[Haskell-beginners] Help with slow algorithm

[Daniel Fischer]

On Saturday 15 May 2010 04:00:06, Diego Echeverri wrote:
> Hi Daniel. Thanks for your answer.
>
> > One point: Packing a long list is bad. That takes a lot of memory and
> > is slow, if you create a list, it's going to be faster to use normal
> > String-IO to output it.
>
> The thing is that later I do some operations with it (solve). just by
> changing to ByteString everything got faster.
>

You should think a little about avoiding that.

> > Another point: biggerOrEquals is also too slow. Using the Ord instance
> > for ByteStrings will be faster. But I think splitting the ByteStrings
> > isn't the best way.
>
> The Ord instance of ByteStrings is lexicographic. This way:
>
> B.pack "1111"  > B.pack "112" ==> False
>
> Although given the fact that both strings would be the same length,
> the Ord instance may work just fine.
>

Quite. You only test ByteStrings of equal length, so the Ord instance works 
fine.

> > Third point: Use STUArrays and not STArrays if possible (much faster).
>
> Not sure if those are available in the Online Judge. I'll try it.

They're also provided by Data.Array.ST, so they are available.

>
> Thanks Again!
>
>