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.
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.
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.
Thanks Again!
On Fri, May 14, 2010 at 8:42 PM, Daniel Fischer
On Saturday 15 May 2010 03:13:24, Diego Echeverri wrote:
Hi guys.
I've been playing with https://www.spoj.pl/ to get better with Haskell. I'm trying to do: https://www.spoj.pl/problems/PALIN/
Basically given a number k, you have to find a number bigger than k that is palindrome. The thing is that k can be 1000000 digits long.
I have learnt a bunch of things doing this exercise but I'm still getting time-limit exception.
Here's the code: http://gist.github.com/401880
I believe that the bottleneck is in the addOne function (Specially in the case where you have a bunch of nines). I have rewritten it to use STArray but isn't fast enough. doing: addOne $ B.replicate 500000 'a' takes too much time!
Can anybody point me out of better (faster) ways to improve the code? I don't need my code fixed, just suggestions and clues about things to try.
Thanks! Diego Echeverri
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.
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.
Third point: Use STUArrays and not STArrays if possible (much faster).
-- Att: Diego Echeverri Saldarriaga