77 lines
2.4 KiB
Haskell
77 lines
2.4 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Bits (clearBit, setBit)
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import Data.List (foldl')
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import Data.Map qualified as M
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import System.Exit (die)
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exampleExpectedOutput = 208
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type Bits = [Maybe Bool]
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data Op = Mask Bits| Mem Int Int
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type Input = [Op]
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type Parser = Parsec Void String
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parseMask :: Parser Op
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parseMask = do
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void $ string "mask = "
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bits <- some $ (char '1' *> (return $ Just True)) <|> (char '0' *> (return $ Just False)) <|> (char 'X' *> (return Nothing))
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return $ Mask bits
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parseMem :: Parser Op
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parseMem = do
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void $ string "mem["
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index <- some digitChar
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void $ string "] = "
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value <- some digitChar
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return $ Mem (read index) (read value)
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parseOps :: Parser Input
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parseOps = do
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ops <- some $ (parseMask <|> parseMem) <* (optional $ char '\n')
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void $ eof
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return $ ops
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseOps filename input of
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Left bundle -> die $ errorBundlePretty bundle
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Right ops -> return ops
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computeOp :: Int -> Bits -> [Int]
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computeOp index bits = fst $ foldl' evalBit ([index], 35) bits
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where
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evalBit :: ([Int], Int) -> Maybe Bool -> ([Int], Int)
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evalBit (acc, bit) (Just False) = (acc, bit-1)
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evalBit (acc, bit) (Just True) = (map (\x -> setBit x bit) acc, bit-1)
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evalBit (acc, bit) Nothing = ((map (\x -> setBit x bit) acc) ++ (map (\x -> clearBit x bit) acc), bit-1)
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compute :: Input -> Int
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compute = extract . foldl' compute init
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where
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extract :: (M.Map Int Int, Bits) -> Int
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extract = sum . M.elems . fst
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compute :: (M.Map Int Int, Bits) -> Op -> (M.Map Int Int, Bits)
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compute (acc, _) (Mask bits) = (acc, bits)
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compute (acc, bits) (Mem index value) = (newAcc, bits)
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where
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newAcc :: M.Map Int Int
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newAcc = foldl' eval acc (computeOp index bits)
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eval :: M.Map Int Int -> Int -> M.Map Int Int
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eval acc' index' = M.insert index' value acc'
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init :: (M.Map Int Int, Bits)
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init = (M.empty, [])
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main :: IO ()
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main = do
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example <- parseInput "example2"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (die $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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