Solve Day 12

2024/src/main/kotlin/aoc/year2024/Day12.kt

@@ -0,0 +1,70 @@
+package aoc.year2024
+
+import aoc.library.Direction
+import aoc.library.Point
+import aoc.library.Puzzle
+import aoc.library.move
+
+object Day12 : Puzzle<Int, Int>(12) {
+
+  override fun solvePart2(input: String): Int = solve(input, ::perimeterV2)
+
+  override fun solvePart1(input: String): Int = solve(input, ::perimeterV1)
+
+  private fun solve(
+    input: String,
+    perimeter: (Set<Point>) -> Int,
+  ): Int {
+    val garden = parse(input)
+    return clusterByRegions(garden).sumOf {
+      val pointsInRegion = it.points
+      perimeter(pointsInRegion) * pointsInRegion.size
+    }
+  }
+
+  private fun clusterByRegions(garden: Map<Point, Char>): List<Region> {
+    val regions = mutableListOf<Region>()
+    val visited = mutableSetOf<Point>()
+    garden.keys.forEach { start ->
+      if (start !in visited) {
+        val groupChar = garden.getValue(start)
+        val group = mutableSetOf<Point>()
+        fun visit(point: Point) {
+          if (!group.add(point)) return
+          point.adjacentOrthogonal()
+            .forEach { adjacent ->
+              val char = garden[adjacent]
+              if (char == groupChar) {
+                visit(adjacent)
+              }
+            }
+        }
+        visit(start)
+        regions += Region(groupChar, group)
+        visited.addAll(group)
+      }
+    }
+    return regions
+  }
+
+  private fun parse(input: String): Map<Point, Char> = input.lines().flatMapIndexed { y, line ->
+    line.mapIndexed { x, char ->
+      Point(x, y) to char
+    }
+  }.toMap()
+
+  private fun perimeterV1(points: Set<Point>): Int = points.sumOf { point ->
+    point.adjacentOrthogonal().count { it !in points }
+  }
+
+  private fun perimeterV2(points: Set<Point>): Int {
+    fun Point.hasFence(direction: Direction): Boolean = this in points && move(direction) !in points
+    return points.sumOf { point ->
+      Direction.entries.count { direction ->
+        point.hasFence(direction) && !point.move(direction.clockwise()).hasFence(direction)
+      }
+    }
+  }
+
+  private data class Region(val char: Char, val points: Set<Point>)
+}

2024/src/test/kotlin/aoc/year2024/Day12Test.kt

@@ -0,0 +1,79 @@
+package aoc.year2024
+
+import aoc.library.solvePart1
+import aoc.library.solvePart2
+import io.kotest.matchers.ints.shouldBeExactly
+import org.junit.jupiter.api.Test
+
+class Day12Test {
+
+  @Test
+  fun part1TestInput() {
+    Day12.solvePart1(
+      """
+    AAAA
+    BBCD
+    BBCC
+    EEEC
+      """.trimIndent(),
+    ) shouldBeExactly 140
+  }
+
+  @Test
+  fun part1TestInput2() {
+    Day12.solvePart1(
+      """
+    RRRRIICCFF
+    RRRRIICCCF
+    VVRRRCCFFF
+    VVRCCCJFFF
+    VVVVCJJCFE
+    VVIVCCJJEE
+    VVIIICJJEE
+    MIIIIIJJEE
+    MIIISIJEEE
+    MMMISSJEEE
+      """.trimIndent(),
+    ) shouldBeExactly 1930
+  }
+
+  @Test
+  fun part1() {
+    Day12.solvePart1() shouldBeExactly 1434856
+  }
+
+  @Test
+  fun part2TestInput() {
+    Day12.solvePart2(
+      """
+      AAAA
+      BBCD
+      BBCC
+      EEEC
+      """.trimIndent(),
+    ) shouldBeExactly 80
+  }
+
+  @Test
+  fun part2TestInput2() {
+    Day12.solvePart2(
+      """
+      RRRRIICCFF
+      RRRRIICCCF
+      VVRRRCCFFF
+      VVRCCCJFFF
+      VVVVCJJCFE
+      VVIVCCJJEE
+      VVIIICJJEE
+      MIIIIIJJEE
+      MIIISIJEEE
+      MMMISSJEEE
+      """.trimIndent(),
+    ) shouldBeExactly 1206
+  }
+
+  @Test
+  fun part2() {
+    Day12.solvePart2() shouldBeExactly 891106
+  }
+}