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Day 16 2024 (#277)
* Day 16 2024
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‎src/main/kotlin/me/peckb/aoc/_2024/calendar/day16/Day16.kt‎

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package me.peckb.aoc._2024.calendar.day16
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import me.peckb.aoc._2024.calendar.day16.Direction.E
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import me.peckb.aoc._2024.calendar.day16.Direction.N
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import me.peckb.aoc._2024.calendar.day16.Direction.S
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import me.peckb.aoc._2024.calendar.day16.Direction.W
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import javax.inject.Inject
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import me.peckb.aoc.generators.InputGenerator.InputGeneratorFactory
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import me.peckb.aoc.pathing.Dijkstra
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import me.peckb.aoc.pathing.DijkstraNodeWithCost
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import java.util.PriorityQueue
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class Day16 @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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lateinit var start: Room
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lateinit var end: Room
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val maze = mutableListOf<MutableList<Room>>()
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input.forEachIndexed { y, line ->
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val row = mutableListOf<Room>()
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line.forEachIndexed { x, c ->
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when (c) {
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'#' -> row.add(Room(y, x, space = Space.FULL))
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'.' -> row.add(Room(y, x))
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'S' -> row.add(Room(y, x).also { start = it; it.direction = E })
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'E' -> row.add(Room(y, x).also { end = it })
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}
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}
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maze.add(row)
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}
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val solver = MazeDijkstra(maze)
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val solutions = solver.solve(start)
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solutions[end]
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}
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fun partTwo(filename: String) = generatorFactory.forFile(filename).read { input ->
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lateinit var start: Pair<Int, Int>
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lateinit var end: Pair<Int, Int>
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val maze = mutableListOf<MutableList<Space>>()
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input.forEachIndexed { y, line ->
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val row = mutableListOf<Space>()
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line.forEachIndexed { x, c ->
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when (c) {
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'#' -> row.add(Space.FULL)
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'.' -> row.add(Space.EMPTY)
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'S' -> row.add(Space.EMPTY.also { start = y to x } )
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'E' -> row.add(Space.EMPTY.also { end = y to x } )
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}
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}
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maze.add(row)
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}
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val visitedWithCheapestCost = mutableMapOf<Triple<Int, Int, Direction>, Long>()
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val visited = mutableSetOf<SpaceWithPath>()
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val toVisit = PriorityQueue<SpaceWithPath>()
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toVisit.add(SpaceWithPath(start, end, listOf(start)))
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loop@ while(toVisit.isNotEmpty()) {
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val current = toVisit.poll()
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if (current.loc == end) {
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visited.add(current)
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continue@loop
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}
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val myDirection = SpaceWithPath.findDirection(current.path)
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val key = Triple(current.loc.first, current.loc.second, myDirection)
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if (visitedWithCheapestCost.getOrDefault(key, Long.MAX_VALUE) < current.cost) {
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continue@loop
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} else {
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visitedWithCheapestCost[key] = current.cost
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}
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val n = (-1 to 0)
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val e = (0 to 1)
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val s = (1 to 0)
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val w = (0 to -1)
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listOf(n, s, e, w)
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.asSequence()
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.map { (yDelta, xDelta) ->
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current.loc.first + yDelta to current.loc.second + xDelta
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}
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.filter { (y, x) ->
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y in maze.indices && x in maze[y].indices && maze[y][x] == Space.EMPTY && !current.path.contains(y to x)
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}
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.forEach { (y, x) ->
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toVisit.add(SpaceWithPath(y to x, end, current.path.plus(y to x)))
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}
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}
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val minCostRoutes = visited.filter { it.loc == end }.groupBy { (_, _, path, cost) ->
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cost
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}.minBy { it.key }
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minCostRoutes.value.fold(mutableSetOf<Pair<Int, Int>>()) { acc, next ->
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acc.also { it.addAll(next.path) }
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}.size
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}
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data class SpaceWithCost(
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val loc: Pair<Int, Int>,
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val cost: Long
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)
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data class SpaceWithPath(
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val loc: Pair<Int, Int>,
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val end: Pair<Int, Int>,
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val path: List<Pair<Int, Int>>,
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val cost: Long = findCost(path)
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) : Comparable<SpaceWithPath> {
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override fun compareTo(other: SpaceWithPath): Int = cost.compareTo(other.cost)
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companion object {
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fun findDirection(path: List<Pair<Int, Int>>): Direction {
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var direction = E
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path.windowed(2).lastOrNull()?.let { (s, d) ->
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val deltas = (d.first - s.first) to (d.second - s.second)
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direction = when (deltas) {
