KAN's blog

By KAN, 4 weeks ago, translation, In English

Hello Codeforces.

Unfortunately a few hours after the end of Round #819 we were pointed out that one of the problems was stolen from another online judge.

Codeforces team strongly condemns such an action from the author. By no means is this acceptable behavior. This is the first and the most important rule of problem making: your problem should be new up to your best knowledge.

A lot of people put lots of effort into creation of every single round. You can find these people mentioned in the announcements and they indeed deserve these acknowledgments. And yet a single cowardly decision can ruin this huge work and experience of thousands of participants.

In this particular case the copied problem was not widely known, and it seems that this made little or no impact on the course of the round. Nevertheless, we stick to the decision that in such case the round cannot be considered successful, and thus no rating changes can be applied. We will also remove the problem from the round and from the problemset as well as blacklist the author.

We hope that this case will be a lesson for future authors and this situation does not repeat in the future.

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Can you share Which problem?

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4 weeks ago, # |
  Vote: I like it +262 Vote: I do not like it

Making the round unrated is unnecessary, IMO.

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    4 weeks ago, # ^ |
      Vote: I like it +82 Vote: I do not like it

    Agreed

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    4 weeks ago, # ^ |
    Rev. 4   Vote: I like it 0 Vote: I do not like it

    well, though I agree on this personally, there are still reasons to make this round unrated. I have seen many people suffer with F, both in the same room (room for hacks, not the physical room) and in the standings. Assume, in this situation, someone knew it was a stolen problem. In this case, they would have an unfair advantage! This unfair advantage is the exact reason to make this round unrated. While I am not a representative of Codeforces, I consider all such "unfair advantages" undesirable and therefore enough reason for making a round unrated.

    UPD: I understand both thoughts on either keeping the round rated or making the round unrated. However, as problemsetters, we (and by we I mean myself too, I prepare problems for other platforms) have many different values to pursue. These include fairness and justice. I hope you understand how this "unfair advantage" could be unjust and understand my idea as well.

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      4 weeks ago, # ^ |
        Vote: I like it +42 Vote: I do not like it

      Do you think a round should be unrated if one of the problems was similar to a existing problem because of actual coincidence?

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        4 weeks ago, # ^ |
          Vote: I like it +15 Vote: I do not like it

        This is quite hard to decide. But really, no, in this case we can attribute the advantage to the luck and wisdom of the ones who found a similarity. Some problems can be similar, it happens. When this happens, we can say that these people who found a similarity are very wise, being able to find a connection of the problem they're solving to one they did some time ago. That is a skill, after all. However for stolen problems, there is no "skill factor" over this. (If Googling is a skill, then maybe there is, but imho it's really not) When two problems are exactly the same, people can just copy-paste one side's solution to the other. There is then no more thinking about it, they just copy-pasted, got AC, that's it. While I personally think removing duplicates "entirely" is impossible (problemsetters are humans after all), they at least need to try their best to find out duplicates as much as possible in the problemsetting process.

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          4 weeks ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Ok, let me change the question. Do you think a round should be unrated if one of the problems was THE SAME AS a existing problem because of actual coincidence?

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            4 weeks ago, # ^ |
            Rev. 3   Vote: I like it 0 Vote: I do not like it

            Okay, if that's the case, then why not just make it unrated. We have some things to consider in this case though, such as 1. was it easy enough to find out the original problem? 2. did the coincidence give some participants an unfair advantage? 3. was the coincidence easily preventable? if 1 and 2 are true, then making it unrated should be a good decision. 3 though, is a hard question. there are tens of thousands of problems in the CP scene, if not millions. they should have tried their best in preventing coincidences, but as problemsetters are people, they can't review the massive amount of problems spread across different judges. if 3 is true, then the problemsetter may need a (weak) punishment, maybe a warning. but it's not an easy thing to simply say either 3 is true or not, after all detecting duplicates without the source problem in mind is hard.

