Day 04 2024 (#262)

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2024/calendar/day04/Day04.kt

@@ -0,0 +1,63 @@
+package me.peckb.aoc._2024.calendar.day04
+
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+
+class Day04 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).read { lines ->
+    val (xLocations, area) = setup(lines, 'X')
+
+    xLocations.sumOf { (x, y) ->
+      val N  = area.findXMAS(y, -1, x,  0)
+      val NE = area.findXMAS(y, -1, x,  1)
+      val E  = area.findXMAS(y,  0, x,  1)
+      val SE = area.findXMAS(y,  1, x,  1)
+      val S  = area.findXMAS(y,  1, x,  0)
+      val SW = area.findXMAS(y,  1, x, -1)
+      val W  = area.findXMAS(y,  0, x, -1)
+      val NW = area.findXMAS(y, -1, x, -1)
+
+      listOf(N, NE, E, SE, S, SW, W, NW).count { it == "XMAS" }
+    }
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).read { lines ->
+    val (aLocations, area) = setup(lines, 'A')
+
+    aLocations.count { (x, y) ->
+      val NE = area.getValue(y - 1, x + 1)
+      val SE = area.getValue(y + 1, x + 1)
+      val SW = area.getValue(y + 1, x - 1)
+      val NW = area.getValue(y - 1, x - 1)
+
+      if      (NW == NE && SE == SW) { (NW == 'M' && SW == 'S') || (NW == 'S' && SW == 'M') }
+      else if (NW == SW && NE == SE) { (NW == 'M' && NE == 'S') || (NW == 'S' && NE == 'M') }
+      else false
+    }
+  }
+
+  private fun setup(lines: Sequence<String>, target: Char): Pair<List<Location>, List<List<Char>>> {
+    val locations = mutableListOf<Location>()
+    val area = lines.toList().mapIndexed { yIndex, line ->
+      line.mapIndexed { xIndex, letter ->
+        letter.also { if (it == target) { locations.add(Location(xIndex, yIndex)) } }
+      }
+    }
+
+    return locations to area
+  }
+}
+
+data class Location(val x: Int, val y: Int)
+
+private fun List<List<Char>>.findXMAS(y: Int, yDelta: Int, x: Int, xDelta: Int): String {
+  return (0..3)
+    .mapNotNull { delta -> this.getValue(y + (yDelta * delta), x + (xDelta * delta)) }
+    .joinToString("")
+}
+
+private fun List<List<Char>>.getValue(y: Int, x: Int): Char? {
+  return if (y in indices && x in this[y].indices) { this[y][x] } else { null }
+}

src/main/kotlin/me/peckb/aoc/_2024/calendar/day04/README.md

@@ -0,0 +1 @@
+## [Day 4: Ceres Search](https://adventofcode.com/2024/day/4)

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

@@ -3,6 +3,7 @@ package me.peckb.aoc._2024
 import dagger.Component
 import me.peckb.aoc._2024.calendar.day02.Day02Test
 import me.peckb.aoc._2024.calendar.day03.Day03Test
+import me.peckb.aoc._2024.calendar.day04.Day04Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -14,4 +15,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day01Test: Day01Test)
   fun inject(day02Test: Day02Test)
   fun inject(day03Test: Day03Test)
+  fun inject(day04Test: Day04Test)
 }

src/test/kotlin/me/peckb/aoc/_2024/calendar/day04/Day04Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2024.calendar.day04
+
+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 Day04Test {
+  @Inject
+  lateinit var day04: Day04
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay04PartOne() {
+    assertEquals(2639, day04.partOne(DAY_04))
+  }
+
+  @Test
+  fun testDay04PartTwo() {
+    assertEquals(2005, day04.partTwo(DAY_04))
+  }
+
+  companion object {
+    private const val DAY_04: String = "advent-of-code-input/2024/day04.input"
+  }
+}