Solution 2025-10 part 1

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year2025/day10/Day10.kt

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+package de.ronny_h.aoc.year2025.day10
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.memoize
+import de.ronny_h.aoc.year2025.day10.LightState.OFF
+import de.ronny_h.aoc.year2025.day10.LightState.ON
+
+fun main() = Day10().run(481, 0)
+
+class Day10 : AdventOfCode<Int>(2025, 10) {
+    override fun part1(input: List<String>): Int {
+        var i = 0
+        return input.parseMachineDescriptions().sumOf {
+            i++
+            val result = Machine(it).configureIndicatorLights()
+            println("machine $i: $result")
+            result
+        }
+    }
+
+    override fun part2(input: List<String>): Int {
+        return 0
+    }
+}
+
+// [.##.] (3) (1,3) (2) (2,3) (0,2) (0,1) {3,5,4,7}
+fun List<String>.parseMachineDescriptions(): List<MachineDescription> =
+    map { line ->
+        val indicatorLights = line.substringBefore("] (").drop(1)
+            .map { if (it == '#') ON else OFF }
+        val wiringSchematics = line.substringAfter("] ").substringBefore(" {")
+            .split(" ").map { it.drop(1).dropLast(1).split(",").map(String::toInt) }
+        val joltage = line.substringAfter(") {").dropLast(1).split(",").map(String::toInt)
+        MachineDescription(indicatorLights, wiringSchematics, joltage)
+    }
+
+
+data class MachineDescription(
+    val indicatorLights: List<LightState>,
+    val wiringSchematics: List<List<Int>>,
+    val joltage: List<Int>
+)
+
+enum class LightState {
+    OFF, ON;
+
+    fun toggle() = when (this) {
+        OFF -> ON
+        ON -> OFF
+    }
+}
+
+class Machine(private val description: MachineDescription, private val maxPressCount: Int = 7) {
+    private val indicatorLightsOff = List(description.indicatorLights.size) { OFF }
+    private val buttons = description.wiringSchematics
+
+    // determine the fewest total presses
+    fun configureIndicatorLights(): Int {
+        val target = description.indicatorLights
+
+        data class RecursiveState(val state: List<LightState>, val buttonsToPress: List<Int>, val pressCount: Int)
+
+        lateinit var pressButtons: (RecursiveState) -> Int
+        pressButtons = { s ->
+            if (s.pressCount == maxPressCount) {
+                maxPressCount
+            } else {
+                val newState = s.state.toMutableList()
+                s.buttonsToPress.forEach { newState[it] = newState[it].toggle() }
+                if (newState.contentEquals(target)) {
+                    s.pressCount
+                } else {
+                    buttons.minOf { pressButtons(RecursiveState(newState.toList(), it, s.pressCount + 1)) }
+                }
+            }
+        }
+
+        val pressButtonsMemoized = pressButtons.memoize()
+
+        return buttons.minOf { pressButtonsMemoized(RecursiveState(indicatorLightsOff, it, 1)) }
+    }
+}
+
+fun <T> MutableList<T>.contentEquals(other: List<T>): Boolean {
+    if (size != other.size) return false
+    forEachIndexed { i, element -> if (other[i] != element) return false }
+    return true
+}

src/test/kotlin/de/ronny_h/aoc/year2025/day10/Day10Test.kt

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+package de.ronny_h.aoc.year2025.day10
+
+import de.ronny_h.aoc.extensions.asList
+import de.ronny_h.aoc.year2025.day10.LightState.OFF
+import de.ronny_h.aoc.year2025.day10.LightState.ON
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class Day10Test : StringSpec({
+
+    val input = """
+        [.##.] (3) (1,3) (2) (2,3) (0,2) (0,1) {3,5,4,7}
+        [...#.] (0,2,3,4) (2,3) (0,4) (0,1,2) (1,2,3,4) {7,5,12,7,2}
+        [.###.#] (0,1,2,3,4) (0,3,4) (0,1,2,4,5) (1,2) {10,11,11,5,10,5}
+    """.asList()
+
+    "parse" {
+        """
+            [.##.] (3) (1,3) {3,5,4}
+            [.#] (0,2,3,4) {7,5}
+        """.asList().parseMachineDescriptions() shouldBe listOf(
+            MachineDescription(listOf(OFF, ON, ON, OFF), listOf(listOf(3), listOf(1, 3)), listOf(3, 5, 4)),
+            MachineDescription(listOf(OFF, ON), listOf(listOf(0, 2, 3, 4)), listOf(7, 5)),
+        )
+    }
+
+    "contentEquals" {
+        mutableListOf(1, 2).contentEquals(listOf(1, 2)) shouldBe true
+        mutableListOf(1, 2).contentEquals(listOf(1, 2, 3)) shouldBe false
+        mutableListOf(1, 2).contentEquals(listOf(1, 3)) shouldBe false
+    }
+
+    "configureIndicatorLights" {
+        val descriptions = input.parseMachineDescriptions()
+        Machine(descriptions[0], 5).configureIndicatorLights() shouldBe 2
+        Machine(descriptions[1], 5).configureIndicatorLights() shouldBe 3
+        Machine(descriptions[2], 5).configureIndicatorLights() shouldBe 2
+    }
+
+    "part 1" {
+        Day10().part1(input) shouldBe 7
+    }
+
+    "part 2" {
+        val input = listOf("")
+        Day10().part2(input) shouldBe 0
+    }
+})