Amneesh Singh
38201248c4
not the cleanest, im still learning parsing in hs Signed-off-by: Amneesh Singh <natto@weirdnatto.in>
45 lines
1.6 KiB
Haskell
45 lines
1.6 KiB
Haskell
import Data.Char (isDigit)
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import Data.List (transpose)
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import Data.Maybe (catMaybes)
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import Text.ParserCombinators.ReadP
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main :: IO ()
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main = do
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input <- lines <$> readFile "day5.in"
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let (crates, cmds) = break null input
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let cratesList = map catMaybes $ transpose $ map (fst . last . readP_to_S parseCrates) $ init crates
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let cmdsList = map ((\(n, a, b) -> (n, a - 1, b - 1)) . fst . last . readP_to_S parseCmd) $ tail cmds
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print cratesList
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putStr "Q1: "
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print $ q1 cratesList cmdsList
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putStr "Q2: "
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print $ q2 cratesList cmdsList
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q1, q2 :: [[Char]] -> [(Int, Int, Int)] -> [Char]
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q1 crates cmds = map head $ foldl (\x xs -> moveCrates x xs True) crates cmds
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q2 crates cmds = map head $ foldl (\x xs -> moveCrates x xs False) crates cmds
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-- Computers are fast, really, not optimising right now
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moveCrates :: [[Char]] -> (Int, Int, Int) -> Bool -> [[Char]]
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moveCrates crates (n, a, b) rev =
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let (head, tail) = splitAt n $ crates !! a
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in replace b (replace a crates tail) ((if rev then reverse head else head) ++ crates !! b)
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where
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replace :: Int -> [a] -> a -> [a]
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replace i xs x = take i xs ++ [x] ++ drop (i + 1) xs
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parseCrates :: ReadP [Maybe Char]
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parseCrates = sepBy parseRow (char ' ')
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where
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parseRow :: ReadP (Maybe Char)
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parseRow = (Just <$> (char '[' *> get <* char ']')) +++ (Nothing <$ string " ")
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parseCmd :: ReadP (Int, Int, Int)
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parseCmd =
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(,,) <$> (string "move " *> getInt)
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<*> (string " from " *> getInt)
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<*> (string " to " *> getInt)
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where
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getInt :: ReadP Int
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getInt = read <$> many1 (satisfy isDigit)
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