In today's TopCoder SRM 816, the hard problem was a textbook flow problem (which was given previously as "Hard Life" on NEERC 2006 and probably in other places).
Out of 9 accepted solutions:
According to TopCoder rules, this is not allowed (see "Using pre-written code" here).
Normally, this rule is not a big deal. However, in case of a textbook problem like this one, using code that can be found on the Internet gives a huge advantage. I knew that it's a well-known problem, but I did not copy-paste old code from somebody else because it is against the rules. Other people did, and got higher score, which is unfair.
I'm not a fan of this rule, and I'd prefer copy-pasting code from others was allowed as it is on almost all other platforms, but in the current state it leads to a disadvantage for me because I follow the rule and some others don't.