> From: Richard O'Keefe [mailto:o...@cs.otago.ac.nz] > > These lines of Haskell code find the Zumkeller numbers up to 5000 > in 5 seconds on a 2.2GHz intel Mac. The equivalent in SML took > 1.1 seconds. Note that this just finds whether a suitable > partition exists; it does not report the partition. > > factors :: Int -> [Int] > > factors n = [m | m <- [1..n], mod n m == 0] > > can_part :: [Int] -> Int -> Bool > > can_part _ 0 = True > can_part xs t = loop xs [] > where loop [] _ = False > loop (x:xs) ys = x <= t && can_part (xs++ys) (t-x) > || loop xs ys > > is_Zumkeller :: Int -> Bool > is_Zumkeller n = > let facs = factors n > fsum = sum facs > in mod fsum 2 == 0 && > can_part facs (div fsum 2) > > main = print (filter is_Zumkeller [1..5000])
Thanks, I like this solution! Pure functional, easy to understand, no monads and fast :-) -- Frank Buss, f...@frank-buss.de http://www.frank-buss.de, http://www.it4-systems.de _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