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(-1 to 0) -> N
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(0 to 1) -> E
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(1 to 0) -> S
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(0 to -1) -> W
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else -> throw IllegalStateException("Unknown Deltas: $deltas")
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}
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}
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return direction
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}
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fun findCost(path: List<Pair<Int, Int>>): Long {
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var direction = E
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return path.windowed(2).sumOf { (s, d) ->
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val deltas = (d.first - s.first) to (d.second - s.second)
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val newDirection = when (deltas) {
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(-1 to 0) -> N
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(0 to 1) -> E
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(1 to 0) -> S
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(0 to -1) -> W
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else -> throw IllegalStateException("Unknown Deltas: $deltas")
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}
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(direction.turns(newDirection) + 1).also { direction = newDirection }
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}
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}
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}
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}
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}
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class MazeDijkstra(private val maze: MutableList<MutableList<Room>>) : Dijkstra<Room, Long, RoomWithCost> {
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override fun Room.withCost(cost: Long) = RoomWithCost(this, cost).withMaze(maze)
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override fun Long.plus(cost: Long) = this + cost
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override fun maxCost() = Long.MAX_VALUE
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override fun minCost() = 0L
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}
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data class RoomWithCost(val room: Room, val cost: Long) : DijkstraNodeWithCost<Room, Long> {
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private lateinit var maze: MutableList<MutableList<Room>>
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fun withMaze(maze: MutableList<MutableList<Room>>) = apply { this.maze = maze }
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override fun compareTo(other: DijkstraNodeWithCost<Room, Long>): Int = cost.compareTo(other.cost())
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override fun neighbors(): List<DijkstraNodeWithCost<Room, Long>> {
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val myDirection = room.direction
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val n = (-1 to 0) to Direction.N
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val e = (0 to 1) to E
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val s = (1 to 0) to Direction.S
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val w = (0 to -1) to Direction.W
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return listOf(n, s, e, w).mapNotNull { (loc, dir) ->
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val (y, x) = room.y + loc.first to room.x + loc.second
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if (y !in maze.indices || x !in maze[y].indices) { null }
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else if (maze[y][x].space == Space.FULL) { null }
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else {
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val cost = myDirection.turns(dir) + 1
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RoomWithCost(Room(y, x).also { it.direction = dir }, cost).withMaze(maze)
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}
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}
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}
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override fun node(): Room = room
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override fun cost(): Long = cost
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companion object {
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private const val TURN_COST = 1000
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}
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}
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data class Room(
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val y: Int,
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val x: Int,
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val space: Space = Space.EMPTY
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) {
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var direction: Direction? = null
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}
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enum class Space { FULL, EMPTY }
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enum class Direction { N, E, S, W }
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private fun Direction?.turns(direction: Direction): Long {
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if (this == null) return 0
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if (this == direction) return 0
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if (this == Direction.N && direction == Direction.S ||
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this == Direction.S && direction == Direction.N ||
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this == E && direction == Direction.W ||
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this == Direction.W && direction == E
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) return 2000
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return 1000
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}

‎src/main/kotlin/me/peckb/aoc/_2024/calendar/day16/README.md‎

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## [Day 16: Reindeer Maze](https://adventofcode.com/2024/day/16)

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

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import me.peckb.aoc._2024.calendar.day13.Day13Test
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import me.peckb.aoc._2024.calendar.day14.Day14Test
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import me.peckb.aoc._2024.calendar.day15.Day15Test
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import me.peckb.aoc._2024.calendar.day16.Day16Test
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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(day13Test: Day13Test)
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fun inject(day14Test: Day14Test)
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fun inject(day15Test: Day15Test)
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fun inject(day16Test: Day16Test)
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}

‎src/test/kotlin/me/peckb/aoc/_2024/calendar/day16/Day16Test.kt‎

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package me.peckb.aoc._2024.calendar.day16
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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 Day16Test {
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@Inject
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lateinit var day16: Day16
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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 testDay16PartOne() {
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assertEquals(66404, day16.partOne(DAY_16))
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}
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@Test
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fun testDay16PartTwo() {
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assertEquals(433, day16.partTwo(DAY_16))
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}
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companion object {
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private const val DAY_16: String = "advent-of-code-input/2024/day16.input"
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}
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}

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