Merge pull request #120 from ephemient/kt/day18

Day 18: RAM Run

README.md

@@ -22,4 +22,4 @@ Development occurs in language-specific directories:
 |[Day15.hs](hs/src/Day15.hs)|[Day15.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day15.kt)|[day15.py](py/aoc2024/day15.py)|[day15.rs](rs/src/day15.rs)|
 |[Day16.hs](hs/src/Day16.hs)|[Day16.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day16.kt)|[day16.py](py/aoc2024/day16.py)|[day16.rs](rs/src/day16.rs)|
 |[Day17.hs](hs/src/Day17.hs)|[Day17.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day17.kt)|[day17.py](py/aoc2024/day17.py)|[day17.rs](rs/src/day17.rs)|
-|[Day18.hs](hs/src/Day18.hs)||||
+|[Day18.hs](hs/src/Day18.hs)|[Day18.kt](kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day18.kt)|||

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day11Bench.kt

@@ -28,4 +28,4 @@ class Day11Bench {
         bh.consume(day11.part1())
         bh.consume(day11.part2())
     }
-}
+}

kt/aoc2024-exe/src/commonBench/kotlin/com/github/ephemient/aoc2024/exe/Day18Bench.kt

@@ -0,0 +1,31 @@
+package com.github.ephemient.aoc2024.exe
+
+import com.github.ephemient.aoc2024.Day18
+import kotlinx.benchmark.Benchmark
+import kotlinx.benchmark.Blackhole
+import kotlinx.benchmark.Scope
+import kotlinx.benchmark.Setup
+import kotlinx.benchmark.State
+
+@State(Scope.Benchmark)
+class Day18Bench {
+    private lateinit var input: String
+
+    @Setup
+    fun setup() {
+        input = getDayInput(18)
+    }
+
+    @Benchmark
+    fun part1() = Day18(input).part1()
+
+    @Benchmark
+    fun part2() = Day18(input).part2()
+
+    @Benchmark
+    fun solve(bh: Blackhole) {
+        val day18 = Day18(input)
+        bh.consume(day18.part1())
+        bh.consume(day18.part2())
+    }
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Day18.kt

@@ -0,0 +1,39 @@
+package com.github.ephemient.aoc2024
+
+class Day18(input: String, private val size: Int = 70) {
+    private val coords = input.lineSequence().mapNotNull { line ->
+        val x = line.substringBefore(',').toIntOrNull() ?: return@mapNotNull null
+        val y = line.substringAfter(',').toIntOrNull() ?: return@mapNotNull null
+        x to y
+    }.toList()
+
+    private fun findPath(obstacles: Iterable<IntPair>): Set<IntPair>? {
+        val visited = obstacles.toMutableSet()
+        val queue = ArrayDeque<Node>()
+        queue.add(Node(0, 0))
+        while (queue.isNotEmpty()) {
+            val node = queue.removeFirst()
+            val (x, y) = node
+            if (x == size && y == size) return generateSequence(node) { it.next }.map { it.x to it.y }.toSet()
+            if (!visited.add(x to y)) continue
+            if (x > 0) queue.addLast(Node(x - 1, y, node))
+            if (y > 0) queue.addLast(Node(x, y - 1, node))
+            if (y < size) queue.addLast(Node(x, y + 1, node))
+            if (x < size) queue.addLast(Node(x + 1, y, node))
+        }
+        return null
+    }
+
+    fun part1(limit: Int = 1024): Int? = findPath(coords.subList(0, limit))?.size?.minus(1)
+
+    fun part2(): String? {
+        var i = 0
+        while (i < coords.size) {
+            val path = findPath(coords.subList(0, i + 1)) ?: return coords[i].let { (x, y) -> "$x,$y" }
+            do i++ while (i < coords.size && coords[i] !in path)
+        }
+        return null
+    }
+
+    private data class Node(val x: Int, val y: Int, val next: Node? = null)
+}

kt/aoc2024-lib/src/commonMain/kotlin/com/github/ephemient/aoc2024/Days.kt

@@ -18,6 +18,7 @@ val days: List<Day> = listOf(
     Day(15, ::Day15, Day15::part1, Day15::part2),
     Day(16, ::Day16, Day16::part1, Day16::part2),
     Day(17, ::Day17, Day17::part1, Day17::part2),
+    Day(18, ::Day18, Day18::part1, Day18::part2),
 )
 
 data class Day(

kt/aoc2024-lib/src/commonTest/kotlin/com/github/ephemient/aoc2024/Day18Test.kt

@@ -0,0 +1,47 @@
+package com.github.ephemient.aoc2024
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day18Test {
+    @Test
+    fun part1() {
+        assertEquals(22, Day18(example, 6).part1(12))
+    }
+
+    @Test
+    fun part2() {
+        assertEquals("6,1", Day18(example, 6).part2())
+    }
+
+    companion object {
+        private val example =
+            """
+            |5,4
+            |4,2
+            |4,5
+            |3,0
+            |2,1
+            |6,3
+            |2,4
+            |1,5
+            |0,6
+            |3,3
+            |2,6
+            |5,1
+            |1,2
+            |5,5
+            |2,5
+            |6,5
+            |1,4
+            |0,4
+            |6,4
+            |1,1
+            |6,1
+            |1,0
+            |0,5
+            |1,6
+            |2,0
+            |""".trimMargin()
+    }
+}