53 lines
1.6 KiB
Haskell
53 lines
1.6 KiB
Haskell
module Puzzles.Day1 (puzzle) where
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import Pre
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puzzle :: Puzzle
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puzzle =
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Puzzle
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{ number = 1
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, parser = const $ ((,) <$> ((char 'L' $> L) <|> (char 'R' $> R)) <*> (Inc <$> decimal)) `sepEndBy` newline
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, parts =
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( sum
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. ( flip evalState 50
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. traverse \(d, i) -> do
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modify $ snd . step i d
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p' <- get
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pure $ Count if p' == 0 then 1 else 0
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)
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)
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/\ ( sum
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. flip evalState 50
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. traverse \(d, i) -> do
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p <- get
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c <- state $ step i d
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p' <- get
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pure case d of
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R -> abs c
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L ->
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if
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| p == 0 -> abs c - 1
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| p' == 0 -> abs c + 1
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| otherwise -> abs c
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)
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/\ nil
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, extraTests = mempty
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}
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data Direction = L | R
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deriving (Eq, Ord, Show, Generic, NFData)
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newtype Pos = Pos Int
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deriving newtype (Eq, Ord, Show, Num, NFData)
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newtype Inc = Inc Int
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deriving newtype (Eq, Ord, Show, Num, NFData)
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newtype Count = Count Int
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deriving newtype (Eq, Ord, Show, Num, NFData)
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step :: Inc -> Direction -> Pos -> (Count, Pos)
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step (Inc i) d (Pos p) = bimap Count Pos case d of
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L -> (p - i) `divMod` 100
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R -> (p + i) `divMod` 100
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