Solution for 2023-12-12, part 1 (bruteforce)

src/main/kotlin/biz/koziolek/adventofcode/year2023/day12/day12.kt

@@ -0,0 +1,54 @@
+package biz.koziolek.adventofcode.year2023.day12
+
+import biz.koziolek.adventofcode.findInput
+
+fun main() {
+    val inputFile = findInput(object {})
+    val springs = parseHotSpringsRecords(inputFile.bufferedReader().readLines())
+    println("There are ${countPossibleArrangements(springs)} possible arrangements")
+}
+
+const val OPERATIONAL = '.'
+const val DAMAGED = '#'
+const val UNKNOWN = '?'
+
+data class HotSpringsRow(val conditions: String, val damagedGroupSizes: List<Int>) {
+    val isUnknown = UNKNOWN in conditions
+}
+
+fun parseHotSpringsRecords(lines: Iterable<String>): List<HotSpringsRow> =
+    lines
+        .map { line ->
+            val (conditions, sizesStr) = line.split(" ")
+            val sizes = sizesStr.split(",").map { it.toInt() }
+            HotSpringsRow(conditions, sizes)
+        }
+
+fun springsMatch(conditions: String, damagedGroupSizes: List<Int>): Boolean =
+    conditions
+        .trim(OPERATIONAL)
+        .replace(Regex(Regex.escape(OPERATIONAL.toString()) + "+"), OPERATIONAL.toString())
+        .split(OPERATIONAL)
+        .map { it.length }
+        .let { it == damagedGroupSizes }
+
+fun generatePossibleArrangements(hotSpringsRow: HotSpringsRow): Sequence<HotSpringsRow> =
+    sequence {
+        if (!hotSpringsRow.isUnknown) {
+            if (springsMatch(hotSpringsRow.conditions, hotSpringsRow.damagedGroupSizes)) {
+                yield(hotSpringsRow)
+            }
+        } else {
+            val (first, second) = hotSpringsRow.conditions.split(UNKNOWN, limit = 2)
+
+            yieldAll(generatePossibleArrangements(
+                HotSpringsRow(first + OPERATIONAL + second, hotSpringsRow.damagedGroupSizes)
+            ))
+            yieldAll(generatePossibleArrangements(
+                HotSpringsRow(first + DAMAGED + second, hotSpringsRow.damagedGroupSizes)
+            ))
+        }
+    }
+
+fun countPossibleArrangements(hotSpringsRows: List<HotSpringsRow>): Int =
+    hotSpringsRows.sumOf { generatePossibleArrangements(it).count() }