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Day 12 2024 (#271)
* Day 12 2024
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‎src/main/kotlin/me/peckb/aoc/_2024/calendar/day12/Day12.kt‎

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package me.peckb.aoc._2024.calendar.day12
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import javax.inject.Inject
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import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
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import java.util.LinkedList
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import java.util.Queue
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class Day12 @Inject constructor(
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private val generatorFactory: InputGeneratorFactory,
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) {
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fun partOne(filename: String) = generatorFactory.forFile(filename).read { input ->
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val (_, fields) = createFields(input)
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fields.sumOf { field -> field.perimeter * field.crops.size }
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}
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fun partTwo(filename: String) = generatorFactory.forFile(filename).read { input ->
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val (area, knownFields) = createFields(input)
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// setup empty map
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val largeArea = mutableListOf<MutableList<Char>>()
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val height = area.size + 4
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val width = area[0].size + 4
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repeat(height) { largeArea.add(mutableListOf<Char>().apply { repeat(width) { add('.') } }) }
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knownFields.forEach { field ->
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field.crops.forEach { c -> largeArea[c.y + 2][c.x + 2] = c.type }
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field.crops.forEach { c ->
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if (c.onPerimeter) {
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val n = (c.y + 2) - 1 to (c.x + 2)
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val s = (c.y + 2) + 1 to (c.x + 2)
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val e = (c.y + 2) to (c.x + 2) + 1
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val w = (c.y + 2) to (c.x + 2) - 1
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// if the given neighbor matches, put an "edge" on the marker
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listOf(n, s, e, w).forEach { (y, x) -> if (largeArea[y][x] != c.type) { largeArea[y][x] = '+' } }
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}
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}
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// sweep for the sides going left to right
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field.doSweep(
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firstLoopSize = largeArea.size,
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secondLoopSize = largeArea[0].size,
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item = { y: Int, x: Int -> largeArea[y][x] },
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n1 = { y: Int, x: Int -> largeArea[y - 1][x] },
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n2 = { y: Int, x: Int -> largeArea[y + 1][x] },
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)
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// sweep for the sides going top to bottom
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field.doSweep(
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firstLoopSize = largeArea[0].size,
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secondLoopSize = largeArea.size,
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item = { x: Int, y: Int -> largeArea[y][x] },
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n1 = { x: Int, y: Int -> largeArea[y][x - 1] },
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n2 = { x: Int, y: Int -> largeArea[y][x + 1] },
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)
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// reset the map
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repeat(largeArea.size) { y -> repeat(largeArea[y].size) { x -> largeArea[y][x] = '.' } }
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}
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knownFields.sumOf { field -> field.sides * field.crops.size}
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}
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private fun createFields(input: Sequence<String>): Pair<MutableList<MutableList<Crop>>, MutableList<Field>> {
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val area = mutableListOf<MutableList<Crop>>()
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val unKnownCrops = mutableSetOf<Crop>()
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val knownFields = mutableListOf<Field>()
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input.forEachIndexed { yIndex, line ->
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val row = mutableListOf<Crop>()
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line.forEachIndexed { xIndex, char ->
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val crop = Crop(char, yIndex, xIndex)
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row.add(crop)
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unKnownCrops.add(crop)
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}
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area.add(row)
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}
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while (unKnownCrops.isNotEmpty()) {
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val nextAreaNodes: Queue<Crop> = LinkedList()
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nextAreaNodes.add(unKnownCrops.first())
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val field = Field()
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loop@ while(nextAreaNodes.isNotEmpty()) {
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val c = nextAreaNodes.remove()
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if (field.crops.contains(c)) { continue@loop }
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unKnownCrops.remove(c)
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field.crops.add(c)
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val n = area.get(c.y - 1, c.x)
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val s = area.get(c.y + 1, c.x)
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val e = area.get(c.y, c.x + 1)
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val w = area.get(c.y, c.x - 1)
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listOf(n, s, e, w).forEach { neighbor: Crop? ->
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if (neighbor == null) {
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field.perimeter++
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c.onPerimeter = true
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} else {
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if (neighbor.type == c.type) {
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nextAreaNodes.add(neighbor)
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} else {
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field.perimeter++
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c.onPerimeter = true
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}
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}
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}
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}
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knownFields.add(field)
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}
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return area to knownFields
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}
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private fun Field.doSweep(
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firstLoopSize: Int,
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secondLoopSize: Int,
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item: (Int, Int) -> Char,
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n1: (Int, Int) -> Char,
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n2: (Int, Int) -> Char,
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) {
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val fieldType = crops.first().type
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// loop starting in one direction
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repeat(firstLoopSize) { f ->
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var n1SideFound = false
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var n2SideFound = false
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// for that direction, iterate through the other
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repeat(secondLoopSize) { s ->
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// if we found an "edge"
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if (item(f, s) == '+') {
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// check the first neighbor (ignoring the direction of travel)
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val n1Char = n1(f, s)
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if (n1Char == fieldType) {
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// if the neighbor matches our type, this is a side, track it if we weren't
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if (!n1SideFound) {
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n1SideFound = true
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}
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} else if (n1SideFound) {
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// if the neighbor wasn't our type; but we were tracking, we found the full side
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n1SideFound = false
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sides++
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}
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// check the second neighbor (ignoring the direction of travel)
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val n2Char = n2(f, s)
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if (n2Char == fieldType) {
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// if the neighbor matches our type, this is a side, track it if we weren't
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if (!n2SideFound) {
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n2SideFound = true
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}
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} else if (n2SideFound) {
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// if the neighbor wasn't our type; but we were tracking, we found the full side
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n2SideFound = false
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sides++
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}
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} else {
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if (n1SideFound) {
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// if the item wasn't a wall, and we were tracking, we found the full side
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n1SideFound = false
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sides++
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}
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if (n2SideFound) {
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// if the item wasn't a wall, and we were tracking, we found the full side
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n2SideFound = false
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sides++
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}
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}
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}
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}
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}
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}
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private fun MutableList<MutableList<Crop>>.get(y: Int, x: Int): Crop? {
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return if (y in indices && x in this[y].indices) { this[y][x] } else { null }
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}
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data class Crop(val type: Char, val y: Int, val x: Int) {
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var onPerimeter = false
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}
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data class Field(val crops: MutableSet<Crop> = mutableSetOf(), var perimeter: Long = 0L) {
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var sides = 0L
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}

