Day 19 part 1

2024/src/main/kotlin/day19.kt

@@ -0,0 +1,21 @@
+fun main() {
+    val iterator = readInput("day19.txt").iterator()
+
+    val towels = Sequence { iterator }.takeWhile { it.isNotEmpty() }
+        .flatMap { it.split(",\\s*".toRegex()) }
+        .toList()
+
+    val part1 = Sequence { iterator }.count { isPossible(it, towels) }
+    println("Part 1: $part1")
+}
+
+private val patternMemo = mutableMapOf<String, Boolean>()
+
+fun isPossible(pattern: String, towels: List<String>): Boolean {
+    if (pattern.isEmpty()) return true
+    return patternMemo.getOrPut(pattern) {
+        towels
+            .filter { pattern.startsWith(it) }
+            .any { isPossible(pattern.substring(it.length), towels) }
+    }
+}