AOC 2023 Day Four

day_four_2023.hs

{-# LANGUAGE OverloadedStrings #-}
module DayFour (module DayFour) where

import qualified Data.Text as T
import qualified Text.Read as TR
import qualified Data.Maybe as M
import qualified Data.Set as S


extractNumbers :: T.Text -> [Int]
extractNumbers text = M.catMaybes $ Prelude.map (TR.readMaybe . T.unpack) $ T.split (== ' ') text

targetNumbers card = extractNumbers firstHalf
  where [firstHalf, _] = T.split (== '|') card

receivedNumbers card = extractNumbers secondHalf
  where [_, secondHalf] = T.split (== '|') card

hitCount card = length intersections
  where intersections = (S.fromList $ targetNumbers  card) `S.intersection` (S.fromList $ receivedNumbers card)

scoreCard card
  | (hitCount card) > 0 = 2 ^ ((hitCount card) - 1)
  | otherwise = 0

partOne lines = sum $ map scoreCard lines

cardNumber card = head $ extractNumbers $ T.filter (/= ':') card

sampleInput :: [T.Text]
sampleInput = ["Card 1: 41 48 83 86 17 | 83 86  6 31 17  9 48 53",
            "Card 2: 13 32 20 16 61 | 61 30 68 82 17 32 24 19",
            "Card 3:  1 21 53 59 44 | 69 82 63 72 16 21 14  1",
            "Card 4: 41 92 73 84 69 | 59 84 76 51 58  5 54 83",
            "Card 5: 87 83 26 28 32 | 88 30 70 12 93 22 82 36",
            "Card 6: 31 18 13 56 72 | 74 77 10 23 35 67 36 11"]

slowResolve _ [] = []
slowResolve world (current:rest) = current : (slowResolve world (rest ++ earned))
  where earned = map cardAt neededCardIndices
        score = hitCount current
        currentCardNumber = cardNumber current
        neededCardIndices = (currentCardNumber + 1) `enumFromTo` (currentCardNumber + score)
        cardAt idx = world !! (idx - 1)


buildUpAnswer builtSoFar [] = builtSoFar
buildUpAnswer builtSoFar (current:rest) = buildUpAnswer newBuilt rest
  where newBuilt = myScore:builtSoFar
        myScore = 1 + (sum $ map (builtSoFar !!) neededCardIndices)
        score = hitCount current
        neededCardIndices = 0 `enumFromTo` (score - 1)

partTwo cards = sum $ buildUpAnswer [] $ reverse cards