Advent of Code 2021
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module Day10_1 where
import System.IO (openFile, IOMode (ReadMode), hClose, hGetContents)
import Data.Maybe (mapMaybe)
import Data.List (sort)
closing :: Char -> Char
closing '(' = ')'
closing '[' = ']'
closing '{' = '}'
closing '<' = '>'
score :: Char -> Int
score ')' = 1
score ']' = 2
score '}' = 3
score '>' = 4
matchBraces :: [Char] -> [Char] -> Maybe [Char]
matchBraces [] [] = Nothing
matchBraces acc [] = Just acc
matchBraces acc (x:xs)
| x `elem` ['(', '[', '{', '<'] = matchBraces (closing x : acc) xs
| x == head acc = matchBraces (tail acc) xs
| otherwise = Nothing
main :: IO ()
main = do
input <- openFile "inputs/10.txt" ReadMode
contents <- hGetContents input
let routes = lines contents
print . (\x -> x !! (length x `div` 2)) . sort $ map (foldl (\acc x -> score x + (acc * 5)) 0) $ mapMaybe (matchBraces []) routes
hClose input