25 lines
674 B
Haskell
25 lines
674 B
Haskell
module ProjectEuler
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( isPrime
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, digitSum
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, sumProperDivisors
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) where
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import Data.Char (digitToInt)
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isPrime :: (Integral n) => n -> Bool
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isPrime 1 = False
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isPrime 2 = True
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isPrime 3 = True
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isPrime n =
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n `mod` 2 /= 0 && n `mod` 3 /= 0 && null [ x | x <- candidates, n `mod` x == 0 || n `mod` (x+2) == 0 ]
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where candidates = [5,11..limit]
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limit = floor(sqrt(fromIntegral n)) + 1
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digitSum :: (Integral a, Show a) => a -> Int
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digitSum n = sum $ map digitToInt $ show n
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sumProperDivisors :: (Integral a) => a -> a
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sumProperDivisors n = sum [ if x /= y then x + y else x | x <- [2..ceiling $ sqrt $ fromIntegral n], let y = n `div` x, n `mod` x == 0 ] + 1
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