Disclaimer: this post contains my thoughts and suggestions. Feel free to discuss the topics in the comments

[TL;DR] Cool problems, issues, why not semi-rated.

First of all, I'd like to congratulate Um_nik for making the simultanously best and worst round I've seen in a while :) On a more serious note, I've really enjoyed solving your problems, in contrary to some yet-another-segment-tree-problems. Especially B was quite unusual when it comes to CF.

However, there are some issues brought up by geniucos here which I completely agree with. Memory limit issues are really rare, and you usually realize that when you get MLE1 after submitting. Unfortunately, it was not possible today, so some participants were affected quite much (hello Swistakk.

Moreover, it wasn't only a case of MLE. "Incorrectly" solved problem B required using random generators. And now the standard CF feature — RAND_MAX is 32767. I've tested my solution locally and was quite shocked to see WA10 after the long queue ended. Looking at my submission: oh, RAND_MAX. Let's fix it. Wait. The round has ended 3 hours ago =) Of course you can say this should fail. But the problem is that such solutions passed. Look at 38734837 or 38747568. Especially no tests with N = 1000 and answer Um_nik — seem quite weak.

And well... the queue. 30 mins is in no circumstances a "very end of the contest". Even in an OI-style contest it's quite a lot of time. Of course, participants who didn't submit anything during this time were not affected at all. Usually submits during this time belong to most important problems — or at least the hardest we could solve. So it is imho the most important period of time. Some participants passed systests without any problems, some got FST and some got errors on pretest1. My C submission fortunately passed pretests with 3950ms (with TL = 4 seconds). Of course, everyone would realize his implementation is not efficient enough after getting such verdict.

Now, the most important part. There were some other options used in the past other than binary rated. If semi-rated didn't sound like a good idea, then maybe you could at least allow participants who were severly affected by the long queue to be excluded from the official ranklist, just like cheaters are (but no bans please)? I'd be very grateful an for official response. Attention tag. KAN.

My apologies for everyone who had to read this boring wall of text. Cheers :D