120 lines
4.2 KiB
Haskell
120 lines
4.2 KiB
Haskell
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{-# LANGUAGE FlexibleContexts #-}
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import AoC
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import Control.Applicative
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import Control.Monad
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import Control.Monad.ST
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import Control.Monad.Trans.Class
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import Control.Monad.Trans.Except
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import Control.Monad.Trans.Maybe
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import Data.Array.ST
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import Data.Maybe
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import Text.ParserCombinators.ReadP
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import Text.Read.Lex
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data Instruction = Nop Int | Acc Int | Jmp Int deriving (Show)
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data MemoryCell = MemoryCell { instruction :: Instruction
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, executed :: Bool
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}
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deriving (Show)
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type Memory s = STArray s Int MemoryCell
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data Machine s = Machine { pc :: Int
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, acc :: Int
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, memory :: Memory s
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}
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data RunError = OutOfRange | WouldLoop | Breakpoint deriving (Show)
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type MachineRunner s = Machine s -> ExceptT RunError (ST s) (Machine s)
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parseInstruction :: ReadP Instruction
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parseInstruction = choice [ Nop <$> parseIns "nop"
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, Acc <$> parseIns "acc"
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, Jmp <$> parseIns "jmp"
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]
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where parseIns name = string name >> char ' ' >> parseNumber
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parseNumber = do
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sign <- option '+' (choice $ map char $ "+-")
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num <- readDecP
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return $ case sign of
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'+' -> num
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'-' -> -num
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newMemory :: [Instruction] -> ST s (Memory s)
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newMemory insns = newListArray (0, length insns-1) $ [MemoryCell { instruction = ins, executed = False } | ins <- insns]
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newMachine :: [Instruction] -> ST s (Machine s)
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newMachine insns = do
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mem <- newMemory insns
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return $ Machine { pc = 0, acc = 0, memory = mem }
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stepMachine :: Machine s -> ST s (Machine s)
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stepMachine m = do
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cell <- readArray (memory m) (pc m)
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writeArray (memory m) (pc m) $ cell { executed = True }
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(pcF, accF) <- case instruction cell of
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Nop _ -> return ((+1), id)
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Acc i -> return ((+1), (+i))
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Jmp i -> return ((+i), id)
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let newPc = pcF $ pc m
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newAcc = accF $ acc m
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return $ m { pc = newPc, acc = newAcc }
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runUnless :: (Machine s -> MaybeT (ST s) RunError) -> MachineRunner s -> MachineRunner s
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runUnless p stepper m = do
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res <- lift $ runMaybeT $ p m
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case res of
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Nothing -> stepper m
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Just e -> throwE e
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breakOnLoop :: MachineRunner s -> MachineRunner s
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breakOnLoop = runUnless alreadyExecuted
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where alreadyExecuted m =
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do cell <- lift $ readArray (memory m) (pc m)
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unless (executed cell) empty
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return WouldLoop
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breakOnAddr :: Int -> MachineRunner s -> MachineRunner s
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breakOnAddr addr = runUnless $ fetchFrom addr
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where fetchFrom addr m =
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do unless (pc m == addr) empty
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return Breakpoint
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runUntilError :: MachineRunner s -> Machine s -> ST s (RunError, Int, Int)
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runUntilError step m = do
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result <- runExceptT $ step m
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case result of
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Right m' -> runUntilError step m'
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Left e -> return (e, (pc m), (acc m))
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part1 :: [Instruction] -> Int
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part1 is = fromJust $ runST $ runMaybeT $ do
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(WouldLoop, _, acc) <- lift $ newMachine is >>= runUntilError stepper
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return acc
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where stepper = breakOnLoop (lift . stepMachine)
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tryTerminate :: Machine s -> MaybeT (ST s) Int
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tryTerminate m = do
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breakpoint <- fmap (\(_, max) -> max + 1) $ lift $ getBounds (memory m)
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(Breakpoint, _, acc) <- lift $ runUntilError (stepper breakpoint) m
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return acc
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where stepper b = breakOnAddr b . breakOnLoop $ (lift . stepMachine)
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jmpNopFlips :: [Instruction] -> [[Instruction]]
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jmpNopFlips [] = []
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jmpNopFlips (x:xs) = case x of
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Jmp i -> (Nop i:xs) : rest
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Nop i -> (Jmp i:xs) : rest
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_ -> rest
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where rest = (x:) <$> jmpNopFlips xs
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part2 :: [Instruction] -> Int
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part2 instructions = fromJust $ msum $ runST $ mapM testInstructions possibleInstructions
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where testInstructions is = runMaybeT $ lift (newMachine is) >>= tryTerminate
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possibleInstructions = instructions : jmpNopFlips instructions
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main = runAoC (map (fromJust . oneCompleteResult parseInstruction) . lines) part1 part2
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