Day 08 2024 (#267)

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2024/calendar/day08/Day08.kt

@@ -0,0 +1,91 @@
+package me.peckb.aoc._2024.calendar.day08
+
+import me.peckb.aoc.generators.CombinationsGenerator
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+
+class Day08 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).read { lines ->
+    val (maxY, maxX, antenna) = findAntenna(lines)
+    val antinodes = findAntinodes(maxY, maxX, antenna, false)
+
+    antinodes.size
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).read { lines ->
+    val (maxY, maxX, antenna) = findAntenna(lines)
+    val antinodes = findAntinodes(maxY, maxX, antenna, true)
+
+    antinodes.plus(
+      antenna.values.flatMap { it.toList() }
+    ).size
+  }
+
+  private fun findAntenna(input: Sequence<String>): AntennaData {
+    val antenna = mutableMapOf<Char, Array<Location>>()
+
+    var maxY = 0
+    var maxX = 0
+
+    input.forEachIndexed { yIndex, line ->
+      maxY = maxOf(maxY, yIndex)
+      line.forEachIndexed { xIndex, space ->
+        maxX = maxOf(maxX, xIndex)
+        when (space) {
+          '.' -> { /* skip */ }
+          else -> antenna.merge(space, arrayOf(Location(yIndex, xIndex))) { a, b -> a + b }
+        }
+      }
+    }
+
+    return AntennaData(maxY, maxX, antenna)
+  }
+
+  private fun findAntinodes(
+    maxY: Int,
+    maxX: Int,
+    antenna: Map<Char, Array<Location>>,
+    forever: Boolean
+  ): Set<Location> {
+    val antinodes = mutableSetOf<Location>()
+
+    fun find(antenna: Location, xDelta: Int, yDelta: Int, mover: (Int, Int) -> Int) {
+      var inbounds = forever
+      var frequency = 1
+
+      val (y, x) = antenna
+
+      do {
+        val possibleY = mover(y, (yDelta * frequency))
+        val possibleX = mover(x, (xDelta * frequency))
+
+        if (possibleX in 0..maxX && possibleY in 0..maxY) {
+          antinodes.add(Location(possibleY, possibleX))
+          frequency++
+        } else {
+          inbounds = false
+        }
+      } while (inbounds)
+    }
+
+    antenna.forEach { (_, locations) ->
+      val combinations = CombinationsGenerator.findCombinations(locations, 2)
+
+      combinations.forEach { (a, b) ->
+        val xDelta = a.x - b.x
+        val yDelta = a.y - b.y
+
+        find(a, xDelta, yDelta, Int::plus)
+        find(b, xDelta, yDelta, Int::minus)
+      }
+    }
+
+    return antinodes
+  }
+}
+
+data class AntennaData(val maxY: Int, val maxX: Int, val locations: Map<Char, Array<Location>>)
+
+data class Location(val y: Int, val x: Int)

src/main/kotlin/me/peckb/aoc/_2024/calendar/day08/README.md

@@ -0,0 +1 @@
+## [Day 8: Resonant Collinearity](https://adventofcode.com/2024/day/8)

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

@@ -7,6 +7,7 @@ import me.peckb.aoc._2024.calendar.day04.Day04Test
 import me.peckb.aoc._2024.calendar.day05.Day05Test
 import me.peckb.aoc._2024.calendar.day06.Day06Test
 import me.peckb.aoc._2024.calendar.day07.Day07Test
+import me.peckb.aoc._2024.calendar.day08.Day08Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -22,4 +23,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day05Test: Day05Test)
   fun inject(day06Test: Day06Test)
   fun inject(day07Test: Day07Test)
+  fun inject(day08Test: Day08Test)
 }

src/test/kotlin/me/peckb/aoc/_2024/calendar/day08/Day08Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2024.calendar.day08
+
+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 Day08Test {
+  @Inject
+  lateinit var day08: Day08
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay08PartOne() {
+    assertEquals(369, day08.partOne(DAY_08))
+  }
+
+  @Test
+  fun testDay08PartTwo() {
+    assertEquals(1169, day08.partTwo(DAY_08))
+  }
+
+  companion object {
+    private const val DAY_08: String = "advent-of-code-input/2024/day08.input"
+  }
+}