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        4 weeks ago, # ^ |
        Rev. 5   Vote: I like it -13 Vote: I do not like it

        They even copied sample cases that can not be a actual coincidence.Codeforces has set of rules to be follow . That's what happened.I fully agree with the decision of KAN.

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    4 weeks ago, # ^ |
      Vote: I like it +14 Vote: I do not like it
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    4 weeks ago, # ^ |
      Vote: I like it -45 Vote: I do not like it

    Agreed strongly

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it -46 Vote: I do not like it

    What about those who touched new color first time and rolled back?? Genuinely feeling bad for them.

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    4 weeks ago, # ^ |
      Vote: I like it -14 Vote: I do not like it

    Agreed

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4 weeks ago, # |
  Vote: I like it -44 Vote: I do not like it

me after getting positive delta in the contest and getting rolled back:

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    4 weeks ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    +94 and the round is unrated, of course. It sucks, but ultimately I agree that there has to be a strong message sent out that plagiarism won't be tolerated for future problemsetters.

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4 weeks ago, # |
  Vote: I like it +149 Vote: I do not like it

Thanks for making this announcement. May I ask why you plan to remove the problem from the round/problemset when the same was not done for 1710E - Two Arrays?

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    4 weeks ago, # ^ |
      Vote: I like it +70 Vote: I do not like it

    Agreed: barring copyright concerns, it would be helpful to have the problem preserved so that e.g. the standings can be viewed as they were in the contest, the contest can be VCed, etc.

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      4 weeks ago, # ^ |
        Vote: I like it +73 Vote: I do not like it

      I also think that removing the problem from contest/problemset is unnecessary.

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        4 weeks ago, # ^ |
        Rev. 2   Vote: I like it +38 Vote: I do not like it

        The difference between this problem and other actual/notorious coincidences is that this time one of the dmoj staff wrote to coordinator Artyom123 expecting an appropriate action (against setters). Ig this is one of the reasons influencing the unavailability of this problem on codeforces.

        Spoiler
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          4 weeks ago, # ^ |
            Vote: I like it +18 Vote: I do not like it
          • Could you provide an evidence that such a request happened?
          • I don't think removing the problem from the round and problemset works as a punishment against the problem setter.
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            4 weeks ago, # ^ |
              Vote: I like it +15 Vote: I do not like it
            • Join the server (the link is present in spoilers in the previous comment), open the general channel and scroll up to read the last ~100/200 msgs. They were discussing contacting Artyom123, and later, one of them wrote that Artyom123 had read the message.
            • In the same server, you can also talk to their staff if you want to.
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              4 weeks ago, # ^ |
                Vote: I like it +10 Vote: I do not like it
              • I joined the sever and was able to verify that such a request did exist. Thank you very much.
              • DMOJ staff just said "they expect appropriate action", not "please remove the problem from the round and problemset". It is up to Artyom (and KAN?) to decide what action they will take, so I don't think the DMOJ staffs can provide an explanation.
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                4 weeks ago, # ^ |
                  Vote: I like it +21 Vote: I do not like it
                • It's just a grey area (I'm not a lawyer, and CF and DMOJ have their licenses wrt to problems); probably that's what Artyom (and KAN?) want to avoid, even tho they may have not asked for it.

                • I doubt at present Artyom (and KAN?) are going to revert back unless DMOJ staff explicitly says they don't have any problem wrt this problem being present on CF, after that people ask Artyom (and KAN?) again to add this problem back on CF.

                You can try going by this route if you care too much about this problem being available on CF.

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4 weeks ago, # |
  Vote: I like it +73 Vote: I do not like it

I do think this is a good decision, even if there was no impact, the behavior of the author should never be encouraged, and being unrated is also a warning to future authors.

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    4 weeks ago, # ^ |
      Vote: I like it +37 Vote: I do not like it

    Making the round unrated isn't important for the author who's copied the problem, Why should the rights of other authors and people who participated in the round be ruined?! Do you think it's fair?

