||I'm from the team that ranked first in the regionals. I expected this suspicion will come out, but rest assured, after you read the problem set, I hope you will not wonder anymore, the problem set is really "easy".
Many of the problems are straight-forward - you just have to know how to solve it - and then almost any implementation will work. I myself at one point wondered why the other teams are taking its time. I'm not sure yet - perhaps they only have one implementor, or perhaps their technique is different. Perhaps, one of the reasons, too, is because we're used to relatively easy problems. For example, many of our practice problem sets are from GNY (which are relatively easy compared to others).
We solved Problem D fast because it's really straightforward and the only "difficult" part is input parsing and output format, and we're used to that. We clarified the wrong output example in Problem D, and the judges even said that it is really correct. But we are confident in our solution so we submitted anyway. This is not the first time an example output is wrong in the problem set (especially contests held here in the Philippines), so we just submitted it and hope that if it's wrong, we can clarify later better. Fortunately, it's correct.