[Haskell-cafe] Optimization problem

Magnus Jonsson magnus at smartelectronix.com
Thu Sep 14 09:06:11 EDT 2006

On Thu, 14 Sep 2006, Ketil Malde wrote:

> Magnus Jonsson <magnus at smartelectronix.com> writes:
>> splitStreams::Ord a=>[(a,b)]->[(a,[b])]
>>> splitStreams [(3,x),(1,y),(3,z),(2,w)]
>> [(3,[x,z]),(1,[y]),(2,[w])]
>  [...]
>> But is there any way to write it such that each element is touched
>> only once? Or at least an O(n*log(m)) algorithm?
> I guess it should be possible to use a quicksort-like algorithm,
> splitting the stream into three streams with keys less than, equal,
> and greater than the first element, and recurse on the less/equal
> streams?
> -k

That is probably the best we can do. I think in a hypothetical concurrent 
Haskell with futures/promises, the split stream problem could be solved. 
But if it can be solved in regular Haskell, I would be pleasantly 

/ Magnus

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