AOC 2023 Day 1

day_one_2023.hs

module DayOne
    ( partOne, decodeLine, substringIndices, Digit (..), operateOnString, toLower, allDigits, firstDigit, lastDigit, scoreDigit, scoreLine, partTwo
    ) where


import qualified Data.Text as T
import qualified Data.Text.IO as TI
import qualified Data.Maybe as M
import qualified Data.List as L
import qualified Data.List.Safe as LS


-- ############# Data Structures ##############
data Digit = Zero | One | Two | Three | Four | Five | Six | Seven | Eight | Nine deriving (Show, Enum, Eq)

allDigits = enumFrom Zero
scoreDigit d = M.fromJust $ L.elemIndex d allDigits
-- #############################################


toLower = operateOnString T.toLower
operateOnString f = T.unpack . f . T.pack

substringIndices target world = go world 0
  where go "" _ = []
        go remainingWorld currentIndex =
          if L.isPrefixOf target remainingWorld
            then currentIndex : go (tail remainingWorld) (currentIndex + 1)
            else go (tail remainingWorld) (currentIndex + 1)


hitIndices :: Digit -> String -> [Int]
hitIndices target world = fullNameIndices ++ numeralIndices
  where fullNameIndices = substringIndices (toLower (show target)) world
        numeralIndices = substringIndices (toLower (show (scoreDigit target))) world

firstDigit :: String -> Maybe Digit
firstDigit s = LS.minimumBy score allDigits
  where score a b = myCompare (hitIndices a s) (hitIndices b s)
        myCompare [] [] = EQ
        myCompare [] _ = GT
        myCompare _ [] = LT
        myCompare a b = compare (L.minimum a) (L.minimum b)


lastDigit :: String -> Maybe Digit
lastDigit s = LS.maximumBy score allDigits
  where score a b = compare maxLeftHit maxRightHit
          where maxLeftHit :: Maybe Int = (LS.maximum (hitIndices a s))
                maxRightHit :: Maybe Int = (LS.maximum (hitIndices b s))

scoreLine :: String -> Int
scoreLine line = read $ map (head . show. scoreDigit) $ M.catMaybes [firstDigit line, lastDigit line]

partTwo :: IO ()
partTwo = do
  fileBody <- TI.readFile "/users/wailee.feman/Downloads/input.txt"
  let allLines = T.lines fileBody
      ints = map (scoreLine . T.unpack) allLines
      answer = sum ints
  print answer


-- part 1
partOne :: IO ()
partOne = do
  fileBody <- TI.readFile "/users/wailee.feman/Downloads/input.txt"
  let allLines = T.lines fileBody
      ints = map (decodeLine . T.unpack) allLines
      answer = sum ints
  print answer



decodeLine :: String -> Int
decodeLine s = read [firstDigit, lastDigit]
  where firstDigit = head digits
        lastDigit = last digits
        digits :: String
        digits = filter isDigit s
        isDigit :: Char -> Bool
        isDigit c = elem c allDigitsString
        allDigitsString :: String
        allDigitsString = enumFromTo '0' '9'