Day 24: Blizzard Basin

README.md

@@ -29,4 +29,4 @@ Development occurs in language-specific directories:
 |[Day21.hs](hs/src/Day21.hs)|[Day21.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day21.kt)|[day21.py](py/aoc2022/day21.py)|[day21.rs](rs/src/day21.rs)|
 |[Day22.hs](hs/src/Day22.hs)|[Day22.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day22.kt)|[day22.py](py/aoc2022/day22.py)|[day22.rs](rs/src/day22.rs)|
 |[Day23.hs](hs/src/Day23.hs)|[Day23.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day23.kt)|[day23.py](py/aoc2022/day23.py)|[day23.rs](rs/src/day23.rs)|
-|[Day24.hs](hs/src/Day24.hs)|
+|[Day24.hs](hs/src/Day24.hs)|[Day24.kt](kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day24.kt)|

kt/src/commonMain/kotlin/com/github/ephemient/aoc2022/Day24.kt

@@ -0,0 +1,56 @@
+package com.github.ephemient.aoc2022
+
+import kotlin.math.abs
+
+@Day
+class Day24(private val lines: List<String>) {
+    private val start = lines.first().indexOf('.') to 0
+    private val end = lines.last().lastIndexOf('.') to lines.lastIndex
+
+    @Suppress("ComplexCondition")
+    private fun isFree(x: Int, y: Int, time: Int): Boolean {
+        if (x <= 0 || y <= 0 || y >= lines.lastIndex || x >= lines.getOrElse(y) { "" }.lastIndex) {
+            return (lines.getOrNull(y)?.getOrNull(x) ?: '#') == '.'
+        }
+        return lines[y][(x - 1 + time).mod(lines[y].length - 2) + 1] != '<' &&
+            lines[y][(x - 1 - time).mod(lines[y].length - 2) + 1] != '>' &&
+            lines[(y - 1 + time).mod(lines.size - 2) + 1][x] != '^' &&
+            lines[(y - 1 - time).mod(lines.size - 2) + 1][x] != 'v'
+    }
+
+    private fun search(start: IntPair, end: IntPair, startTime: Int = 0): Int {
+        val (endX, endY) = end
+        val queue = PriorityQueue(compareBy(IndexedValue<IndexedValue<IntPair>>::index))
+        queue.add(IndexedValue(0, IndexedValue(startTime, start)))
+        val seen = mutableSetOf<IndexedValue<IntPair>>()
+        while (!queue.isEmpty()) {
+            val entry = queue.remove().value
+            if (!seen.add(entry)) continue
+            val (time, position) = entry
+            if (position == end) return time
+            val (x, y) = position
+            if (isFree(x, y, time + 1)) {
+                queue.add(IndexedValue(time + abs(x - endX) + abs(y - endY), IndexedValue(time + 1, x to y)))
+            }
+            if (isFree(x - 1, y, time + 1)) {
+                queue.add(IndexedValue(time + abs(x - 1 - endX) + abs(y - endY), IndexedValue(time + 1, x - 1 to y)))
+            }
+            if (isFree(x + 1, y, time + 1)) {
+                queue.add(IndexedValue(time + abs(x + 1 - endX) + abs(y - endY), IndexedValue(time + 1, x + 1 to y)))
+            }
+            if (isFree(x, y - 1, time + 1)) {
+                queue.add(IndexedValue(time + abs(x - endX) + abs(y - 1 - endY), IndexedValue(time + 1, x to y - 1)))
+            }
+            if (isFree(x, y + 1, time + 1)) {
+                queue.add(IndexedValue(time + abs(x - endX) + abs(y + 1 - endY), IndexedValue(time + 1, x to y + 1)))
+            }
+        }
+        throw NoSuchElementException()
+    }
+
+    @Day.Part
+    fun part1(): Int = search(start, end)
+
+    @Day.Part
+    fun part2(): Int = search(start, end, search(end, start, search(start, end)))
+}

kt/src/commonTest/kotlin/com/github/ephemient/aoc2022/Day24Test.kt

@@ -0,0 +1,16 @@
+package com.github.ephemient.aoc2022
+
+import kotlin.test.Test
+import kotlin.test.assertEquals
+
+class Day24Test {
+    @Test
+    fun part1() {
+        assertEquals(18, Day24(getTestInput(24)).part1())
+    }
+
+    @Test
+    fun part2() {
+        assertEquals(54, Day24(getTestInput(24)).part2())
+    }
+}

kt/src/jvmTest/resources/day24.txt

@@ -0,0 +1,6 @@
+#.######
+#>>.<^<#
+#.<..<<#
+#>v.><>#
+#<^v^^>#
+######.#