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author | Julien Dessaux | 2023-03-16 21:43:55 +0100 |
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committer | Julien Dessaux | 2023-03-16 21:43:55 +0100 |
commit | 6125f7357d2e6f7637580a1037da90b8535f9eeb (patch) | |
tree | 2cc536423ce25fcb96e133f3e575fa345c1ce154 /2020/08-Handheld_Halting/first.hs | |
parent | 2020-07 in haskell (diff) | |
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2020-08 in haskell
Diffstat (limited to '2020/08-Handheld_Halting/first.hs')
-rw-r--r-- | 2020/08-Handheld_Halting/first.hs | 57 |
1 files changed, 57 insertions, 0 deletions
diff --git a/2020/08-Handheld_Halting/first.hs b/2020/08-Handheld_Halting/first.hs new file mode 100644 index 0000000..3d01106 --- /dev/null +++ b/2020/08-Handheld_Halting/first.hs @@ -0,0 +1,57 @@ +-- 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 |