51 lines
1.8 KiB
Haskell
51 lines
1.8 KiB
Haskell
import qualified Data.Set as S
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import Data.List.Split ( chunksOf )
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divisors :: Int -> [Int]
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divisors n = [d | d <- [2 .. n] , mod n d == 0]
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--for obvious theoretical reasons the smallest divisor of a number bare 1
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--must be prime
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primeFactors :: Int -> [Int]
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primeFactors n = snd $ until ( (== 1) . fst ) step (n , [] )
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where
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step :: (Int , [Int] ) -> (Int , [Int] )
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step (n , li) = ( div n h , li ++ [h] )
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where
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h :: Int
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h = head $ divisors n
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primeDivisors :: Int -> [Int]
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primeDivisors n = S.toList $ S.fromList $ primeFactors n
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solution :: (Int -> [Int] ) -> [Int]
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solution f = snd $ until ( (== 30 ) . length . snd ) step ([2 , 3] , [] )
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where
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step :: ([Int] , [Int] ) -> ([Int] , [Int])
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step ( neighbours , ranums ) = ( map ( + 1 ) neighbours , if (sum $ f
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$ head neighbours ) == (sum $ f $ last neighbours) then
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ranums ++ [ head neighbours ] else ranums )
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formatNumber :: Int -> String -> String
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formatNumber width num
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|width > l = replicate ( width -l ) ' ' ++ num
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|width == l = num
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|width < l = num
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where
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l = length num
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main :: IO ( )
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main = do
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let ruth_aaron_pairs = solution primeFactors
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maxlen = length $ show $ last ruth_aaron_pairs
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numberlines = chunksOf 8 $ map show ruth_aaron_pairs
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ruth_aaron_divisors = solution primeDivisors
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maxlen2 = length $ show $ last ruth_aaron_divisors
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numberlines2 = chunksOf 8 $ map show ruth_aaron_divisors
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putStrLn "First 30 Ruth-Aaaron numbers ( factors ) :"
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mapM_ (\nlin -> putStrLn $ foldl1 ( ++ ) $ map (\st -> formatNumber (maxlen + 2) st )
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nlin ) numberlines
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putStrLn " "
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putStrLn "First 30 Ruth-Aaron numbers( divisors ):"
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mapM_ (\nlin -> putStrLn $ foldl1 ( ++ ) $ map (\st -> formatNumber (maxlen2 + 2) st )
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nlin ) numberlines2
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