‎src/main/kotlin/me/peckb/aoc/_2024/calendar/day12/README.md‎

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## [Day 12: Garden Groups](https://adventofcode.com/2024/day/12)

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

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import me.peckb.aoc._2024.calendar.day09.Day09Test
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import me.peckb.aoc._2024.calendar.day10.Day10Test
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import me.peckb.aoc._2024.calendar.day11.Day11Test
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import me.peckb.aoc._2024.calendar.day12.Day12Test
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import javax.inject.Singleton
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import me.peckb.aoc.DayComponent
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import me.peckb.aoc.InputModule
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fun inject(day09Test: Day09Test)
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fun inject(day10Test: Day10Test)
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fun inject(day11Test: Day11Test)
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fun inject(day12Test: Day12Test)
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}

‎src/test/kotlin/me/peckb/aoc/_2024/calendar/day12/Day12Test.kt‎

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package me.peckb.aoc._2024.calendar.day12
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import javax.inject.Inject
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import me.peckb.aoc._2024.DaggerTestDayComponent
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import org.junit.jupiter.api.Assertions.assertEquals
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import org.junit.jupiter.api.BeforeEach
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import org.junit.jupiter.api.Test
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internal class Day12Test {
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@Inject
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lateinit var day12: Day12
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@BeforeEach
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fun setup() {
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DaggerTestDayComponent.create().inject(this)
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}
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@Test
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fun testDay12PartOne() {
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assertEquals(1446042, day12.partOne(DAY_12))
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}
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@Test
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fun testDay12PartTwo() {
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assertEquals(902742, day12.partTwo(DAY_12))
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}
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companion object {
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private const val DAY_12: String = "advent-of-code-input/2024/day12.input"
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}
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}

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