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-- requires cabal install --lib megaparsec parser-combinators heap vector
module Main (main) where
import Control.Monad (void, when)
import Data.Bits
import Data.Functor
import qualified Data.List as L
import Data.Void (Void)
import Text.Megaparsec
import Text.Megaparsec.Char
exampleExpectedOutput = "4,6,3,5,6,3,5,2,1,0"
type Register = Int
type Op = Int
data Input = Input [Register] [Op] deriving Show
type Parser = Parsec Void String
parseNumber :: Parser Int
parseNumber = read <$> some digitChar
parseRegister :: Parser Register
parseRegister = string "Register " *> (char 'A' <|> char 'B' <|> char 'C') *> string ": " *> parseNumber
parseInput' :: Parser Input
parseInput' = Input <$> some (parseRegister <* eol) <* eol
<*> (string "Program: " *> some (parseNumber <* optional (char ',')) <* 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'
type Pointer = Int
type PState = (Pointer, [Register], [Int])
compute :: Input -> String
compute (Input start ops) = L.intercalate "," . L.reverse . map show . (\(_, _, s) -> s) $ step (0, start, [])
where
end = length ops
step :: PState -> PState
step ps@(p, [a, b, c], _) | p == end = ps
| otherwise = step $ i ps co
where
i = [adv, bxl, bst, jnz, bxc, out, bdv, cdv] L.!! (ops L.!! p)
co = [0, 1, 2, 3, a, b, c] L.!! (ops L.!! (p+1))
adv (p, [a, b, c], acc) n = (p+2, [a `div` (2 ^ n), b, c], acc)
bxl (p, [a, b, c], acc) n = (p+2, [a, xor b n, c], acc)
bst (p, [a, b, c], acc) n = (p+2, [a, n `mod` 8, c], acc)
jnz (p, [0, b, c], acc) n = (p+2, [0, b, c], acc)
jnz (p, [a, b, c], acc) n = (n, [a, b, c], acc)
bxc (p, [a, b, c], acc) _ = (p+2, [a, xor b c, c], acc)
out (p, [a, b, c], acc) n = (p+2, [a, b, c], (n `mod` 8) : acc)
bdv (p, [a, b, c], acc) n = (p+2, [a, a `div` (2 ^ n), c], acc)
cdv (p, [a, b, c], acc) n = (p+2, [a, b, a `div` (2 ^ n)], acc)
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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