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| 1 | +package net.olegg.aoc.year2024.day21 |
| 2 | + |
| 3 | +import net.olegg.aoc.someday.SomeDay |
| 4 | +import net.olegg.aoc.utils.Directions |
| 5 | +import net.olegg.aoc.utils.Vector2D |
| 6 | +import net.olegg.aoc.utils.find |
| 7 | +import net.olegg.aoc.utils.get |
| 8 | +import net.olegg.aoc.utils.permutations |
| 9 | +import net.olegg.aoc.year2024.DayOf2024 |
| 10 | + |
| 11 | +/** |
| 12 | + * See [Year 2024, Day 21](https://adventofcode.com/2024/day/21) |
| 13 | + */ |
| 14 | +object Day21 : DayOf2024(21) { |
| 15 | + private val pattern = "(\\d+)".toRegex() |
| 16 | + private val digits = """ |
| 17 | + 789 |
| 18 | + 456 |
| 19 | + 123 |
| 20 | + 0A |
| 21 | + """.trimIndent().lines().map { it.toList() } |
| 22 | + private val arms = """ |
| 23 | + ^A |
| 24 | + <v> |
| 25 | + """.trimIndent().lines().map { it.toList() } |
| 26 | + |
| 27 | + override fun first(): Any? { |
| 28 | + val digitsMap = digits.flatMapIndexed { y, row -> |
| 29 | + row.mapIndexedNotNull { x, c -> |
| 30 | + if (c != ' ') c to Vector2D(x, y) else null |
| 31 | + } |
| 32 | + }.toMap() |
| 33 | + |
| 34 | + return lines.sumOf { line -> |
| 35 | + val code = pattern.find(line)?.value?.toIntOrNull() ?: 0 |
| 36 | + |
| 37 | + val length = "A$line" |
| 38 | + .zipWithNext { a, b -> bestPath(digits, arms, digitsMap[a]!!, digitsMap[b]!!, 0) } |
| 39 | + .sum() |
| 40 | + |
| 41 | + code * length |
| 42 | + } |
| 43 | + } |
| 44 | + |
| 45 | + private val bestCache = mutableMapOf<Triple<Vector2D, Vector2D, Int>, Int>() |
| 46 | + |
| 47 | + private fun bestPath( |
| 48 | + matrix: List<List<Char>>, |
| 49 | + handler: List<List<Char>>, |
| 50 | + from: Vector2D, |
| 51 | + to: Vector2D, |
| 52 | + level: Int, |
| 53 | + ): Int { |
| 54 | + val config = Triple(from, to, level) |
| 55 | + return when { |
| 56 | + level == 3 -> 1 |
| 57 | + config in bestCache -> bestCache[config]!! |
| 58 | + from == to -> 1 |
| 59 | + else -> { |
| 60 | + val delta = to - from |
| 61 | + val basePath = buildList { |
| 62 | + when { |
| 63 | + delta.x > 0 -> repeat(delta.x) { add(Directions.R) } |
| 64 | + delta.x < 0 -> repeat(-delta.x) { add(Directions.L) } |
| 65 | + } |
| 66 | + when { |
| 67 | + delta.y > 0 -> repeat(delta.y) { add(Directions.D) } |
| 68 | + delta.y < 0 -> repeat(-delta.y) { add(Directions.U) } |
| 69 | + } |
| 70 | + } |
| 71 | + |
| 72 | + val best = basePath.permutations() |
| 73 | + .filter { path -> |
| 74 | + path.scan(from) { curr, dir -> curr + dir.step }.none { matrix[it] == ' ' } |
| 75 | + } |
| 76 | + .minOf { path -> |
| 77 | + val chars = buildList { |
| 78 | + add('A') |
| 79 | + path.forEach { |
| 80 | + when (it) { |
| 81 | + Directions.L -> add('<') |
| 82 | + Directions.R -> add('>') |
| 83 | + Directions.U -> add('^') |
| 84 | + Directions.D -> add('v') |
| 85 | + else -> Unit |
| 86 | + } |
| 87 | + } |
| 88 | + add('A') |
| 89 | + } |
| 90 | + |
| 91 | + chars.zipWithNext().sumOf { (fromChar, toChar) -> |
| 92 | + val fromPoint = handler.find(fromChar)!! |
| 93 | + val toPoint = handler.find(toChar)!! |
| 94 | + bestPath(handler, handler, fromPoint, toPoint, level + 1) |
| 95 | + } |
| 96 | + } |
| 97 | + |
| 98 | + bestCache[config] = best |
| 99 | + best |
| 100 | + } |
| 101 | + } |
| 102 | + } |
| 103 | +} |
| 104 | + |
| 105 | +fun main() = SomeDay.mainify(Day21) |
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