70 lines
1.9 KiB
Haskell
70 lines
1.9 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Applicative.Permutations
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import Control.Monad (void, when)
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import Data.Char qualified as C
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import Data.Either
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import Data.Functor
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import Data.List qualified as L
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import Data.Map qualified as M
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import Data.Maybe
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import Data.Set qualified as S
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import Data.Vector qualified as V
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import Data.Void (Void)
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import Text.Megaparsec
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import Text.Megaparsec.Char
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import Debug.Trace
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exampleExpectedOutput = 136
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data Tile = Cube | Empty | Round deriving (Eq)
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instance Show Tile where
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show Cube = "#"
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show Empty = "."
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show Round = "O"
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type Row = [Tile]
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type Input = [Row]
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type Parser = Parsec Void String
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parseTile :: Parser Tile
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parseTile = char '#' $> Cube
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<|> char '.' $> Empty
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<|> char 'O' $> Round
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parseRow :: Parser Row
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parseRow = some parseTile <* eol
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parseInput' :: Parser Input
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parseInput' = some parseRow <* eof
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parseInput :: String -> IO Input
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parseInput filename = do
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input <- readFile filename
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case runParser parseInput' filename input of
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Left bundle -> error $ errorBundlePretty bundle
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Right input' -> return input'
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compute :: Input -> Int
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compute input = sum $ map (fst . L.foldr weight (0, 1)) shiftedInput
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where
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transposedInput = L.transpose input
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shiftedInput = map (shift 0) transposedInput
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shift :: Int -> Row -> Row
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shift n [] = replicate n Empty
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shift n (Cube:xs) = replicate n Empty ++ Cube : shift 0 xs
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shift n (Empty:xs) = shift (n+1) xs
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shift n (Round:xs) = Round : shift n xs
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weight :: Tile -> (Int, Int) -> (Int, Int)
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weight Round (acc, i) = (acc + i, i+1)
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weight _ (acc, i) = (acc, i+1)
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main :: IO ()
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main = do
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example <- parseInput "example"
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let exampleOutput = compute example
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when (exampleOutput /= exampleExpectedOutput) (error $ "example failed: got " ++ show exampleOutput ++ " instead of " ++ show exampleExpectedOutput)
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input <- parseInput "input"
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print $ compute input
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