57 lines
1.6 KiB
Haskell
57 lines
1.6 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
|
|
module Main (main) where
|
|
import Control.Monad (void, when)
|
|
import qualified Data.Set as S
|
|
import Data.Void (Void)
|
|
import Text.Megaparsec
|
|
import Text.Megaparsec.Char
|
|
import System.Exit (die)
|
|
|
|
exampleExpectedOutput = 5
|
|
|
|
data Op = Nop Int | Acc Int | Jmp Int
|
|
|
|
type Parser = Parsec Void String
|
|
|
|
parseOp :: Parser Op
|
|
parseOp = do
|
|
op <- string "nop " <|> string "acc " <|> string "jmp "
|
|
sign <- (char '+' *> return 1) <|> (char '-' *> return (-1))
|
|
num <- some digitChar
|
|
void $ char '\n'
|
|
let n = sign * (read num)
|
|
return $ case op of
|
|
"nop " -> Nop n
|
|
"acc " -> Acc n
|
|
"jmp " -> Jmp n
|
|
|
|
parseOps :: Parser [Op]
|
|
parseOps = some parseOp <* eof
|
|
|
|
parseInput :: String -> IO [Op]
|
|
parseInput filename = do
|
|
input <- readFile filename
|
|
case runParser parseOps filename input of
|
|
Left bundle -> die $ errorBundlePretty bundle
|
|
Right ops -> return ops
|
|
|
|
compute :: [Op]-> Int
|
|
compute ops = run 0 0 S.empty
|
|
where
|
|
run :: Int -> Int -> S.Set Int -> Int
|
|
run pointer acc visited
|
|
| S.member pointer visited = acc
|
|
| otherwise = case ops !! pointer of
|
|
Nop _ -> run (pointer + 1) acc visited'
|
|
Acc i -> run (pointer + 1) (acc + i) visited'
|
|
Jmp i -> run (pointer + i) acc visited'
|
|
where
|
|
visited' = S.insert pointer visited
|
|
|
|
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
|