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4 weeks ago, # |
  Vote: I like it +109 Vote: I do not like it

Nice. Next time when I drop ratings, I will connect my problem setter friend to make the round unrated.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

my friend got about +90 and he became a specialist for the first time and he was planning to pay for me in a restaurant, you spoiled it for me, that's not fair guys

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4 weeks ago, # |
  Vote: I like it +29 Vote: I do not like it

It's not the first problem that was copied for the contest. Neither it affected heavily the standings. What's so special about it to revert rating changes for everybody?

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    4 weeks ago, # ^ |
      Vote: I like it -26 Vote: I do not like it

    last time it was a Div.1 and a Div.2 separately, this time it's a Combined round. probably that is why the only options were to make it rated for all or make it unrated for all, in which the former would have been undesirable (last time's Div.1 was unrated too)

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      4 weeks ago, # ^ |
        Vote: I like it -9 Vote: I do not like it

      For those with low scores, they need to spend more energy and time to solve the first few easy problems in each game, but for them, the later problems have nothing to do with them , but they have something to do with them when they are leaked.Unrated is really fair?

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        4 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        unfair? okay, maybe. but did they have a choice? maybe not. It's a combined round, meaning that their only choice was to rate all or unrate all. the former is unfair to people who solved F and the latter is unfair to the ones who did not get to that point. do you think they really had a choice?

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          4 weeks ago, # ^ |
          Rev. 2   Vote: I like it -10 Vote: I do not like it

          In your opinion, how should we deal with this theft next time? Won't stealing stop just because of one or two warnings, or do we only choose the round that can do most of the questions? The number of participants in the 1+2 competition is even lower than that in some div.2 competitions.

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            4 weeks ago, # ^ |
              Vote: I like it 0 Vote: I do not like it

            If Codeforces had a way to recalculate the ratings with only the stolen problems excluded, that would be much better for the future.

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4 weeks ago, # |
Rev. 2   Vote: I like it +89 Vote: I do not like it

that's not fair we spent 135 minutes doing our best

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it -16 Vote: I do not like it

    I agree your point

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    yes yes, I totally agree with you

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    4 weeks ago, # ^ |
      Vote: I like it -9 Vote: I do not like it

    we made a great effort in this contest we want our money back

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      4 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      pardon me, you want whose money back?

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        4 weeks ago, # ^ |
          Vote: I like it -19 Vote: I do not like it

        it's an expression sentence meaning that we want our rates back. pay me some focus bro, my life is short:)

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          4 weeks ago, # ^ |
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          oh. I understand you fam, I lost rating due to this rollback too.

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      4 weeks ago, # ^ |
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      It's a shame we can't get our time back though.

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    4 weeks ago, # ^ |
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    yes bro and I don't like it at all that they have reverted the ratings just because of a single person's fault

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4 weeks ago, # |
  Vote: I like it +8 Vote: I do not like it

If you do it so you need to do the same for CF1710E bro.

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4 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

What a pity.

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4 weeks ago, # |
  Vote: I like it +41 Vote: I do not like it

I'm sorry, but I think this is unfair. We spent a lot of time solving these problems and the first 3 were good problems. I get that this should be a message to future authors, but you said that it made little to no impact on the round. I also got Pupil for the first time ever, and now this happens.. I don't know what to say, but I'm not happy about that

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

I wanted to participate in the contest, but skipped. When morning came, I heard the contest has become unrated? :/

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4 weeks ago, # |
  Vote: I like it +47 Vote: I do not like it

Please make it unrated next time when I drop rating, thx.

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4 weeks ago, # |
  Vote: I like it +17 Vote: I do not like it

Was not the first time.I think that codeforces should have some clear rules to curb such behavior.

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4 weeks ago, # |
  Vote: I like it +24 Vote: I do not like it

Making the round unrated is overkill in my opinion since so few people actually solved F. I hope this decision can be changed.

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    4 weeks ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    In ROUND810, div.2 also has the original question, and the result is still rated. This time there was unrated.

