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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.Char qualified as C
import Data.List qualified as L
import Data.Map qualified as M
import Data.Maybe
import Data.Set qualified as S
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
exampleExpectedOutput = 142
type Input = [String]
type Parser = Parsec Void String
parseInput' :: Parser Input
parseInput' = some (some alphaNumChar <* eol) <* eof
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseInput' filename input of
Left bundle -> error $ errorBundlePretty bundle
Right input' -> return input'
process :: Int -> String -> Int
process acc str = acc + f * 10 + l
where
f = C.digitToInt . head $ dropWhile C.isLetter str
l = C.digitToInt . head . dropWhile C.isLetter $ reverse str
compute :: Input -> Int
compute = L.foldl' process 0
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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