Day -07 2025

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2025/calendar/day07/Day07.kt

@@ -0,0 +1,86 @@
+package me.peckb.aoc._2025.calendar.day07
+
+import javax.inject.Inject
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+import kotlin.text.indexOf
+import kotlin.text.toCharArray
+
+class Day07 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).read { input ->
+    var beamIndices = mutableSetOf<Int>()
+    val manifold = mutableListOf<MutableList<Char>>()
+
+    input.forEachIndexed { index, line ->
+      if (index == 0) beamIndices.add(line.indexOf('S'))
+      manifold.add(line.toCharArray().toMutableList())
+    }
+
+    var depth = 1
+    var splits = 0
+    while (depth < manifold.size) {
+      val updateBeamIndices = mutableSetOf<Int>()
+      val line = manifold[depth]
+
+      beamIndices.forEach { beamIndex ->
+        if (line[beamIndex] == '^') {
+          splits++
+          updateBeamIndices.add(beamIndex - 1)
+          updateBeamIndices.add(beamIndex + 1)
+        } else {
+          updateBeamIndices.add(beamIndex)
+        }
+      }
+
+      beamIndices = updateBeamIndices
+      depth++
+    }
+
+    splits
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).read { input ->
+    var beams = mutableMapOf<Location, Long>()
+    val manifold = mutableListOf<MutableList<Char>>()
+
+    input.forEachIndexed { index, line ->
+      if (index == 0) {
+        beams[Location(0, line.indexOf('S'))] = 1
+      }
+      manifold.add(line.toCharArray().toMutableList())
+    }
+
+    var depth = 1
+    while (depth < manifold.size) {
+      val newBeams = mutableMapOf<Location, Long>().withDefault { 0 }
+      val line = manifold[depth]
+
+      beams.forEach { (location, count) ->
+        if (location.depth != depth - 1) { throw IllegalStateException("We should only be tracking the last row.") }
+
+        if (line[location.index] == '^') {
+          val left = Location(depth, location.index - 1)
+          val right = Location(depth, location.index + 1)
+
+          newBeams[left] = newBeams.getValue(left) + count
+          newBeams[right] = newBeams.getValue(right) + count
+        } else {
+          val below = Location(depth, location.index)
+          newBeams[below] = newBeams.getValue(below) + count
+        }
+      }
+
+      beams = newBeams
+      depth++
+    }
+
+    beams.values.sum()
+  }
+}
+
+data class Location(val depth: Int, val index: Int) {
+  override fun toString(): String {
+    return "($depth,$index)"
+  }
+}

src/main/kotlin/me/peckb/aoc/_2025/calendar/day07/README.md

@@ -0,0 +1 @@
+## [](https://adventofcode.com/2025/day/7)

src/test/kotlin/me/peckb/aoc/_2025/TestDayComponent.kt

@@ -6,6 +6,7 @@ import me.peckb.aoc._2025.calendar.day03.Day03Test
 import me.peckb.aoc._2025.calendar.day04.Day04Test
 import me.peckb.aoc._2025.calendar.day05.Day05Test
 import me.peckb.aoc._2025.calendar.day06.Day06Test
+import me.peckb.aoc._2025.calendar.day07.Day07Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -20,4 +21,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day04Test: Day04Test)
   fun inject(day05Test: Day05Test)
   fun inject(day06Test: Day06Test)
+  fun inject(day07Test: Day07Test)
 }

src/test/kotlin/me/peckb/aoc/_2025/calendar/day07/Day07Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2025.calendar.day07
+
+import javax.inject.Inject
+
+import me.peckb.aoc._2025.DaggerTestDayComponent
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.BeforeEach
+import org.junit.jupiter.api.Test
+
+internal class Day07Test {
+  @Inject
+  lateinit var day07: Day07
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay07PartOne() {
+    assertEquals(1550, day07.partOne(DAY_07))
+  }
+
+  @Test
+  fun testDay07PartTwo() {
+    assertEquals(9897897326778, day07.partTwo(DAY_07))
+  }
+
+  companion object {
+    private const val DAY_07: String = "advent-of-code-input/2025/day07.input"
+  }
+}