Day 09 2025 (#303)

* Day 09 2025

* Sorting by size and finding the first that fits

Author: peckb1

src/main/kotlin/me/peckb/aoc/_2025/calendar/day09/Day09.kt

@@ -0,0 +1,65 @@
+package me.peckb.aoc._2025.calendar.day09
+
+import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
+import org.apache.commons.math3.geometry.euclidean.twod.PolygonsSet
+import org.apache.commons.math3.geometry.euclidean.twod.Vector2D
+import org.apache.commons.math3.geometry.euclidean.twod.hull.ConvexHullGenerator2D
+import org.apache.commons.math3.geometry.euclidean.twod.hull.MonotoneChain
+import javax.inject.Inject
+import kotlin.math.abs
+import kotlin.math.max
+
+
+class Day09 @Inject constructor(
+  private val generatorFactory: InputGeneratorFactory,
+) {
+  fun partOne(filename: String) = generatorFactory.forFile(filename).readAs(::day09) { redTileLocations ->
+    val tiles = redTileLocations.toList()
+
+    var largestArea = -1.0
+
+    tiles.indices.forEach { ti1 ->
+      ((ti1 + 1) until tiles.size).forEach { ti2 ->
+        val t1 = tiles[ti1]
+        val t2 = tiles[ti2]
+
+        val area = (abs(t1.x - t2.x) + 1) * (abs(t1.y - t2.y) + 1)
+
+        largestArea = max(largestArea, area)
+      }
+    }
+
+    largestArea.toLong()
+  }
+
+  fun partTwo(filename: String) = generatorFactory.forFile(filename).readAs(::day09) { input ->
+    val vertices = input.map { Vector2D(it.x, it.y) }.toList()
+    val polygonSet = PolygonsSet(1e-3, *vertices.toTypedArray())
+    val hullGenerator: ConvexHullGenerator2D = MonotoneChain()
+
+    val areas = mutableListOf<Pair<Long, List<Vector2D>>>()
+
+    vertices.indices.forEach { ti1 ->
+      ((ti1 + 1) until vertices.size).forEach { ti2 ->
+        val t1 = vertices[ti1]
+        val t2 = vertices[ti2]
+
+        if (t1.x == t2.x || t1.y == t2.y) { return@forEach }
+
+        val size = ((abs(t1.x - t2.x) + 1) * (abs(t1.y - t2.y) + 1)).toLong()
+        val i1 = Vector2D(t1.x, t2.y)
+        val i2 = Vector2D(t2.x, t1.y)
+
+        areas.add(size to listOf(t1, i1, t2, i2))
+      }
+    }
+
+    areas.sortedByDescending { it.first }.first { (_, vertices) ->
+      polygonSet.contains(hullGenerator.generate(vertices).createRegion())
+    }.first
+  }
+
+  private fun day09(line: String) = line.split(",").map { it.toDouble() }.let { (x, y) -> Location(x, y) }
+}
+
+data class Location(val x: Double, val y: Double)

src/main/kotlin/me/peckb/aoc/_2025/calendar/day09/README.md

@@ -0,0 +1 @@
+## [Day 9: Movie Theater](https://adventofcode.com/2025/day/9)

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

@@ -8,6 +8,7 @@ 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 me.peckb.aoc._2025.calendar.day08.Day08Test
+import me.peckb.aoc._2025.calendar.day09.Day09Test
 import javax.inject.Singleton
 import me.peckb.aoc.DayComponent
 import me.peckb.aoc.InputModule
@@ -24,4 +25,5 @@ internal interface TestDayComponent : DayComponent {
   fun inject(day06Test: Day06Test)
   fun inject(day07Test: Day07Test)
   fun inject(day08Test: Day08Test)
+  fun inject(day09Test: Day09Test)
 }

src/test/kotlin/me/peckb/aoc/_2025/calendar/day09/Day09Test.kt

@@ -0,0 +1,32 @@
+package me.peckb.aoc._2025.calendar.day09
+
+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 Day09Test {
+  @Inject
+  lateinit var day09: Day09
+
+  @BeforeEach
+  fun setup() {
+    DaggerTestDayComponent.create().inject(this)
+  }
+
+  @Test
+  fun testDay09PartOne() {
+    assertEquals(4749929916, day09.partOne(DAY_09))
+  }
+
+  @Test
+  fun testDay09PartTwo() {
+    assertEquals(1572047142, day09.partTwo(DAY_09))
+  }
+
+  companion object {
+    private const val DAY_09: String = "advent-of-code-input/2025/day09.input"
+  }
+}