71 lines
1.7 KiB
Haskell
71 lines
1.7 KiB
Haskell
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module Day8 where
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import Data.Array
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import Data.Char
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import qualified Data.Set as S
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import Text.ParserCombinators.ReadP
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signedInt :: ReadP Int
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signedInt = do
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sign <- char '+' <++ char '-'
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digits <- munch1 isDigit
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return $ value sign digits
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where
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value '+' = read
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value '-' = negate . read
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data Inst = Acc Int | Jmp Int | Nop Int
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deriving (Show)
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inst :: ReadP Inst
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inst = do
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op <- choice $ map string ["acc", "jmp", "nop"]
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_ <- skipSpaces
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arg <- signedInt
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return $ case op of
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"acc" -> Acc arg
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"jmp" -> Jmp arg
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"nop" -> Nop arg
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type Program = Array Int Inst
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program :: ReadP Program
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program = do
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insts <- inst `sepBy` char '\n'
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_ <- skipSpaces
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_ <- eof
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let bnds = (0, length insts - 1)
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return $ listArray bnds insts
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parse p s = unwrap $ readP_to_S p s
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where
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unwrap [(a, "")] = a
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unwrap [(_, rs)] = error "Parser did not consume entire stream."
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unwrap (a:as) = unwrap as
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unwrap _ = error "Parser error"
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data State = State { acc :: Int, sp :: Int, visits :: S.Set Int, looped :: Bool }
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deriving (Show)
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start = State 0 0 S.empty False
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outOfBounds arr idx = idx < l || idx > r
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where (l, r) = bounds arr
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run pgrm = run' pgrm start
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run' pgrm state
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| outOfBounds pgrm $ sp state = state
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| S.member (sp state) (visits state) = State (acc state) (sp state) (visits state) True
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| otherwise = run' pgrm state'
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where
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state' = State acc' sp' visits' False
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inst = pgrm ! (sp state)
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acc' = case inst of
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(Acc arg) -> (acc state + arg)
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_ -> acc state
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sp' = case inst of
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(Jmp arg) -> (sp state + arg)
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_ -> (sp state + 1)
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visits' = S.insert (sp state) (visits state)
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