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Day 15
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‎src/main/kotlin/y24/Day14.kt

+4-6
Original file line numberDiff line numberDiff line change
@@ -18,14 +18,12 @@ class Day14(val input: Input, val rows: Int = 103, val cols: Int = 101) : Puzzle
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data class Robot(val p: Point, val v: Point)
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2020
private fun Robot.move(n: Int): Robot {
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var x = p.x + v.x * n
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while (x < 0) x += cols
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var y = p.y + v.y * n
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while (y < 0) y += rows
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val x = Math.floorMod(p.x + v.x * n, cols)
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val y = Math.floorMod(p.y + v.y * n, rows)
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return Robot(Point(
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col = x % cols,
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row = y % rows,
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col = x,
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row = y,
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), v)
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}
3129

‎src/main/kotlin/y24/Day15.kt

+179
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,179 @@
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package y24
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import common.puzzle.solvePuzzle
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import common.puzzle.Input
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import common.puzzle.Puzzle
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import common.datastructures.*
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import common.ext.*
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import common.util.*
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import java.util.*
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import kotlin.math.*
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import kotlin.system.exitProcess
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fun main() = solvePuzzle(year = 2024, day = 15) { Day15(it) }
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class Day15(val input: Input) : Puzzle {
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sealed class Tile {
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data object Wall : Tile()
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data class Box(val left: Boolean) : Tile()
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data object Empty : Tile()
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}
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data class Parsed(
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val grid: Grid<Tile>,
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val robot: Point,
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val moves: List<Dir>,
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)
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private fun parseInput(lines: List<String>): Parsed {
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val emptyLine = lines.indexOf("")
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var robot: Point? = null
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val grid = Grid(lines.subList(0, emptyLine)) { row, col, c ->
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when (c) {
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'#' -> Tile.Wall
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'.' -> Tile.Empty
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'@' -> {
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robot = Point(col, row)
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Tile.Empty
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}
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'O' -> Tile.Box(true)
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else -> error("unknown tile $c")
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}
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}
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val moves = lines.subList(emptyLine + 1, lines.size).flatMap {
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it.map { c ->
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when (c) {
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'<' -> directions[0]
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'^' -> directions[1]
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'>' -> directions[2]
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'v' -> directions[3]
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else -> error("unknown direction $c")
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}
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}
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}
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val r = robot ?: error("no robot found")
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return Parsed(grid, r, moves)
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}
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private fun tryMove(grid: Grid<Tile>, p: Point, dir: Dir): Boolean {
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val neigh = grid[p + dir.toPoint()]
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if (neigh.value == Tile.Wall) {
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return false
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}
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if (neigh.value is Tile.Box) {
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if (!tryMove(grid, neigh.toPoint(), dir)) {
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return false
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}
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}
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neigh.value = grid[p].value
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grid[p].value = Tile.Empty
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return true
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}
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private fun tryMove2(grid: Grid<Tile>, p: Point, dir: Dir): Boolean {
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if (!move2(grid, p, dir, dryRun = true)) {
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return false
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}
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return move2(grid, p, dir, dryRun = false)
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}
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private fun move2(grid: Grid<Tile>, p: Point, dir: Dir, dryRun: Boolean): Boolean {
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val toMove = when (val t = grid[p].value) {
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Tile.Empty -> listOf(p) // Robot
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Tile.Box(left = true) -> listOf(p + Point(1, 0), p)
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Tile.Box(left = false) -> listOf(p + Point(-1, 0), p)
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else -> error("unexpected tile $t")
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}
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return toMove.all { point ->
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val neigh = grid[point + dir.toPoint()]
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if (neigh.value == Tile.Wall) {
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return@all false
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}
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if (neigh.value is Tile.Box) {
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val neighIsLeftBox = (neigh.value as Tile.Box).left
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// Prevent recursion, this is the left side pushing into the right side to the right (or vice versa).
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// We will already check this move as part of the right side of the box.
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val skip = (dir == Dir(0, 1) && !neighIsLeftBox) ||
106+
(dir == Dir(0, -1) && neighIsLeftBox)
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if (!skip && !move2(grid, neigh.toPoint(), dir, dryRun)) {
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return@all false
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}
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}
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if (dryRun) {
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return@all true
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}
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neigh.value = grid[point].value
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grid[point].value = Tile.Empty
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return@all true
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}
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}
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private fun expand(grid: Grid<Tile>): Grid<Tile> {
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return Grid(rows = grid.numRows, cols = grid.numCols * 2) { row, col ->
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val v = grid[row][col / 2].value
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if (v is Tile.Box) {
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v.copy(left = col % 2 == 0)
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} else {
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v
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}
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}
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}
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private fun Grid<Tile>.gpsSum(): Int {
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return cells().sumOf { (row, col, value) ->
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when (value) {
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Tile.Box(true) -> 100 * row + col
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else -> 0
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}
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}
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}
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override fun solveLevel1(): Any {
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val (grid, robotInitial, moves) = parseInput(input.lines)
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var robot = robotInitial
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moves.forEach { dir ->
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if (tryMove(grid, robot, dir)) {
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robot += dir.toPoint()
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}
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}
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return grid.gpsSum()
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}
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override fun solveLevel2(): Any {
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val (grid, robotInitial, moves) = parseInput(input.lines)
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val expandedGrid = expand(grid)
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var robot = robotInitial.copy(col = robotInitial.col * 2)
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moves.forEach { dir ->
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if (tryMove2(expandedGrid, robot, dir)) {
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robot += dir.toPoint()
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}
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expandedGrid.cellFormatter = Grid.CellFormatter({ cell ->
165+
if (cell.toPoint() == robot) return@CellFormatter "@"
166+
when (cell.value) {
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Tile.Wall -> "#"
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Tile.Empty -> "."
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Tile.Box(true) -> "["
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Tile.Box(false) -> "]"
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else -> error("")
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}
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}, "")
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// println(expandedGrid)
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}
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return expandedGrid.gpsSum()
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}
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}

