D24

src/main/kotlin/cz/glubo/adventofcode/Main.kt

@@ -331,6 +331,8 @@ fun main(args: Array<String>) {
             "2025day8p2" to InputToLongCommand { y2025day8part2(it) },
             "2025day10p1" to InputToLongCommand { y2025day10part1(it) },
             "2025day10p2" to InputToLongCommand { y2025day10part2(it) },
+            "2024day25p1" to InputToLongCommand { y2024day25part1(it) },
+            "2024day25p2" to InputToLongCommand { y2024day25part2(it) },
         )
 
     val cmd = CommandLine(MyHelpCommand())

src/main/kotlin/cz/glubo/adventofcode/utils/Utils.kt

@@ -32,6 +32,53 @@ data class IVec2(
     infix fun tcDistance(other: IVec2) = abs(this.x - other.x) + abs(this.y - other.y)
 }
 
+data class IVec3(
+    val x: Int,
+    val y: Int,
+    val z: Int,
+) {
+    operator fun plus(other: IVec3) =
+        IVec3(
+            this.x + other.x,
+            this.y + other.y,
+            this.z + other.z,
+        )
+
+    operator fun minus(other: IVec3) =
+        IVec3(
+            this.x - other.x,
+            this.y - other.y,
+            this.z - other.z,
+        )
+
+    operator fun times(scale: Int) =
+        IVec3(
+            scale * this.x,
+            scale * this.y,
+            scale * this.z,
+        )
+
+    infix fun dot(other: IVec3) =
+        this.x.toLong() * other.x +
+            this.y.toLong() * other.y +
+            this.z.toLong() * other.z
+
+    /**
+     * Calculates the taxicab distance between this vector and the given vector.
+     *
+     * The taxicab distance is the sum of the absolute differences of the corresponding coordinates of the vectors.
+     *
+     * @param other The vector to calculate the taxicab distance to.
+     * @return The taxicab distance between this vector and the given vector.
+     */
+    infix fun tcDistance(other: IVec3) = abs(this.x - other.x) + abs(this.y - other.y) + abs(this.z - other.z)
+
+    infix fun squareDistance(other: IVec3): Long {
+        val diff = this - other
+        return diff dot diff
+    }
+}
+
 enum class FullDirection(
     val vector: IVec2,
     val char: Char,

src/main/kotlin/cz/glubo/adventofcode/y2025/day8/Day8.kt

@@ -1,16 +1,130 @@
 package cz.glubo.adventofcode.y2025.day8
 
+import cz.glubo.adventofcode.utils.IVec3
 import cz.glubo.adventofcode.utils.input.Input
 import io.klogging.noCoLogger
+import kotlin.math.roundToLong
+import kotlin.math.sqrt
 
 val logger = noCoLogger({}.javaClass.toString())
 
-suspend fun y2025day8part1(input: Input): Long {
+class UnionFind(
+    size: Int,
+) {
+    val parents = MutableList(size) { it }
+
+    fun findRoot(x: Int): Int {
+        val parent = parents[x]
+        return if (parents[parent] != parent) {
+            findRoot(parent).also { parents[x] = it }
+        } else {
+            parent
+        }
+    }
+
+    fun markUnion(
+        x: Int,
+        y: Int,
+    ) {
+        val rootX = findRoot(x)
+        val rootY = findRoot(y)
+        parents[rootX] = rootY
+    }
+
+    fun sizes(): List<Int> =
+        parents
+            .groupBy { findRoot(it) }
+            .map { (_, it) -> it.size }
+}
+
+suspend fun y2025day8part1(
+    input: Input,
+    num: Int = 1000,
+): Long {
     logger.info("year 2025 day 8 part 1")
-    return 0
+    val points = mutableListOf<IVec3>()
+    input.lineFlow().collect { line ->
+        val (x, y, z) =
+            line
+                .split(',')
+                .map { it.toInt() }
+        points.add(IVec3(x, y, z))
+    }
+
+    data class Connection(
+        val i: Int,
+        val j: Int,
+        val squareLength: Long,
+    ) {
+        fun length() = sqrt(squareLength.toDouble()).roundToLong()
+    }
+
+    val allConnections =
+        points.indices.flatMap { i ->
+            (i + 1..<points.size).map { j ->
+                Connection(
+                    i,
+                    j,
+                    points[i] squareDistance points[j],
+                )
+            }
+        }
+    val chosenConnections =
+        allConnections
+            .sortedBy { it.squareLength }
+            .take(num)
+    val union = UnionFind(points.size)
+    chosenConnections.forEach { conn ->
+        union.markUnion(conn.i, conn.j)
+    }
+
+    return union
+        .sizes()
+        .sortedByDescending { it }
+        .take(3)
+        .fold(1L) { acc, i -> acc * i }
 }
 
 suspend fun y2025day8part2(input: Input): Long {
     logger.info("year 2025 day 8 part 2")
-    return 0
+    val points = mutableListOf<IVec3>()
+    input.lineFlow().collect { line ->
+        val (x, y, z) =
+            line
+                .split(',')
+                .map { it.toInt() }
+        points.add(IVec3(x, y, z))
+    }
+
+    data class Connection(
+        val i: Int,
+        val j: Int,
+        val squareLength: Long,
+    ) {
+        fun length() = sqrt(squareLength.toDouble()).roundToLong()
+    }
+
+    val allConnections =
+        points.indices
+            .flatMap { i ->
+                (i + 1..<points.size).map { j ->
+                    Connection(
+                        i,
+                        j,
+                        points[i] squareDistance points[j],
+                    )
+                }
+            }.sortedBy { it.squareLength }
+    val union = UnionFind(points.size)
+
+    var lastConnection: Connection
+    var i = 0
+    do {
+        val conn = allConnections[i]
+        union.markUnion(conn.i, conn.j)
+        lastConnection = conn
+        i++
+    } while (union.sizes().size > 1 && allConnections.indices.contains((i)))
+
+    return points[lastConnection.i].x.toLong() * points[lastConnection.j].x.toLong()
 }

src/test/kotlin/cz/glubo/adventofcode/y2025/day8/Day8Test.kt

@@ -14,17 +14,58 @@ class Day8Test :
             y2025day8part1(
                 TestInput(
                     """
+                    162,817,812
+                    57,618,57
+                    906,360,560
+                    592,479,940
+                    352,342,300
+                    466,668,158
+                    542,29,236
+                    431,825,988
+                    739,650,466
+                    52,470,668
+                    216,146,977
+                    819,987,18
+                    117,168,530
+                    805,96,715
+                    346,949,466
+                    970,615,88
+                    941,993,340
+                    862,61,35
+                    984,92,344
+                    425,690,689
                     """.trimIndent(),
                 ),
-            ) shouldBe 0
+                10,
+            ) shouldBe 40
         }
 
         "day8 example part 2 matches" {
             y2025day8part2(
                 TestInput(
                     """
+                    162,817,812
+                    57,618,57
+                    906,360,560
+                    592,479,940
+                    352,342,300
+                    466,668,158
+                    542,29,236
+                    431,825,988
+                    739,650,466
+                    52,470,668
+                    216,146,977
+                    819,987,18
+                    117,168,530
+                    805,96,715
+                    346,949,466
+                    970,615,88
+                    941,993,340
+                    862,61,35
+                    984,92,344
+                    425,690,689
                     """.trimIndent(),
                 ),
-            ) shouldBe 0
+            ) shouldBe 25272
         }
     })