Day 18 2024 (#281)

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2024/calendar/day18/Day18.kt

@@ -0,0 +1,91 @@
+package me.peckb.aoc._2024.calendar.day18
+
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+import me.peckb.aoc.pathing.GenericIntDijkstra
+
+class Day18 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).readAs(::location) { locations ->
+    val area = Array(HEIGHT) { Array(WIDTH) { Memory.EMPTY } }
+
+    locations.take(1024).forEach { (y, x) ->
+      area[y][x] = Memory.CORRUPTED
+    }
+
+    val solver = object : GenericIntDijkstra<Location>() { }
+
+    val solutions = solver.solve(
+      Location(0, 0).withArea(area).withPreviousPath(emptyList()),
+      Location(HEIGHT - 1, WIDTH- 1)
+    )
+
+    solutions[Location(HEIGHT - 1, WIDTH- 1)]
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).readAs(::location) { locations ->
+    val area = Array(HEIGHT) { Array(WIDTH) { Memory.EMPTY } }
+    val start = Location(0, 0).withArea(area).withPreviousPath(emptyList())
+    val end = Location(HEIGHT - 1, WIDTH - 1)
+
+    val locationList = locations.toList()
+
+    var counter = 1024
+    locationList.take(1024).forEach { (y, x) -> area[y][x] = Memory.CORRUPTED }
+
+    var solutions: Map<Location, Int> = emptyMap()
+    val solver = object : GenericIntDijkstra<Location>() {}
+    search@ do {
+      val next = locationList[counter++]
+      area[next.y][next.x] = Memory.CORRUPTED
+
+      if (solutions.entries.firstOrNull { it.key == end }?.key?.path?.contains(next) == false) {
+        continue@search
+      }
+
+      solutions = solver.solve(start, end)
+    } while(solutions[end] != null)
+
+    locationList[counter - 1].let { "${it.x},${it.y}" }
+  }
+
+  private fun location(line: String) = line.split(",")
+    .map { it.toInt() }
+    .let { (x, y) -> Location(y, x) }
+
+  companion object {
+    const val WIDTH  = 71
+    const val HEIGHT = 71
+  }
+}
+
+data class Location(val y: Int, val x: Int) : GenericIntDijkstra.DijkstraNode<Location> {
+  lateinit var path: List<Location>
+  lateinit var area: Array<Array<Memory>>
+
+  fun withArea(area: Array<Array<Memory>>)   = apply { this.area = area }
+  fun withPreviousPath(path: List<Location>) = apply { this.path = path.plus(this) }
+
+  override fun neighbors(): Map<Location, Int> {
+    return Direction.entries.mapNotNull { d ->
+      val (newY, newX) = d.yDelta + y to d.xDelta + x
+      if (newY in area.indices && newX in area[newY].indices && area[newY][newX] == Memory.EMPTY) {
+        Location(newY, newX).withArea(area).withPreviousPath(path)
+      } else { null }
+    }.associateWith { 1 }
+  }
+}
+
+enum class Direction(val yDelta: Int, val xDelta: Int) {
+  N(-1, 0),
+  E(0, 1),
+  S(1, 0),
+  W(0, -1);
+}
+
+enum class Memory(val s: String) {
+  EMPTY("."), CORRUPTED("#");
+
+  override fun toString(): String = s
+}

src/main/kotlin/me/peckb/aoc/_2024/calendar/day18/README.md

@@ -0,0 +1 @@
+## [Day 18: RAM Run](https://adventofcode.com/2024/day/18)

src/test/kotlin/me/peckb/aoc/_2024/TestDayComponent.kt

@@ -17,6 +17,7 @@ import me.peckb.aoc._2024.calendar.day14.Day14Test
 import me.peckb.aoc._2024.calendar.day15.Day15Test
 import me.peckb.aoc._2024.calendar.day16.Day16Test
 import me.peckb.aoc._2024.calendar.day17.Day17Test
+import me.peckb.aoc._2024.calendar.day18.Day18Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -42,4 +43,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day15Test: Day15Test)
   fun inject(day16Test: Day16Test)
   fun inject(day17Test: Day17Test)
+  fun inject(day18Test: Day18Test)
 }

src/test/kotlin/me/peckb/aoc/_2024/calendar/day18/Day18Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2024.calendar.day18
+
+import javax.inject.Inject
+
+import me.peckb.aoc._2024.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day18Test {
+  @Inject
+  lateinit var day18: Day18
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay18PartOne() {
+    assertEquals(416, day18.partOne(DAY_18))
+  }
+
+  @Test
+  fun testDay18PartTwo() {
+    assertEquals("50,23", day18.partTwo(DAY_18))
+  }
+
+  companion object {
+    private const val DAY_18: String = "advent-of-code-input/2024/day18.input"
+  }
+}