‎src/test/kotlin/y24/Day15Test.kt

+43
Original file line numberDiff line numberDiff line change
@@ -0,0 +1,43 @@
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package y24
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import common.puzzle.Input
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import org.junit.jupiter.api.Assertions.assertEquals
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import org.junit.jupiter.api.Test
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internal class Day15Test {
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private val sample = Input("""
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##########
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#..O..O.O#
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#......O.#
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#.OO..O.O#
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#[email protected].#
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#O#..O...#
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#O..O..O.#
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#.OO.O.OO#
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#....O...#
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##########
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<vv>^<v^>v>^vv^v>v<>v^v<v<^vv<<<^><<><>>v<vvv<>^v^>^<<<><<v<<<v^vv^v>^
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vvv<<^>^v^^><<>>><>^<<><^vv^^<>vvv<>><^^v>^>vv<>v<<<<v<^v>^<^^>>>^<v<v
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><>vv>v^v^<>><>>>><^^>vv>v<^^^>>v^v^<^^>v^^>v^<^v>v<>>v^v^<v>v^^<^^vv<
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<<v<^>>^^^^>>>v^<>vvv^><v<<<>^^^vv^<vvv>^>v<^^^^v<>^>vvvv><>>v^<<^^^^^
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^><^><>>><>^^<<^^v>>><^<v>^<vv>>v>>>^v><>^v><<<<v>>v<v<v>vvv>^<><<>^><
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^>><>^v<><^vvv<^^<><v<<<<<><^v<<<><<<^^<v<^^^><^>>^<v^><<<^>>^v<v^v<v^
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>^>>^v>vv>^<<^v<>><<><<v<<v><>v<^vv<<<>^^v^>^^>>><<^v>>v^v><^^>>^<>vv^
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<><^^>^^^<><vvvvv^v<v<<>^v<v>v<<^><<><<><<<^^<<<^<<>><<><^^^>^^<>^>v<>
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^^>vv<^v^v<vv>^<><v<^v>^^^>>>^^vvv^>vvv<>>>^<^>>>>>^<<^v>^vvv<>^<><<v>
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v^^>>><<^^<>>^v^<v^vv<>v^<<>^<^v^v><^<<<><<^<v><v<>vv>>v><v^<vv<>v^<<^
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""".trimIndent())
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private val day = Day15(sample)
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@Test
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fun solveLevel1() {
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assertEquals(10092, day.solveLevel1())
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}
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@Test
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fun solveLevel2() {
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assertEquals(9021, day.solveLevel2())
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}
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}

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