On Saturday 15 May 2010 10:29:12, Heinrich Apfelmus wrote:
Diego Echeverri wrote:
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!
Are you sure that you are using a fast algorithm? For instance, starting with k and counting up until you reach a palindrome is definitely not a good idea; you need to do something cleverer.
Deceived by a name :) He did something cleverer. His algorithm is good, just the implementation leaves much room for improvement.
Regards, Heinrich Apfelmus