aoc2023/Day12.scala
2023-12-12 10:45:12 +01:00

56 lines
1.8 KiB
Scala

package aoc.day12
import aoc._
import scala.collection.mutable
case class Record(input: String, groups: List[Int]):
lazy val possibleFills = loop(0, groups)
def unfold(times: Int) =
Record((1 to times).map(_ => input).mkString("?"), (1 to times).flatMap(_ => groups).toList)
private inline def canEmpty(pos: Char) = pos == '.' || pos == '?'
private inline def canFill(pos: Char) = pos == '#' || pos == '?'
private val memo = mutable.Map.empty[(Int, Int), Long]
private def loop(from: Int, groups: List[Int]): Long =
if from == input.length() then (if groups.isEmpty then 1 else 0)
else
memo.getOrElseUpdate(
(from, groups.length), {
// don't fill this group
val noFill = if canEmpty(input(from)) then loop(from + 1, groups) else 0
// fill this group
val doFill = groups match
case head :: next if from + head <= input.length =>
val slice = input.slice(from, from + head)
if slice.forall(canFill(_)) then
if from + head == input.length() then loop(from + head, next)
else if canEmpty(input(from + head)) then loop(from + head + 1, next)
else 0
else 0
case _ => 0
noFill + doFill
}
)
object Parser extends CommonParser:
val groups = repsep(num, ",")
val record = """[?#.]+""".r ~ groups ^^ { case (input ~ groups) => Record(input, groups) }
def apply(s: String) = parse(record, s).get
val records = lines.map(Parser(_)).toSeq
def part1 =
val result = records.map(_.possibleFills).sum
println(result)
def part2 =
val result = records.map(_.unfold(5).possibleFills).sum
println(result)
@main def Day12(part: Int) = part match
case 1 => part1
case 2 => part2