Data update

Task/Duffinian-numbers/Haskell/duffinian-numbers.hs

@@ -0,0 +1,50 @@
+import Data.List ( tail )
+import qualified Data.Set as S
+import Data.List.Split ( divvy )
+
+divisors :: Int -> [Int]
+divisors n = [d | d <- [1..n] , mod n d == 0]
+
+primeFactors :: Int -> [Int]
+primeFactors n = snd $ until ( (== 1 ) . fst ) step (n , [] )
+   where
+      step :: (Int , [Int]) -> (Int , [Int])
+      step ( aNumber , factors ) = ( div aNumber smallest , factors ++
+        [smallest] )
+        where
+          smallest :: Int
+          smallest = head $ tail $ divisors aNumber
+
+isRelativelyPrime :: Int -> Int -> Bool
+isRelativelyPrime a b = S.null $ S.intersection ( S.fromList $
+ primeFactors a ) ( S.fromList $ primeFactors b )
+
+isDuffinian :: Int -> Bool
+isDuffinian n = and [(length $ primeFactors n ) > 1 , isRelativelyPrime
+ ( sum $ divisors n ) n]
+
+solution :: [Int]
+solution = take 50 $ filter isDuffinian [1..]
+
+findTriplets :: [[Int]]
+findTriplets = take 15 $ filter condition $ divvy 3 1 $ filter
+ isDuffinian [1..]
+  where
+   condition :: [Int] -> Bool
+   condition [a , b , c] = b == a + 1 && c == b + 1
+
+outputTriplet :: [Int] -> String
+outputTriplet [a , b , c] = "(" ++ replicate ( 6 - length sa ) ' ' ++
+ sa ++ replicate (6 - length sb) ' ' ++ sb ++ replicate (6 - length sc )
+ ' ' ++ sc ++ "   )"
+   where
+      sa = show a
+      sb = show b
+      sc = show c
+
+main :: IO ( )
+main = do
+   putStrLn "The first 50 Duffinian numbers are :"
+   print solution
+   putStrLn "The first 15 Duffinian triplets are:"
+   mapM_ (\t -> putStrLn $ outputTriplet t ) findTriplets