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).