13 lines
610 B
Haskell
13 lines
610 B
Haskell
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-- 3 - largest prime factor
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-- problem_3 :: Integer -> Integer
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prims = fix (\f (x:xs) -> x:f (filter (\y -> rem y x /= 0) xs)) [2..]
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get_prims :: Integer -> [Integer]
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get_prims 1 = []
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get_prims n = let p = head $ dropWhile (\x -> rem n x /= 0) prims
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in p:get_prims (div n p)
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--next_prim xs = head $ dropWhile (\y -> any (\e -> rem y e == 0) xs) [last xs + 1..]
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--prims = filter (\x -> not $ any (\n -> rem x n == 0) [2..(x-1)]) [1..]
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--pfactors n = [x | x <- takeWhile (\y -> y*y <= n) [2..], n `mod` x == 0, null $ pfactors x]
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problem_3 :: Integer -> Integer
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problem_3 x = last $ get_prims x
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