Is there a way for me to run old challenge problems?
Yeah, you can find them in challenge section.In general for example the problem code is let us say ‘FACTORIZ’, then you can open the problem by http://codechef.com/problems/FACTORIZ
Yeah. All challenge problems are shifted to this link after the contest: http://www.codechef.com/problems/challenge
You can practice here.
I can only see the problem statement , but not solve it ?