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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.Functor
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 = 281
type Input = [(Int, Int)]
type Parser = Parsec Void String
parseDigit :: Parser Int
parseDigit = (C.digitToInt <$> digitChar)
<|> (string "one" $> 1)
<|> (string "two" $> 2)
<|> (string "three" $> 3)
<|> (string "four" $> 4)
<|> (string "five" $> 5)
<|> (string "six" $> 6)
<|> (string "seven" $> 7)
<|> (string "eight" $> 8)
<|> (string "nine" $> 9)
<|> (letterChar *> parseDigit)
parseDigitReversed :: Parser Int
parseDigitReversed = (C.digitToInt <$> digitChar)
<|> (string "eno" $> 1)
<|> (string "owt" $> 2)
<|> (string "eerht" $> 3)
<|> (string "ruof" $> 4)
<|> (string "evif" $> 5)
<|> (string "xis" $> 6)
<|> (string "neves" $> 7)
<|> (string "thgie" $> 8)
<|> (string "enin" $> 9)
<|> (letterChar *> parseDigitReversed)
parseFirstAndLast :: String -> (Int, Int)
parseFirstAndLast str = (f, l)
where
f = case runParser parseDigit "parseDigit" str of
Left bundle -> error $ errorBundlePretty bundle
Right input' -> input'
l = case runParser parseDigitReversed "parseDigit" (reverse str) of
Left bundle -> error $ errorBundlePretty bundle
Right input' -> input'
parseInput' :: Parser Input
parseInput' = fmap parseFirstAndLast <$> 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 -> (Int, Int) -> Int
process acc l = acc + fst l * 10 + snd l
compute :: Input -> Int
compute = L.foldl' process 0
main :: IO ()
main = do
example <- parseInput "example2"
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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