Add day 19 code.

Author: AvaPL

2024/src/day19.scala

@@ -0,0 +1,56 @@
+package day19
+
+import scala.collection.mutable
+
+import locations.Directory.currentDir
+import inputs.Input.loadFileSync
+
+@main def part1: Unit =
+  println(s"The solution is ${part1(loadInput())}")
+
+@main def part2: Unit =
+  println(s"The solution is ${part2(loadInput())}")
+
+def loadInput(): String = loadFileSync(s"$currentDir/../input/day19")
+
+type Towel = String
+type Pattern = String
+
+def parse(input: String): (List[Towel], List[Pattern]) =
+  val Array(towelsString, patternsString) = input.split("\n\n")
+  val towels = towelsString.split(", ").toList
+  val patterns = patternsString.split("\n").toList
+  (towels, patterns)
+
+def part1(input: String): Int =
+  val (towels, patterns) = parse(input)
+  val possiblePatterns = patterns.filter(isPossible(towels))
+  possiblePatterns.size
+
+def isPossible(towels: List[Towel])(pattern: Pattern): Boolean =
+  val regex = towels.mkString("^(", "|", ")*$").r
+  regex.matches(pattern)
+
+def part2(input: String): Long =
+  val (towels, patterns) = parse(input)
+  countOptions(towels, patterns)
+
+def countOptions(towels: List[Towel], patterns: List[Pattern]): Long =
+  val cache = mutable.Map.empty[Pattern, Long]
+
+  def loop(pattern: Pattern): Long =
+    cache.getOrElseUpdate(
+      pattern,
+      towels
+        .collect {
+          case towel if pattern.startsWith(towel) =>
+            pattern.drop(towel.length)
+        }
+        .map { remainingPattern =>
+          if (remainingPattern.isEmpty) 1
+          else loop(remainingPattern)
+        }
+        .sum
+    )
+
+  patterns.map(loop).sum