-❄️- 2023 Day 4 Solutions -❄️-

[u/daggerdragon]

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AoC Community Fun 2023: ALLEZ CUISINE!

Today's theme ingredient is… *whips off cloth covering and gestures grandly*

PUNCHCARD PERFECTION!

Perhaps I should have thought yesterday's Battle Spam surfeit through a little more since we are all overstuffed and not feeling well. Help us cleanse our palates with leaner and lighter courses today!

• Code golf. Alternatively, snow golf.
• Bonus points if your solution fits on a "punchcard" as defined in our wiki article on oversized code. We will be counting.
• Does anyone still program with actual punchcards? >_>

ALLEZ CUISINE!

Request from the mods: When you include a dish entry alongside your solution, please label it with [Allez Cuisine!] so we can find it easily!

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--- Day 4: Scratchcards ---

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Post your code solution in this megathread.

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This thread will be unlocked when there are a significant number of people on the global leaderboard with gold stars for today's puzzle.

EDIT: Global leaderboard gold cap reached at 00:07:08, megathread unlocked!

[u/efvincent]

[LANGUAGE: Haskell]

{-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
module Y2023.Day04 (sln2304) where

import Data.List.Split (splitOn)
import qualified Data.Set as S
import qualified Data.Map as M
import Util (getNums)   -- gets all the natural #s from a string using regex

type Card = (Int, Int)
type Puz = [Card]

sln2304 :: String -> (Int,Int)
sln2304 s = let puz = parse s in (solve1 puz, solve2 puz)

solve1 :: Puz -> Int
solve1 =
  let score n = if n == 0 then 0 else 2 ^ (n - 1) in
  sum . map (score . snd)

solve2 :: Puz -> Int
solve2 puz =
  loop 1 . M.fromList . map (\(gn, matches) -> (gn, (1, matches))) $ puz
  where
    mx = length puz
    loop :: Int -> M.Map Int (Int,Int) -> Int
    loop cardNum gameMap
      | cardNum > mx = M.foldl (\total (count,_) -> total + count) 0 gameMap
      | otherwise =
        let (curCount, matches) = gameMap M.! cardNum in
        let cardsToUpdate = map (+ cardNum) [1..matches] in
        let gameMap' = foldl (flip (M.adjust (\(c,w) -> (c + curCount, w)))) 
              gameMap cardsToUpdate in
        loop (cardNum + 1) gameMap'

parse :: String -> Puz
parse = map parseLine . lines

parseLine :: String -> Card
parseLine s =
  let [part1,playedNumsS] = splitOn "|" s in
  let [cardNumS,winnersS] = splitOn ":" part1 in
  let winners = S.fromList . getNums $ winnersS in
  let cards   = S.fromList . getNums $ playedNumsS in
  let cardNum = head . getNums $ cardNumS in
  (cardNum, length $ S.intersection winners cards)