day 14

src/main/kotlin/me/gergo/Aoc14.kt

@@ -0,0 +1,96 @@
+package me.gergo
+
+import java.io.File
+import kotlin.math.max
+import kotlin.math.min
+
+fun main() {
+    val rockPaths = File("src/main/resources/input14.txt").readLines()
+        .map {
+            it.split(" -> ").map { c ->
+                val (x, y) = c.split(",")
+                Coordinate(x.toInt(), y.toInt())
+            }
+        }
+    val cave = Cave(rockPaths, 2000) // Set floorWidth=0 for Part One... yeah, it's not very elegant, but it worked :)
+
+    while (cave.pourSandAt(Coordinate(500, 0))) {
+    }
+
+    println(cave)
+    println("Sand at rest: ${cave.sandCount()}")
+}
+
+private class Cave(rockPaths: List<List<Coordinate>>, val floorWidth: Int) {
+    private val minX: Int
+    private val minY: Int
+    private val width: Int
+    private val height: Int
+    private val cells: Array<CharArray>
+
+    init {
+        val allCoordinates = rockPaths.flatten()
+        minX = min(-floorWidth, allCoordinates.minOf { it.x })
+        minY = min(0, allCoordinates.minOf { it.y })
+        width = max(allCoordinates.maxOf { it.x } - minX, floorWidth * 2) + 1
+        height = allCoordinates.maxOf { it.y } - minY + 1 + 2
+        cells = Array(height) { CharArray(width) { '.' } }
+
+        for (rockPath in rockPaths) {
+            rockPath.windowed(2) { (a, b) ->
+                if (a.x == b.x) {
+                    for (y in min(a.y, b.y)..max(a.y, b.y)) this[a.x, y] = '#'
+                } else if (a.y == b.y) {
+                    for (x in min(a.x, b.x)..max(a.x, b.x)) this[x, a.y] = '#'
+                }
+            }
+        }
+
+        if (floorWidth > 0) {
+            for (x in -floorWidth..floorWidth) this[x, height - minY - 1] = '#'
+        }
+    }
+
+    operator fun get(x: Int, y: Int): Char {
+        return cells[y - minY][x - minX]
+    }
+
+    operator fun set(x: Int, y: Int, value: Char) {
+        cells[y - minY][x - minX] = value
+    }
+
+    override fun toString(): String {
+        val buf = StringBuilder(height * (width + 1))
+        for (y in 0 until height) {
+            for (x in 0 until width) {
+                buf.append(cells[y][x])
+            }
+            buf.append('\n')
+        }
+        return buf.toString()
+    }
+
+    fun pourSandAt(start: Coordinate): Boolean {
+        if (!isFree(start.x, start.y)) return false // We're full at the starting coordinate
+
+        var x = start.x
+        for (y in 0..minY + height) {
+            if (isOutside(x, y)) break
+            if (isFree(x, y + 1)) continue
+            else if (isFree(x - 1, y + 1)) {
+                x--
+            } else if (isFree(x + 1, y + 1)) {
+                x++
+            } else {
+                this[x, y] = 'o'
+                return true // Settled
+            }
+        }
+        return false
+    }
+
+    fun sandCount() = cells.sumOf { lines -> lines.count { it == 'o' } }
+
+    private fun isFree(x: Int, y: Int) = isOutside(x, y) || (this[x, y] != '#' && this[x, y] != 'o')
+    private fun isOutside(x: Int, y: Int) = x < minX || x >= width + minX || y < minY || y >= height + minY
+}