I'm not sure how to approach these two problems:

http://main.edu.pl/en/archive/oi/2/obc

http://main.edu.pl/en/archive/oi/14/wag

The first one seems like some dfs, and I really have no clue about the second one (maybe dp?).

Any ideas or hints? Thanks!

Could someone give me a hint for this problem?

http://main.edu.pl/en/archive/oi/2/jez