26 lines
677 B
Haskell
26 lines
677 B
Haskell
#!/usr/bin/env stack
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-- stack --resolver lts-9.18 script
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{-# LANGUAGE BangPatterns #-}
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import Data.List
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rotate :: Int -> [a] -> [a]
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rotate n xs = take (length xs) (drop n (cycle xs))
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spinlock :: (Num a, Enum a) => a -> Int -> [a] -> [a]
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spinlock n steps buf = foldl' f buf [1..n]
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where f !curbuf !i = let !newbuf = rotate (steps+1) curbuf in i:newbuf
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valueAfter :: Eq t => t -> [t] -> t
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valueAfter n buf = buf !! ((i + 1) `rem` length buf)
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where Just i = elemIndex n buf
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main :: IO ()
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main = do
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let input = 312
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n = 2017
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start = [0]
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print $ valueAfter n $ spinlock n input start
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-- let n = 50000000
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-- print $ valueAfter 0 $ spinlock n input start
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