28 lines
739 B
Haskell
28 lines
739 B
Haskell
import Data.List (find, group)
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import Data.Maybe (fromJust)
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firstPrimeFactor :: Int -> Int
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firstPrimeFactor n = head $ filter ((0 ==) . mod n) [2 .. n]
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allPrimeFactors :: Int -> [Int]
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allPrimeFactors 1 = []
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allPrimeFactors n =
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let first = firstPrimeFactor n
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in first : allPrimeFactors (n `div` first)
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factorCount :: Int -> Int
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factorCount 1 = 1
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factorCount n = product ((succ . length) <$> group (allPrimeFactors n))
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divisorCount :: Int -> (Int, Int)
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divisorCount = (,) <*> factorCount
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hcnNext :: (Int, Int) -> (Int, Int)
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hcnNext (num, factors) =
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fromJust $ find ((> factors) . snd) (divisorCount <$> [num ..])
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hcnSequence :: [Int]
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hcnSequence = fst <$> iterate hcnNext (1, 1)
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main :: IO ()
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main = print $ take 20 hcnSequence
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