Add Day15

src/main/kotlin/Day15.kt

@@ -0,0 +1,79 @@
+import utils.AoCDay
+import utils.Vec2D
+import utils.chunkedInput
+import utils.toPointMap
+
+class Day15 : AoCDay() {
+
+    val chunks = input.chunkedInput()
+    val grid = chunks.first().toPointMap().toMutableMap()
+    val instructions = chunks.last().joinToString("").map {
+        when (it) {
+            '^' -> Vec2D.UP
+            'v' -> Vec2D.DOWN
+            '>' -> Vec2D.RIGHT
+            '<' -> Vec2D.LEFT
+            else -> error("Invalid instruction $it")
+        }
+    }
+
+    override fun part1(): Any {
+        val boxes = grid.keys.filter { grid[it] == 'O' || grid[it] == '@' }.toSet()
+        val walls = grid.keys.filter { grid[it] == '#' }.toSet()
+        var start = grid.filter { it.value == '@' }.entries.first().key
+
+        val (finalRobot, finalBoxes) = instructions.fold(start to boxes) { (robot, boxes), dir ->
+            val toMove = generateSequence(robot) { it + dir }
+                .takeWhile { it in boxes }
+                .toList()
+            if (toMove.last() + dir in walls) {
+                robot to boxes
+            } else {
+                val boxesToStay = boxes - toMove.toSet()
+
+                (robot + dir) to (boxesToStay + toMove.map { it + dir }.toSet())
+            }
+        }
+
+        return (finalBoxes - finalRobot).sumOf { it.y * 100 + it.x }
+    }
+
+    override fun part2(): Any {
+        val boxes = grid.keys.filter { grid[it] == 'O' }.map {
+            Vec2D(it.x * 2, it.y) to Vec2D(it.x * 2 + 1, it.y)
+        }.toSet()
+
+        val walls = grid.keys.filter { grid[it] == '#' }.map {
+            listOf(Vec2D(it.x * 2, it.y), Vec2D(it.x * 2 + 1, it.y))
+        }.flatten().toSet()
+
+        var start = grid.filter { it.value == '@' }.entries.first().key.let { Vec2D(it.x * 2, it.y) }
+
+        val (_, finalBoxes) = instructions.fold(start to boxes) { (robot, boxes), dir ->
+            val movingBlocks = generateSequence(setOf(robot)) { current ->
+                val next = current.map { it + dir }
+                val front = boxes.filter { it.first in next || it.second in next }
+
+                current + front.flatMap { it.toList() }
+            }
+                .zipWithNext()
+                .first { it.first == it.second }
+                .first
+
+            if (movingBlocks.any { it + dir in walls }) {
+                robot to boxes
+            } else {
+                val (boxesToMove, boxesToStay) = boxes.partition { it.first in movingBlocks }
+
+                (robot + dir) to (boxesToStay + boxesToMove.map { it.first + dir to it.second + dir }).toSet()
+
+            }
+        }
+
+        return finalBoxes.sumOf { it.first.y * 100 + it.first.x }
+    }
+}
+
+fun main() {
+    Day15().execute()
+}