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-- requires cabal install --lib megaparsec parser-combinators
module Main (main) where
import Control.Monad (void, when)
import Data.Bits (clearBit, setBit)
import Data.List (foldl')
import Data.Map qualified as M
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
import System.Exit (die)
exampleExpectedOutput = 165
type Bits = [Maybe Bool]
data Op = Mask Bits| Mem Int Int
type Input = [Op]
type Parser = Parsec Void String
parseMask :: Parser Op
parseMask = do
void $ string "mask = "
bits <- some $ (char '1' *> (return $ Just True)) <|> (char '0' *> (return $ Just False)) <|> (char 'X' *> (return Nothing))
return $ Mask bits
parseMem :: Parser Op
parseMem = do
void $ string "mem["
index <- some digitChar
void $ string "] = "
value <- some digitChar
return $ Mem (read index) (read value)
parseOps :: Parser Input
parseOps = do
ops <- some $ (parseMask <|> parseMem) <* (optional $ char '\n')
void $ eof
return $ ops
parseInput :: String -> IO Input
parseInput filename = do
input <- readFile filename
case runParser parseOps filename input of
Left bundle -> die $ errorBundlePretty bundle
Right ops -> return ops
computeValue :: Int -> Bits -> Int
computeValue value bits = fst $ foldl' evalBit (value, 35) bits
where
evalBit :: (Int, Int) -> Maybe Bool -> (Int, Int)
evalBit (value, index) (Just True) = (setBit value index, index-1)
evalBit (value, index) (Just False) = (clearBit value index, index-1)
evalBit (value, index) Nothing = (value, index-1)
compute :: Input -> Int
compute = extract . foldl' compute init
where
extract :: (M.Map Int Int, Bits) -> Int
extract = sum . M.elems . fst
compute :: (M.Map Int Int, Bits) -> Op -> (M.Map Int Int, Bits)
compute (acc, _) (Mask bits) = (acc, bits)
compute (acc, bits) (Mem index value) = (M.insert index (computeValue value bits) acc, bits)
init :: (M.Map Int Int, Bits)
init = (M.empty, [])
main :: IO ()
main = do
example <- parseInput "example"
let exampleOutput = compute example
when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
input <- parseInput "input"
print $ compute input
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