Solution Day 25, part one (Code Chronicle)

Author: rhaendel

src/main/kotlin/de/ronny_h/aoc/year24/day25/CodeChronicle.kt

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+package de.ronny_h.aoc.year24.day25
+
+import de.ronny_h.aoc.AdventOfCode
+import de.ronny_h.aoc.extensions.combinationsOf
+import de.ronny_h.aoc.extensions.split
+
+fun main() = CodeChronicle().run(2993, 0)
+
+class CodeChronicle : AdventOfCode<Int>(2024, 25) {
+    companion object {
+        private val filled = '#'
+        private val empty = '.'
+
+        fun List<String>.convertToLocksAndKeys() = split()
+            .map { block ->
+                if (block.first().all { it == filled } && block.last().all { it == empty }) {
+                    Lock(block.countHeights())
+                } else if (block.first().all { it == empty } && block.last().all { it == filled }) {
+                    Key(block.countHeights())
+                } else {
+                    error("The current block is neither a lock nor a key: '$block'")
+                }
+            }
+
+        fun Key.fitsIntoLockWithoutOverlapping(lock: Lock) = (0..4).all { column ->
+            this.heights[column] + lock.pins[column] <= 5
+        }
+
+        private fun List<String>.countHeights(): List<Int> = (0..4).map { column ->
+            count { it[column] == filled } - 1
+        }
+    }
+
+    @Suppress("UNCHECKED_CAST")
+    override fun part1(input: List<String>): Int {
+        val (keys, locks) = input
+            .convertToLocksAndKeys()
+            .partition { it is Key } as Pair<List<Key>, List<Lock>>
+        return combinationsOf(keys, locks).count { (key, lock) ->
+            key.fitsIntoLockWithoutOverlapping(lock)
+        }
+    }
+
+    override fun part2(input: List<String>): Int {
+        TODO("Not yet implemented")
+    }
+}
+
+sealed interface VirtualFivePinTumbler
+
+data class Lock(val pins: List<Int>) : VirtualFivePinTumbler {
+    init {
+        require(pins.size == 5) { "Number of pins is not 5: $pins" }
+    }
+}
+
+data class Key(val heights: List<Int>) : VirtualFivePinTumbler {
+    init {
+        require(heights.size == 5) { "Number of heights is not 5: $heights" }
+    }
+}

src/test/kotlin/de/ronny_h/aoc/year24/day25/CodeChronicleTest.kt

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+package de.ronny_h.aoc.year24.day25
+
+import de.ronny_h.aoc.extensions.asList
+import de.ronny_h.aoc.year24.day25.CodeChronicle.Companion.convertToLocksAndKeys
+import de.ronny_h.aoc.year24.day25.CodeChronicle.Companion.fitsIntoLockWithoutOverlapping
+import io.kotest.core.spec.style.StringSpec
+import io.kotest.matchers.shouldBe
+
+class CodeChronicleTest : StringSpec({
+
+    val smallInput = """
+        #####
+        .####
+        .####
+        .####
+        .#.#.
+        .#...
+        .....
+        
+        .....
+        #....
+        #....
+        #...#
+        #.#.#
+        #.###
+        #####
+    """.asList()
+
+    val input = """
+        #####
+        .####
+        .####
+        .####
+        .#.#.
+        .#...
+        .....
+        
+        #####
+        ##.##
+        .#.##
+        ...##
+        ...#.
+        ...#.
+        .....
+        
+        .....
+        #....
+        #....
+        #...#
+        #.#.#
+        #.###
+        #####
+        
+        .....
+        .....
+        #.#..
+        ###..
+        ###.#
+        ###.#
+        #####
+        
+        .....
+        .....
+        .....
+        #....
+        #.#..
+        #.#.#
+        #####
+    """.asList()
+
+    "convert smallInput to locks and keys" {
+        smallInput.convertToLocksAndKeys() shouldBe listOf(Lock(listOf(0,5,3,4,3)), Key(listOf(5,0,2,1,3)))
+    }
+
+    "a key fits into a lock without overlapping" {
+        Key(listOf(3,3,3,3,3)).fitsIntoLockWithoutOverlapping(Lock(listOf(2,2,2,2,2))) shouldBe true
+    }
+
+    "a key with a too high height does not fit into a lock without overlapping" {
+        Key(listOf(3,3,4,3,3)).fitsIntoLockWithoutOverlapping(Lock(listOf(2,2,2,2,2))) shouldBe false
+    }
+
+    "part1: In the input should be 3 unique lock/key pairs that fit together without overlapping in any column" {
+        CodeChronicle().part1(input) shouldBe 3
+    }
+})