Day 15: Lens Library

Megathread guidelines

  • Keep top level comments as only solutions, if you want to say something other than a solution put it in a new post. (replies to comments can be whatever)
  • Code block support is not fully rolled out yet but likely will be in the middle of the event. Try to share solutions as both code blocks and using something such as https://topaz.github.io/paste/ , pastebin, or github (code blocks to future proof it for when 0.19 comes out and since code blocks currently function in some apps and some instances as well if they are running a 0.19 beta)

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  • @cvttsd2si
    4•7 months ago

    Scala3

    def hash(s: String): Long = s.foldLeft(0)((h, c) => (h + c)*17 % 256)

extension [A] (a: List[A])
    def mapAtIndex(idx: Long, f: A => A): List[A] =
        a.zipWithIndex.map((e, i) => if i == idx then f(e) else e)

def runProcedure(steps: List[String]): Long =
    @tailrec def go(boxes: List[List[(String, Int)]], steps: List[String]): List[List[(String, Int)]] =
        steps match
            case s"$label-" :: t =>
                go(boxes.mapAtIndex(hash(label), _.filter(_._1 != label)), t)
            case s"$label=$f" :: t =>
                go(boxes.mapAtIndex(hash(label), b => 
                    val slot = b.map(_._1).indexOf(label)
                    if slot != -1 then b.mapAtIndex(slot, (l, _) => (l, f.toInt)) else (label, f.toInt) :: b
                ), t)
            case _ => boxes
    
    go(List.fill(256)(List()), steps).zipWithIndex.map((b, i) =>
        b.zipWithIndex.map((lens, ilens) => (1 + i) * (b.size - ilens) * lens._2).sum
    ).sum

def task1(a: List[String]): Long = a.head.split(",").map(hash).sum
def task2(a: List[String]): Long = runProcedure(a.head.split(",").toList)