1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
|
object Day20 {
private class Enhancement private constructor(
private val algorithm: BooleanArray,
private val initialImage: Set<Pos2D>
) {
companion object {
fun fromString(string: String) = string.split("\n\n").let { (algorithm, image) ->
Enhancement(
algorithm.map { it == '#' }.toBooleanArray(),
image
.split("\n")
.withIndex()
.flatMap { (y, row) ->
row.withIndex().mapNotNull { (x, char) -> if (char == '#') Pos2D(x, y) else null }
}
.toSet()
)
}
}
private fun nextStateFor(currentImage: Set<Pos2D>, pos: Pos2D) = combinations(1 downTo -1)
.map { (dy, dx) -> if (currentImage.contains(pos + Pos2D(dx, dy))) 1 else 0 }
.withIndex()
.sumOf { (index, value) -> value shl index }
.let { algorithm[it] }
fun enhance(times: Int): Int {
return generateSequence(StepState.initial(initialImage)) { (image, topLeft, bottomRight) ->
StepState(
combinations(topLeft.y..bottomRight.y, topLeft.x..bottomRight.x)
.mapNotNull { (y, x) ->
Pos2D(x, y).let { if (nextStateFor(image, it)) it else null }
}.toSet(),
topLeft + Pos2D(1, 1),
bottomRight - Pos2D(1, 1)
)
}.drop(times).first().image.size
}
}
private data class StepState(val image: Set<Pos2D>, val topLeft: Pos2D, val bottomRight: Pos2D) {
companion object {
fun initial(image: Set<Pos2D>) = StepState(image, Pos2D(-100, -100), Pos2D(200, 200))
}
}
fun part1(input: String) = Enhancement.fromString(input).enhance(2)
fun part2(input: String) = Enhancement.fromString(input).enhance(50)
}
fun main() {
val testInput = readInputAsString("Day20_test")
check(Day20.part1(testInput) == 35)
check(Day20.part2(testInput) == 3351)
val input = readInputAsString("Day20")
println(Day20.part1(input))
println(Day20.part2(input))
}
|
