Day 16

src/main/kotlin/y2024/day16/Day16.kt

@@ -0,0 +1,159 @@
+package y2024.day16
+
+import utils.Point
+import utils.getInputFile
+import utils.toPointGrid
+import java.util.*
+
+fun main() {
+    println("Part one: " + Day16.solvePartOne())
+    println("Part two: " + Day16.solvePartTwo())
+}
+
+object Day16 {
+
+    private val input = getInputFile(this::class.java.packageName, example = false)
+        .readLines()
+        .toPointGrid()
+
+    fun solvePartOne(): Int {
+        val start = input.entries.find { it.value == 'S' }!!.key
+        val end = input.entries.find { it.value == 'E' }!!.key
+        val movementQueue: PriorityQueue<Triple<Point, Direction, Int>> = PriorityQueue(compareBy { it.third })
+        movementQueue += Triple(start, Direction.EAST, 0)
+
+        val visited = mutableSetOf(start to Direction.EAST)
+        val scores = mutableListOf<Int>()
+
+        while (movementQueue.isNotEmpty()) {
+            val (point, direction, score) = movementQueue.poll()
+            visited += point to direction
+
+            val n = point.n
+            if (n == end) {
+                scores += score + 1 + direction.rotationScore(Direction.NORTH)
+            } else if ((n to Direction.NORTH) !in visited && !input.isWall(n)) {
+                movementQueue += Triple(n, Direction.NORTH, score + 1 + direction.rotationScore(Direction.NORTH))
+            }
+
+            val e = point.e
+            if (e == end) {
+                scores += score + 1 + direction.rotationScore(Direction.EAST)
+            } else if ((e to Direction.EAST) !in visited && !input.isWall(e)) {
+                movementQueue += Triple(e, Direction.EAST, score + 1 + direction.rotationScore(Direction.EAST))
+            }
+
+            val s = point.s
+            if (s == end) {
+                scores += score + 1 + direction.rotationScore(Direction.SOUTH)
+            } else if ((s to Direction.SOUTH) !in visited && !input.isWall(s)) {
+                movementQueue += Triple(s, Direction.SOUTH, score + 1 + direction.rotationScore(Direction.SOUTH))
+            }
+
+            val w = point.w
+            if (w == end) {
+                scores += score + 1 + direction.rotationScore(Direction.WEST)
+            } else if ((w to Direction.WEST) !in visited && !input.isWall(w)) {
+                movementQueue += Triple(w, Direction.WEST, score + 1 + direction.rotationScore(Direction.WEST))
+            }
+        }
+
+        return scores.min()
+    }
+
+    data class Path(
+        val currentPoint: Point,
+        val currentDirection: Direction,
+        val score: Int,
+        val visited: Set<Point>,
+    )
+
+    data class GoodPath(
+        val score: Int,
+        val path: Set<Point>,
+    )
+
+    fun solvePartTwo(): Int {
+        val start = input.entries.find { it.value == 'S' }!!.key
+        val end = input.entries.find { it.value == 'E' }!!.key
+        val movementQueue: PriorityQueue<Path> = PriorityQueue(compareBy { it.score })
+        movementQueue += Path(start, Direction.EAST, 0, setOf(start, end))
+
+        val visited = mutableSetOf(start to Direction.EAST)
+        val scores = mutableListOf<GoodPath>()
+
+        while (movementQueue.isNotEmpty()) {
+            val (point, direction, score, path) = movementQueue.poll()
+            visited += point to direction
+
+            val n = point.n
+            if (n == end) {
+                scores += GoodPath(score + 1 + direction.rotationScore(Direction.NORTH), path + n)
+            } else if ((n to Direction.NORTH) !in visited && !input.isWall(n)) {
+                movementQueue += Path(n, Direction.NORTH, score + 1 + direction.rotationScore(Direction.NORTH), path + n)
+            }
+
+            val e = point.e
+            if (e == end) {
+                scores += GoodPath(score + 1 + direction.rotationScore(Direction.EAST), path + e)
+            } else if ((e to Direction.EAST) !in visited && !input.isWall(e)) {
+                movementQueue += Path(e, Direction.EAST, score + 1 + direction.rotationScore(Direction.EAST), path + e)
+            }
+
+            val s = point.s
+            if (s == end) {
+                scores += GoodPath(score + 1 + direction.rotationScore(Direction.SOUTH), path + s)
+            } else if ((s to Direction.SOUTH) !in visited && !input.isWall(s)) {
+                movementQueue += Path(s, Direction.SOUTH, score + 1 + direction.rotationScore(Direction.SOUTH), path + s)
+            }
+
+            val w = point.w
+            if (w == end) {
+                scores += GoodPath(score + 1 + direction.rotationScore(Direction.WEST), path + w)
+            } else if ((w to Direction.WEST) !in visited && !input.isWall(w)) {
+                movementQueue += Path(w, Direction.WEST, score + 1 + direction.rotationScore(Direction.WEST), path + w)
+            }
+        }
+
+        val lowestScore = scores.minOfOrNull { it.score } ?: Integer.MAX_VALUE
+
+        return scores
+            .filter { it.score == lowestScore }
+            .flatMap { it.path }
+            .toSet()
+            .size
+    }
+
+    enum class Direction {
+        NORTH, EAST, SOUTH, WEST;
+
+        fun rotationScore(other: Direction): Int = when (this) {
+            NORTH -> when (other) {
+                NORTH -> 0
+                EAST -> 1000
+                SOUTH -> 2000
+                WEST -> 1000
+            }
+            EAST -> when (other) {
+                NORTH -> 1000
+                EAST -> 0
+                SOUTH -> 1000
+                WEST -> 2000
+            }
+            SOUTH -> when (other) {
+                NORTH -> 2000
+                EAST -> 1000
+                SOUTH -> 0
+                WEST -> 1000
+            }
+            WEST -> when (other) {
+                NORTH -> 1000
+                EAST -> 2000
+                SOUTH -> 1000
+                WEST -> 0
+            }
+        }
+    }
+
+    private fun Map<Point, Char>.isWall(point: Point) = get(point) == '#'
+}

src/main/kotlin/y2024/day16/example.txt

@@ -0,0 +1,15 @@
+###############
+#.......#....E#
+#.#.###.#.###.#
+#.....#.#...#.#
+#.###.#####.#.#
+#.#.#.......#.#
+#.#.#####.###.#
+#...........#.#
+###.#.#####.#.#
+#...#.....#.#.#
+#.#.#.###.#.#.#
+#.....#...#.#.#
+#.###.#.#.#.#.#
+#S..#.....#...#
+###############

src/test/kotlin/y2024/day16/Day16Test.kt

@@ -0,0 +1,16 @@
+package y2024.day16
+
+import org.junit.jupiter.api.Assertions.assertEquals
+import org.junit.jupiter.api.Test
+
+internal class Day16Test {
+    @Test
+    fun solvePartOne() {
+        assertEquals(108504, Day16.solvePartOne())
+    }
+
+    @Test
+    fun solvePartTwo() {
+        assertEquals(538, Day16.solvePartTwo())
+    }
+}