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| 1 | +package net.olegg.aoc.year2024.day18 |
| 2 | + |
| 3 | +import net.olegg.aoc.someday.SomeDay |
| 4 | +import net.olegg.aoc.utils.Directions.Companion.NEXT_4 |
| 5 | +import net.olegg.aoc.utils.Vector2D |
| 6 | +import net.olegg.aoc.utils.parseInts |
| 7 | +import net.olegg.aoc.utils.get |
| 8 | +import net.olegg.aoc.utils.set |
| 9 | +import net.olegg.aoc.year2024.DayOf2024 |
| 10 | + |
| 11 | +/** |
| 12 | + * See [Year 2024, Day 18](https://adventofcode.com/2024/day/18) |
| 13 | + */ |
| 14 | +object Day18 : DayOf2024(18) { |
| 15 | + private val size = 71 |
| 16 | + |
| 17 | + override fun first(): Any? { |
| 18 | + val bytes = lines.map { line -> |
| 19 | + val (x, y) = line.parseInts(",") |
| 20 | + Vector2D(x, y) |
| 21 | + }.take(1024).toSet() |
| 22 | + |
| 23 | + val map = List(size) { y -> List(size) { x -> Vector2D(x, y) in bytes } } |
| 24 | + |
| 25 | + val start = Vector2D(0, 0) to 0 |
| 26 | + val finish = Vector2D(size - 1, size - 1) |
| 27 | + val queue = ArrayDeque(listOf(start)) |
| 28 | + val seen = mutableSetOf<Pair<Vector2D, Int>>() |
| 29 | + |
| 30 | + while (queue.isNotEmpty()) { |
| 31 | + val curr = queue.removeFirst() |
| 32 | + val (point, step) = curr |
| 33 | + if (point == finish) { |
| 34 | + return step |
| 35 | + } |
| 36 | + if (curr in seen) { |
| 37 | + continue |
| 38 | + } |
| 39 | + seen += curr |
| 40 | + |
| 41 | + queue += NEXT_4.map { point + it.step } |
| 42 | + .filter { map[it] == false } |
| 43 | + .map { it to step + 1 } |
| 44 | + } |
| 45 | + |
| 46 | + return -1 |
| 47 | + } |
| 48 | + |
| 49 | + override fun second(): Any? { |
| 50 | + val bytes = lines.map { line -> |
| 51 | + val (x, y) = line.parseInts(",") |
| 52 | + Vector2D(x, y) |
| 53 | + } |
| 54 | + |
| 55 | + var left = 0 |
| 56 | + var right = bytes.lastIndex |
| 57 | + var mid = (left + right) / 2 |
| 58 | + |
| 59 | + while (right - left > 1) { |
| 60 | + val cut = bytes.take(mid).toSet() |
| 61 | + val map = List(size) { y -> MutableList(size) { x -> Vector2D(x, y) in cut } } |
| 62 | + |
| 63 | + if (fill(map)) { |
| 64 | + left = mid |
| 65 | + } else { |
| 66 | + right = mid |
| 67 | + } |
| 68 | + mid = (left + right) / 2 |
| 69 | + } |
| 70 | + |
| 71 | + return bytes[left].let { "${it.x},${it.y}" } |
| 72 | + } |
| 73 | + |
| 74 | + private fun fill(map: List<MutableList<Boolean>>): Boolean { |
| 75 | + val start = Vector2D(0, 0) |
| 76 | + val finish = Vector2D(size - 1, size - 1) |
| 77 | + val queue = ArrayDeque(listOf(start)) |
| 78 | + val seen = mutableSetOf<Vector2D>() |
| 79 | + |
| 80 | + while (queue.isNotEmpty()) { |
| 81 | + val curr = queue.removeFirst() |
| 82 | + if (curr == finish) { |
| 83 | + return true |
| 84 | + } |
| 85 | + if (curr in seen) { |
| 86 | + continue |
| 87 | + } |
| 88 | + seen += curr |
| 89 | + |
| 90 | + val next = NEXT_4.map { curr + it.step } |
| 91 | + .filter { map[it] == false } |
| 92 | + |
| 93 | + next.forEach { map[it] = true } |
| 94 | + |
| 95 | + queue += next |
| 96 | + } |
| 97 | + |
| 98 | + return map[finish]!! |
| 99 | + } |
| 100 | +} |
| 101 | + |
| 102 | +fun main() = SomeDay.mainify(Day18) |
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