[Haskell-cafe] Code Golf
Emil Axelsson
emax at chalmers.se
Wed Apr 15 07:07:39 EDT 2009
Why not:
diag = [(x, sum-x) | sum <- [2..], x <- [1 .. sum-1]]
/ Emil
MigMit skrev:
> If I understand the problem correctly...
>
> Prelude> let diag = concat . diags where diags ((x:xs):xss) = [x] :
> zipWith (:) xs (diags xss)
> Prelude> take 10 $ diag [[ (m,n) | n <- [1..]] | m <- [1..]]
> [(1,1),(1,2),(2,1),(1,3),(2,2),(3,1),(1,4),(2,3),(3,2),(4,1)]
>
> Sebastian Fischer wrote on 15.04.2009 14:32:
>> Fancy some Codegolf?
>>
>> I wrote the following function for list diagonalization:
>>
>> > diag l = foldr (.) id ((sel l . flip sel) ((:[]).(:))) []
>> > where
>> > sel = foldr (\a b c -> id : mrg (a c) (b c)) (const []) . map
>> (flip id)
>> >
>> > mrg [] ys = ys
>> > mrg xs [] = xs
>> > mrg (x:xs) (y:ys) = (x.y) : mrg xs ys
>>
>> Self explanatory, isn't it? Here is a test case:
>>
>> *Main> take 10 $ diag [[ (m,n) | n <- [1..]] | m <- [1..]]
>> [(1,1),(1,2),(2,1),(1,3),(2,2),(3,1),(1,4),(2,3),(3,2),(4,1)]
>>
>> I was trying to golf it down [^1] but my brain explodes. If you
>> succeed in reducing keystrokes, I'd be happy to know!
>>
>> Cheers,
>> Sebastian
>>
>> [^1]: http://codegolf.com/
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