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[[User:DanBron|DanBron]] 13:48, 2 September 2008 (UTC)
:: Hi Dan. I noticed your and TBH's activity on this wiki. Now you mention it, in time I'll think about a rabbit sequence task. Right now I'm working on Perfect Numbers (so far I have a generator based on the Lucas-lehmer test: not the tester that's asked for) and polynomial fitting (but that's in Haskell). --[[User:Gaaijz|Gaaijz]] 17:18, 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)
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