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taiansu/goldbach.hs

Last active May 12, 2018 11:07
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Flolac week of code 3: goldbach
Raw
goldbach.hs
goldbach :: Int -> Maybe(Int, Int)
goldbach n = search halfOfPrimes where
search [] = Nothing
search (x:xs) = if isPrime (n - x) then Just (x, n - x) else search xs
halfOfPrimes = 2 : [ x | x <- [3, 5..half], isPrime x]
half = div n 2
isPrime :: Int -> Bool
isPrime 2 = True
isPrime n = not $ any isFactor (2 : [3, 5 .. (square n)])
where square = floor . sqrt . fromIntegral
isFactor x = mod n x == 0
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