77 lines
2.7 KiB
Haskell
77 lines
2.7 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Bits
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import Data.Functor
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import qualified Data.List as L
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import Data.Maybe
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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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type Register = Int
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type Op = Int
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data Input = Input [Register] [Op] deriving Show
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type Parser = Parsec Void String
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parseNumber :: Parser Int
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parseNumber = read <$> some digitChar
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parseRegister :: Parser Register
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parseRegister = string "Register " *> (char 'A' <|> char 'B' <|> char 'C') *> string ": " *> parseNumber
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parseInput' :: Parser Input
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parseInput' = Input <$> some (parseRegister <* eol) <* eol
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<*> (string "Program: " *> some (parseNumber <* optional (char ',')) <* eol <* eof)
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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 parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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type Pointer = Int
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type PState = (Pointer, [Register], [Int])
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compute :: Input -> Int
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compute (Input start ops) = minimum $ findA 0 (tail $ L.reverse $ L.tails ops)
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where
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findA :: Int -> [[Int]] -> [Int]
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findA a [] = [a]
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findA a (l:ls) = concatMap (\next -> findA next ls) nexts
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where
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candidates :: [Int]
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candidates = [a*8..a*8+7]
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steps :: [PState]
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steps = map (\x -> step (0, [x, 0, 0], [])) candidates
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outputs :: [[Int]]
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outputs = map (\(_, [_, _, _], x') -> reverse x') steps
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valids :: [Int]
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valids = L.elemIndices l outputs
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nexts :: [Int]
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nexts = map (candidates L.!!) valids
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end = length ops
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step :: PState -> PState
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step ps@(p, [a, b, c], _) | p == end = ps
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| otherwise = step $ i ps co
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where
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i = [adv, bxl, bst, jnz, bxc, out, bdv, cdv] L.!! (ops L.!! p)
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co = [0, 1, 2, 3, a, b, c] L.!! (ops L.!! (p+1))
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adv (p, [a, b, c], acc) n = (p+2, [a `div` (2 ^ n), b, c], acc)
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bxl (p, [a, b, c], acc) n = (p+2, [a, xor b n, c], acc)
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bst (p, [a, b, c], acc) n = (p+2, [a, n `mod` 8, c], acc)
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jnz (p, [0, b, c], acc) n = (p+2, [0, b, c], acc)
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jnz (p, [a, b, c], acc) n = (n, [a, b, c], acc)
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bxc (p, [a, b, c], acc) _ = (p+2, [a, xor b c, c], acc)
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out (p, [a, b, c], acc) n = (p+2, [a, b, c], (n `mod` 8) : acc)
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bdv (p, [a, b, c], acc) n = (p+2, [a, a `div` (2 ^ n), c], acc)
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cdv (p, [a, b, c], acc) n = (p+2, [a, b, a `div` (2 ^ n)], acc)
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main :: IO ()
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main = do
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input <- parseInput "input"
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print $ compute input
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