Time for an 2014 update…

Task/Parallel-calculations/Haskell/parallel-calculations-1.hs

@@ -1,8 +1,9 @@
-import Control.Parallel.Strategies
+mport Control.Parallel.Strategies
 import Control.DeepSeq
 import Data.List
 import Data.Function
 
+nums :: [Integer]
 nums = [112272537195293
        ,112582718962171
        ,112272537095293
@@ -10,21 +11,20 @@ nums = [112272537195293
        ,115797840077099
        ,1099726829285419]
 
-factors :: Integral a => a -> [a]
-factors n | n `rem` 2 == 0 = [2] ++ factors (n `quot` 2)
-          | otherwise      = y
-  where y = [x | x <- [3,5..ceiling . sqrt $ fromIntegral n]
-            ++ [n], n `rem` x == 0]
+lowestFactor :: Integral a => a -> a -> a
+lowestFactor s n | n `rem` 2 == 0 = 2
+                 | otherwise      = head $ y
+  where y = [x | x <- [s..ceiling . sqrt $ fromIntegral n]
+            ++ [n], n `rem` x == 0, x `rem` 2 /= 0]
 
-minPrimes :: [Integer] -> (Integer, [Integer])
-minPrimes ns = (\(x, y) -> (x, y:factors ( x `quot` y))) $
-              maximumBy (compare `on` snd)
-              (zip ns (parMap rdeepseq (head . factors) ns))
+primeFactors l n = f n l []
+    where f n l xs = if n > 1 then f (n `div` l) (lowestFactor (max l 3)  (n `div` l)) (l:xs)
+                              else xs
+
+minPrimes ns = (\(x,y) -> (x,primeFactors y x)) $
+              maximumBy (compare `on` snd) $
+              zip ns (parMap rdeepseq (lowestFactor 3) ns)
 
 main :: IO ()
 main = do
-        putStrLn . concat $ ["The number with the "
-                            , "largest minimum prime factor was:\n"
-                            , show x, "\nWith factors: "]
-        mapM_ print y
-  where (x, y) =  (minPrimes nums)
+    print $ minPrimes nums