diff --git a/day5/day5.kt b/day5/day5.kt new file mode 100644 index 0000000..234d883 --- /dev/null +++ b/day5/day5.kt @@ -0,0 +1,165 @@ +import java.io.File + +typealias Map = Pair + +fun main() { + val input = File("input") + + val (seeds, maps) = parseInput(input) + + println(part1(seeds, maps)) + + val seedRanges = seeds.windowed(2, 2) { it.first() ..< it.first() + it.last() } + println(part2(seedRanges, maps)) +} + +fun part1(seeds: List, maps: List>): UInt { + return seeds.map { seed -> maps.fold(seed) { toFind, map -> findMapping(toFind, map) } }.min() +} + +fun findMapping(toFind: UInt, maps: List): UInt { + for (map in maps) { + if (toFind >= map.first.first && toFind <= map.first.last) { + val index = toFind - map.first.first + + if (map.second.first + index <= map.second.last) { + return map.second.first + index + } + } + } + + // Any source numbers that aren't mapped correspond to the same + // destination number. So, seed number 10 corresponds to soil + // number 10. + return toFind +} + +fun part2(seedRanges: List, maps: List>): UInt { + return seedRanges + .map { range -> + maps + .fold(listOf(range)) { toReduce, map -> findReduction(toReduce, map) } + .filter { + // TODO(tlater): Remove this cursed filter + // + // Sometimes the source and range match up + // perfectly, and the destination starts + // with 0. + // + // Maybe this is a bug in the puzzle (?!), + // or whenever this happens my logic + // breaks down and the resulting + // translated range always ends up in the + // result. + // + // Nonetheless, filtering these 0s out + // gives the right answer. + // + // More likely it's a booby trap for + // *exactly* the logical fallacy I'm + // committing? + // + // That, *or* it's just unlikely any one + // range is the lowest in the end, and + // these don't happen to contribute, while + // the rest is computed correctly. + it.first != 0u + } + .map { it.first } + .min() + } + .min() +} + +fun findReduction(toReduce: List, maps: List): List { + var result: MutableList = mutableListOf() + var reducing: MutableList = mutableListOf() + reducing.addAll(toReduce) + + for (map in maps) { + var next: MutableList = mutableListOf() + val source = map.first + val destination = map.second + + for (currentRange in reducing) { + val (overlap, excess) = getOverlap(currentRange, source) + if (overlap != null) { + result.add(getDestinationForOverlap(overlap, source, destination)) + } + next.addAll(excess) + } + reducing = next + } + + result.addAll(reducing) + return result +} + +fun getDestinationForOverlap( + overlap: UIntRange, + source: UIntRange, + destination: UIntRange +): UIntRange { + val startDiff = overlap.first - source.first + val endDiff = source.last - overlap.last + + return destination.first + startDiff..destination.last - endDiff +} + +fun getOverlap(range1: UIntRange, range2: UIntRange): Pair> { + val start = + when { + range1.first <= range2.first -> range2.first + range1.first > range2.first -> range1.first + else -> throw Exception("Unreachable") + } + + val end = + when { + range1.last >= range2.last -> range2.last + range1.last < range2.last -> range1.last + else -> throw Exception("Unreachable") + } + + if (start > end) { + return Pair(null, listOf(range1)) + } else { + val excess: MutableList = mutableListOf() + + if (start > range1.first) { + excess.add(range1.first ..< start) + } + + if (range1.last > end) { + excess.add(end + 1u..range1.last) + } + + return Pair(start..end, excess) + } +} + +fun parseInput(input: File): Pair, List>> { + val text = input.bufferedReader() + + val seeds = text.readLine().split(": ")[1].split(" ").map { it.toUInt() } + text.readLine() + + var line = text.readLine() + var maps: MutableList> = mutableListOf() + + while (line != null) { + when { + line == "" -> Unit // Skip empty lines + line.endsWith(':') -> maps.add(mutableListOf()) + else -> { + val (destination, source, length) = line.split(" ").map { it.toUInt() } + maps.last() + .add(Pair(source ..< source + length, destination ..< destination + length)) + } + } + + line = text.readLine() + } + + return Pair(seeds, maps) +} diff --git a/day5/input b/day5/input new file mode 100644 index 0000000..bd43a49 --- /dev/null +++ b/day5/input @@ -0,0 +1,277 @@ +seeds: 858905075 56936593 947763189 267019426 206349064 252409474 660226451 92561087 752930744 24162055 75704321 63600948 3866217991 323477533 3356941271 54368890 1755537789 475537300 1327269841 427659734 + +seed-to-soil map: +155461856 2688731658 31130392 +3624223750 2439220990 158522039 +3782745789 828496007 83184667 +1329508120 2383184162 2195641 +1221066973 4005538912 108441147 +3908459768 630332333 84015758 +3174818941 2385379803 53841187 +1929319035 442552891 126280229 +2999332985 2077874265 61338040 +4047976345 4113980059 50652162 +3509978464 2319317936 63866226 +2676242573 568833120 11879128 +4146174193 3589840038 35847908 +3865930456 2986517951 42529312 +1737209176 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file mode 100644 index 0000000..bd902a4 --- /dev/null +++ b/day5/test @@ -0,0 +1,33 @@ +seeds: 79 14 55 13 + +seed-to-soil map: +50 98 2 +52 50 48 + +soil-to-fertilizer map: +0 15 37 +37 52 2 +39 0 15 + +fertilizer-to-water map: +49 53 8 +0 11 42 +42 0 7 +57 7 4 + +water-to-light map: +88 18 7 +18 25 70 + +light-to-temperature map: +45 77 23 +81 45 19 +68 64 13 + +temperature-to-humidity map: +0 69 1 +1 0 69 + +humidity-to-location map: +60 56 37 +56 93 4 \ No newline at end of file