67 lines
2 KiB
Haskell
67 lines
2 KiB
Haskell
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-- requires cabal install --lib megaparsec parser-combinators
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module Main (main) where
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import Control.Monad (void, when)
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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 (fromJust)
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import Data.Set qualified as S
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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 System.Exit (die)
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exampleExpectedOutput = 67384529
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type Cup = Int
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type Input = [Cup]
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type History = [Input]
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type Parser = Parsec Void String
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parseCup :: Parser Cup
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parseCup = do
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n <- digitChar
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return $ read [n] - 1 -- so that there is a 0 in there and then we can use modulo
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parseInput' :: Parser Input
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parseInput' = some parseCup <* optional (char '\n') <* 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 -> die $ errorBundlePretty bundle
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Right input' -> return input'
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score :: Input -> Int
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score (0:xs) = read . concat $ map (\i -> show (i+1)) xs
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score (x:xs) = score $ xs ++ [x]
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compute' :: Input -> Int -> Int
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compute' input 0 = score input
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compute' (current:one:two:three:xs) remainingMoves = compute' step (remainingMoves - 1)
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where
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l = length xs + 4
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destinationIndex :: Int
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destinationIndex = case L.elemIndex ((current - 1) `mod` l) xs of
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Just i -> i
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Nothing -> case L.elemIndex ((current - 2) `mod` l) xs of
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Just i -> i
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Nothing -> case L.elemIndex ((current - 3) `mod` l) xs of
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Just i -> i
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Nothing -> fromJust $ L.elemIndex ((current - 4) `mod` l) xs
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destinationIndex' = destinationIndex + 1
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step :: Input
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step = concat [take destinationIndex' xs, [one, two, three], drop destinationIndex' xs, [current]]
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compute :: Input -> Int
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compute input = compute' input 100
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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) (die $ "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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