day(20): add solution
Signed-off-by: Matej Focko <mfocko@redhat.com>
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77
src/year2021/day20/Day20.kt
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77
src/year2021/day20/Day20.kt
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package year2021.day20
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import readInput
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data class Point(val x: Int, val y: Int)
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fun getSquare(pixel: Point): Iterable<Point> =
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(pixel.y - 1..pixel.y + 1).flatMap { y -> (pixel.x - 1..pixel.x + 1).map { x -> Point(x, y) } }
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data class TrenchMap(
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val algorithm: List<Char>,
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val map: Map<Point, Char>,
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val default: Char = '.'
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) {
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fun get(key: Point): Char = map.getOrDefault(key, default)
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fun get(x: Int, y: Int): Char = get(Point(x, y))
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private val xs: IntRange
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get() = (map.keys.minOf { it.x } - 2..map.keys.maxOf { it.x } + 2)
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private val ys: IntRange
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get() = (map.keys.minOf { it.y } - 2..map.keys.maxOf { it.y } + 2)
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private val indices: Iterable<Point>
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get() = ys.flatMap { y -> xs.map { x -> Point(x, y) } }
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fun print() {
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for (y in ys) {
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for (x in xs) {
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print(get(x, y))
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}
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println()
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}
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}
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private fun toIndex(square: Iterable<Point>): Int =
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square.map { if (get(it) == '#') 1 else 0 }.fold(0) { acc, bit -> acc * 2 + bit }
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private fun enhancePixel(pixel: Point): Char = algorithm[toIndex(getSquare(pixel))]
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fun enhance(): TrenchMap =
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TrenchMap(
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algorithm,
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indices.associateWith { enhancePixel(it) },
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when (default) {
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'.' -> algorithm.first()
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'#' -> algorithm.last()
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else -> error("Invalid char found")
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}
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)
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}
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fun List<String>.toTrenchMap(): TrenchMap =
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TrenchMap(
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this.first().toList(),
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this.drop(2)
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.flatMapIndexed { y, row ->
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row.mapIndexed { x, cell -> Point(x, y) to cell }
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}.toMap()
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)
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fun part1(input: TrenchMap): Int =
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(1..2).fold(input) { acc, i -> acc.enhance() }.map.values.count { it == '#' }
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fun part2(input: TrenchMap): Int =
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(1..50).fold(input) { acc, i -> acc.enhance() }.map.values.count { it == '#' }
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fun main() {
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val sample = readInput(20, "sample").toTrenchMap()
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val input = readInput(20, "input").toTrenchMap()
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check(part1(sample) == 35)
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println(part1(input))
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check(part2(sample) == 3351)
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println(part2(input))
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}
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7
src/year2021/day20/sample.txt
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7
src/year2021/day20/sample.txt
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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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