Upload solutions for day 18 of AOC 2023

src/aoc2023/Day18.kt

@@ -0,0 +1,85 @@
+package aoc2023
+
+import checkValue
+import readInput
+import kotlin.math.abs
+
+fun main() {
+    val (year, day) = "2023" to "Day18"
+
+    fun parsePlan(line: String, withHex: Boolean): Pair<Pair<Int, Int>, Long> {
+        val dir: Int
+        val distance: Long
+        if (withHex) {
+            val (_, _, hexStr) = line.split(" ")
+            val hex = hexStr.substring(2, hexStr.length - 1)
+            dir = hex.last().toString().toInt(radix = 16)
+            distance = hex.substring(0..4).toLong(radix = 16)
+        } else {
+            val (dirStr, distanceStr, _) = line.split(" ")
+            dir = "RDLU".indexOf(dirStr)
+            distance = distanceStr.toLong()
+        }
+        val dx = when (dir) {
+            0 -> 0 to 1
+            1 -> 1 to 0
+            2 -> 0 to -1
+            else -> -1 to 0
+        }
+        return dx to distance
+    }
+
+    fun polygonArea(holes: List<Hole>): Double {
+        var area = 0.0
+        var ref = holes.size - 1
+        for ((index, hole) in holes.withIndex()) {
+            area += (holes[ref].row + hole.row) * (holes[ref].col - hole.col)
+            ref = index
+        }
+        return abs(area / 2.0)
+    }
+
+    fun interiorPoints(holes: List<Hole>): Long {
+        val area = polygonArea(holes)
+        return (area - holes.size / 2.0 + 1).toLong()
+    }
+
+    fun cubicMeters(input: List<String>, withHex: Boolean): Long {
+        val borderHoles = mutableListOf<Hole>()
+        var currentHole = Hole(0, 0)
+        var minRow = Long.MAX_VALUE
+        var minCol = Long.MAX_VALUE
+        var maxRow = Long.MIN_VALUE
+        var maxCol = Long.MIN_VALUE
+        input.forEach { line ->
+            val (dx, distance) = parsePlan(line, withHex)
+            for (i in 1..distance) {
+                currentHole = currentHole.move(dx.first, dx.second)
+                borderHoles.add(currentHole)
+                minRow = minOf(minRow, currentHole.row)
+                maxRow = maxOf(maxRow, currentHole.row)
+                minCol = minOf(minCol, currentHole.col)
+                maxCol = maxOf(maxCol, currentHole.col)
+            }
+        }
+        val interiorPoints = interiorPoints(borderHoles)
+        return interiorPoints + borderHoles.size
+    }
+
+    fun part1(input: List<String>) = cubicMeters(input, withHex = false)
+
+    fun part2(input: List<String>) = cubicMeters(input, withHex = true)
+
+    val testInput = readInput(name = "${day}_test", year = year)
+    val input = readInput(name = day, year = year)
+
+    checkValue(part1(testInput), 62)
+    println(part1(input))
+
+    checkValue(part2(testInput), 952408144115)
+    println(part2(input))
+}
+
+data class Hole(val row: Long, val col: Long) {
+    fun move(dr: Int, dc: Int) = Hole(row + dr, col + dc)
+}