returning a sequence of `Box`es and all unique pairs
+  * of boxes sorted by distance.
+  */
+def load(input: String): (Seq[Box], Seq[(Box, Box)]) =
+  val lines = input.linesIterator.filter(_.nonEmpty)
+  val boxes = lines.zipWithIndex.map(parseBox).toSeq
+  val pairsByDistance = boxes.pairs.toSeq.sortBy((b1, b2) => b1.distanceSquare(b2))
+  (boxes, pairsByDistance)
+
+extension [T](self: Seq[T])
+  /** Generates all unique pairs (combinations of 2) from the sequence. */
+  def pairs: Iterator[(T, T)] =
+    self.combinations(2).map(pair => (pair(0), pair(1)))
+
+
+/**********/
+/* Part 1 */
+/**********/
+
+@main def part1: Unit =
+  println(s"The solution is ${part1(loadInput())}")
+
+def part1(input: String): Int =
+  val (boxes, pairsByDistance) = load(input)
+  for (b1, b2) <- pairsByDistance.take(1000) if b1.circuit != b2.circuit do
+    merge(b1.circuit, b2.circuit, boxes)
+  val sizes = boxes.groupBy(_.circuit).values.map(_.size).toSeq.sortBy(-_)
+  sizes.take(3).product
+
+/** Sets all boxes with circuit `c2` to circuit `c1`. */
+def merge(c1: Int, c2: Int, boxes: Seq[Box]): Unit =
+  for b <- boxes if b.circuit == c2 do b.circuit = c1
+
+
+/**********/
+/* Part 2 */
+/**********/
+
+@main def part2: Unit =
+  println(s"The solution is ${part2(loadInput())}")
+
+def part2(input: String): Long =
+  val (boxes, pairsByDistance) = load(input)
+  var n = boxes.length
+  boundary:
+    for (b1, b2) <- pairsByDistance if b1.circuit != b2.circuit do
+      merge(b1.circuit, b2.circuit, boxes)
+      n -= 1
+      if n <= 1 then
+        break(b1.x * b2.x)
+    throw Exception("Should not reach here")

From 05b9e2676d9e399184dddb6745d7a476da2390ad Mon Sep 17 00:00:00 2001
From: Matt Bovel <matthieu@bovel.net>
Date: Wed, 10 Dec 2025 10:09:26 +0100
Subject: [PATCH 2/2] Make `Box` a case class

---
 2025/src/day08.scala | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/2025/src/day08.scala b/2025/src/day08.scala
index 2c33294c9c..5d760a687a 100644
--- a/2025/src/day08.scala
+++ b/2025/src/day08.scala
@@ -14,7 +14,7 @@ def loadInput(): String = loadFileSync(s"$currentDir/../input/day08")
 /**************/
 
 /** A junction box in 3D space with an associated circuit ID. */
-class Box(val x: Long, val y: Long, val z: Long, var circuit: Int):
+case class Box(val x: Long, val y: Long, val z: Long, var circuit: Int):
   def distanceSquare(other: Box): Long =
     (x - other.x) * (x - other.x) + (y - other.y) * (y - other.y) + (z - other.z) * (z - other.z)