What are some of the best problemsets in competitive programming contests? (ICPC or IOI practice)
My views: I find USACO Contest problemsets very intersting. Reason: Short and interesting problem statements, nice editorial with nice readable codes.
Which problemset do you find most interesting/challenging?
Andrew Stankevich Contests http://mirror.codeforces.com/blog/entry/7770
Where can I find editorials and codes of these contests?
Contests by Sereja http://mirror.codeforces.com/contests/writer/Sereja
Only these: http://mirror.codeforces.com/blog/entry/44305
Codeforces Round #192. Enjoyed this round a lot. Most of the problems in this round has unexpectedly simple solution (like Div2-B, Div1-B, Div1-C, Div1-E), and Div1-D is a fun puzzle.