Move subproject to avoid IntelliJ module name issues

1 files changed, 87 insertions, 0 deletions

diff --git a/aoc-2021-kotlin/src/Day25.kt b/aoc-2021-kotlin/src/Day25.kt
new file mode 100644
index 0000000..36a2f75
--- /dev/null
+++ b/aoc-2021-kotlin/src/Day25.kt
@@ -0,0 +1,87 @@
+object Day25 {
+    private class SeaCucumbers(private val width: Int, private val height: Int, private val matrix: Array<SeaTile>) {
+        companion object {
+            fun fromLines(lines: List<String>) =
+                Pos2D(
+                    lines.getOrNull(0)?.length ?: throw IllegalArgumentException("Sea must have a non-zero height!"),
+                    lines.size
+                ).let { size ->
+                    SeaCucumbers(size.x, size.y, Array(size.x * size.y) {
+                        when (val char = lines[it / size.x][it % size.x]) {
+                            '>' -> SeaTile.Cucumber.EastFacing
+                            'v' -> SeaTile.Cucumber.SouthFacing
+                            '.' -> SeaTile.EmptyTile
+                            else -> throw IllegalArgumentException("Found '$char', expected '>', 'v' or '.'!")
+                        }
+                    })
+                }
+        }
+
+        private sealed class SeaTile {
+            object EmptyTile : SeaTile()
+            sealed class Cucumber : SeaTile() {
+                object EastFacing : Cucumber()
+                object SouthFacing : Cucumber()
+            }
+        }
+
+        private fun moveIndex(index: Int, offset: Pos2D) =
+            ((index / width + offset.y) % height) * width + (index + offset.x) % width
+
+        private inline fun <reified T : SeaTile.Cucumber> stepDirection(pos: Pos2D) {
+            matrix
+                .asSequence()
+                .withIndex()
+                .map { (index, seaTile) ->
+                    val nextIndex = moveIndex(index, pos)
+                    if (seaTile is T && matrix[nextIndex] is SeaTile.EmptyTile) {
+                        index to nextIndex
+                    } else {
+                        null
+                    }
+                }
+                .filterNotNull()
+                .toList()
+                .forEach { (index, nextIndex) ->
+                    matrix[nextIndex] = matrix[index].also { matrix[index] = SeaTile.EmptyTile }
+                }
+        }
+
+        private fun stepOnce() {
+            stepDirection<SeaTile.Cucumber.EastFacing>(Pos2D(1, 0))
+            stepDirection<SeaTile.Cucumber.SouthFacing>(Pos2D(0, 1))
+        }
+
+        fun simulate(): Int {
+            var count = 0
+
+            do {
+                val previousHashCode = matrix.contentHashCode()
+                stepOnce()
+                count++
+            } while (matrix.contentHashCode() != previousHashCode)
+
+            return count
+        }
+
+        override fun toString(): String = matrix
+            .withIndex()
+            .joinToString("") { (index, seaTile) ->
+                when (seaTile) {
+                    SeaTile.Cucumber.EastFacing -> ">"
+                    SeaTile.Cucumber.SouthFacing -> "v"
+                    SeaTile.EmptyTile -> "."
+                } + (if (index % width == width - 1) "\n" else "")
+            }
+    }
+
+    fun singlePart(input: List<String>) = SeaCucumbers.fromLines(input).simulate()
+}
+
+fun main() {
+    val testInput = readInputAsLines("Day25_test")
+    check(Day25.singlePart(testInput) == 58)
+
+    val input = readInputAsLines("Day25")
+    println(Day25.singlePart(input))
+}