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shugo/collatz.hs

Created December 10, 2011 06:15
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Collatz sequence
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collatz.hs
collatz' :: Int -> Maybe (Int, Int)
collatz' 0 = Nothing
collatz' 1 = Just (1, 0)
collatz' n
| n `mod` 2 == 0 = Just (n, n `div` 2)
| otherwise = Just (n, 3 * n + 1)
collatz :: Int -> [Int]
collatz n = unfoldr collatz' n
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