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object Day25 {
private class SeaCucumbers(private val width: Int, private val height: Int, private val matrix: Array<SeaTile>) {
companion object {
fun fromLines(lines: List<String>) =
Pos2D(
lines.getOrNull(0)?.length ?: throw IllegalArgumentException("Sea must have a non-zero height!"),
lines.size
).let { size ->
SeaCucumbers(size.x, size.y, Array(size.x * size.y) {
when (val char = lines[it / size.x][it % size.x]) {
'>' -> SeaTile.Cucumber.EastFacing
'v' -> SeaTile.Cucumber.SouthFacing
'.' -> SeaTile.EmptyTile
else -> throw IllegalArgumentException("Found '$char', expected '>', 'v' or '.'!")
}
})
}
}
private sealed class SeaTile {
object EmptyTile : SeaTile()
sealed class Cucumber : SeaTile() {
object EastFacing : Cucumber()
object SouthFacing : Cucumber()
}
}
private fun moveIndex(index: Int, offset: Pos2D) =
((index / width + offset.y) % height) * width + (index + offset.x) % width
private inline fun <reified T : SeaTile.Cucumber> stepDirection(pos: Pos2D) {
matrix
.asSequence()
.withIndex()
.map { (index, seaTile) ->
val nextIndex = moveIndex(index, pos)
if (seaTile is T && matrix[nextIndex] is SeaTile.EmptyTile) {
index to nextIndex
} else {
null
}
}
.filterNotNull()
.toList()
.forEach { (index, nextIndex) ->
matrix[nextIndex] = matrix[index].also { matrix[index] = SeaTile.EmptyTile }
}
}
private fun stepOnce() {
stepDirection<SeaTile.Cucumber.EastFacing>(Pos2D(1, 0))
stepDirection<SeaTile.Cucumber.SouthFacing>(Pos2D(0, 1))
}
fun simulate(): Int {
var count = 0
do {
val previousHashCode = matrix.contentHashCode()
stepOnce()
count++
} while (matrix.contentHashCode() != previousHashCode)
return count
}
override fun toString(): String = matrix
.withIndex()
.joinToString("") { (index, seaTile) ->
when (seaTile) {
SeaTile.Cucumber.EastFacing -> ">"
SeaTile.Cucumber.SouthFacing -> "v"
SeaTile.EmptyTile -> "."
} + (if (index % width == width - 1) "\n" else "")
}
}
fun singlePart(input: List<String>) = SeaCucumbers.fromLines(input).simulate()
}
fun main() {
val testInput = readInputAsLines("Day25_test")
check(Day25.singlePart(testInput) == 58)
val input = readInputAsLines("Day25")
println(Day25.singlePart(input))
}
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