User talk:Gaaijz

welcome!

Welcome to Rosetta Code! If you have any questions, drop them in the appropriate talk page, and someone will get back to you. If you have a more general question, try Mwn3d's or my talk pages. --Short Circuit 04:10, 2 September 2008 (UTC)

Jers

Hey Arie. This is Dan Bron from the J forums. Tracy Harms is here too. It's good to have J representation on RosettaCode. I'm glad you posted a J solution to the Pyramid of Numbers, that was near the top of my to do list. Have you considered posting a task along the lines of your Rabbit Sequence?

Oh, by the way, I linkified your user page. I hope you don't mind. Go ahead and revert it if you like it better the other way.

DanBron 13:48, 2 September 2008 (UTC)

Zigzag

Two different approaches with Haskell for the zigzag task.

flist = map (:[])
elist = flip replicate []
revNrev True = cycle [reverse,id]
revNrev _    = cycle [id,reverse]
transpN True = id
transpN _    = transpose 

zigzag m n = (transpN rev).map concat. transpose
 . uncurry ((.(map (liftM2 (++) (elist.(dl-).length) flist))).(++).(map (liftM2 (++) flist  (elist.(dl-).length))))
 $ splitAt k revcs
 where
  k  =  truncate . sqrt . fromIntegral $ (m*n)
  dl = min m n
  nd = abs (m-n)
  rev = m<n 
  pseudoAntiDiags = unfoldr (\((c:cs),xs) -> if null xs then Nothing else Just (take c xs,(cs,drop c xs)))
             ([1..dl]++(replicate nd dl)++[dl-1,dl-2..0],[0..m*n-1])
  revcs = zipWith id (revNrev rev) pseudoAntiDiags 

-- slower, almost complete emulation of the J-solution
groupon f x y= f x == f y
tab n = fst . until (null.snd) (\(xs,ys)-> (xs++[take n ys], drop n ys)) . (,) []
grade xs = map snd. sort $ zip xs [0..] 

zigzagJ m n = tab n. grade .concat $ zipWith id (cycle [reverse,id]) fdiag
  where fdiag = map (map snd). groupBy (groupon fst).sortBy (comparing fst)
                $ zip (map sum $ sequence [[0..m-1],[0..n-1]] ) [0..]
 
*Main> sum.map sum $ zigzag  500 500
1185103928
(0.69 secs, 103908376 bytes) 

*Main> sum.map sum $ zigzagJ 500 500
31249875000
(4.55 secs, 575802084 bytes)