55 lines
1.6 KiB
Haskell
55 lines
1.6 KiB
Haskell
-- requires cabal install --lib megaparsec parser-combinators heap vector
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module Main (main) where
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import Control.Monad (void, when)
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import Data.Bits
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import Data.Functor
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import qualified Data.List as L
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import qualified Data.Map as M
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import Data.Maybe
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import Data.Ord (comparing)
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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 = 37327623
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type Input = [Int]
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type Parser = Parsec Void String
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parseInput' :: Parser Input
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parseInput' = some (read <$> some digitChar <* eol) <* 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 (nextN 2000) input
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where
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nextN :: Int -> Int -> Int
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nextN 0 n = n
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nextN i n = nextN (i-1) $ next n
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next :: Int -> Int
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next s = let s' = prune $ mix (shift s 6) s
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s'' = prune $ mix (shift s' (-5)) s'
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s''' = prune $ mix (shift s'' 11) s''
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in s'''
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mix :: Int -> Int -> Int
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mix = xor
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prune :: Int -> Int
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prune n = n `mod` 16777216
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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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