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4 weeks ago, # |
  Vote: I like it +18 Vote: I do not like it
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    4 weeks ago, # ^ |
      Vote: I like it +8 Vote: I do not like it

    Was there ever a conclusion reached that the problem was deliberately copied in that case? This seems to be the determining factor — coincidences can happen, but deliberate copying is forbidden.

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      4 weeks ago, # ^ |
        Vote: I like it -17 Vote: I do not like it

      How do you think about my ideas about why this round is unrated and the difference between coincidence and theft? There's a lot of downvotes, but I have no idea on the reason except for "toxicity". I feel like basically this community upvotes on every comment who sympathize with their own loss and downvote the rest. For all people who don't consider diversity of thought and think only for themselves, I have only one thing to tell you, shame on you!

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        4 weeks ago, # ^ |
          Vote: I like it +15 Vote: I do not like it

        I feel like basically this community upvotes on every comment who sympathize with their own loss and downvote the rest.

        Yea this is common, I remember when I wrote comments about FBHC they were initially upvoted, but then later became downvoted, possibly by people who want FBHC to move to the "code runs on server" format. Hard to know though.

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        4 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        I upvoted.

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      4 weeks ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      You can see 1591F is just like ARC115E. But the round is still rated, though more people found.

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        4 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        Was there ever a conclusion reached that the problem was deliberately copied in that case? This seems to be the determining factor — coincidences can happen, but deliberate copying is forbidden.

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          4 weeks ago, # ^ |
            Vote: I like it -23 Vote: I do not like it

          Okay, you guys make the rules. You have the right to explain.

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4 weeks ago, # |
  Vote: I like it +21 Vote: I do not like it

I spent a lot of time solving this round, but when I was happy that I was about to get promoted, you told me not to rate it. Although I can only solving A、B、C, it is obvious that not many people can solve F questions.

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4 weeks ago, # |
  Vote: I like it +32 Vote: I do not like it

I thought you were deleting the cheaters and i will get my rating back but this time the author is cheating

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

oh no

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4 weeks ago, # |
Rev. 3   Vote: I like it -13 Vote: I do not like it

Ok here's another idea. I went through the submissions and F was only solved by reds and a handful of Masters. So why not remove F from the contest and recalculate the scores, or just make it unrated for Div 1 like #810.

You are taking away a good contest from 95% of the participants who worked hard trying to solve A-B-C.

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4 weeks ago, # |
  Vote: I like it +19 Vote: I do not like it

me after getting bad delta

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4 weeks ago, # |
  Vote: I like it +10 Vote: I do not like it

I got +13 this time but I think this decision is perfectly valid. In order to make a completely fair decision from the perspective of the administrator, it is necessary to consider even participants who wasted time due to problem F and could not focus more on other problems. This is literally impossible.

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4 weeks ago, # |
  Vote: I like it +51 Vote: I do not like it

I participated in the contest with $$$102^{\circ}F$$$ fever, and now it has become unrated...

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    upvoted in wishes for your recovery. by recovery I mean both rating and health!

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4 weeks ago, # |
  Vote: I like it -10 Vote: I do not like it

please don't make the round unrated just remove the problem and its points plz :( :( :(

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4 weeks ago, # |
  Vote: I like it +6 Vote: I do not like it

Only a little participants solved the problem F,making the round unrated is unfair for other participants

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4 weeks ago, # |
  Vote: I like it +15 Vote: I do not like it

Current state of codeforces after this blog.
b14548a7fa9d82f4d34a586b91c4d315

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4 weeks ago, # |
  Vote: I like it +18 Vote: I do not like it

For those who are upset about the round being unrated, please appreciate the experience you had with all the other problems. The rating is just a number that simply estimates your ability, and having one or two unrated rounds wouldn't have much impact on its accuracy. But the real value for the contest is on the problem-solving experience, honing your skill and reasoning ability as you worked through a problem (even if it was the copied problem) and tried to implement a solution. None of this is being affected by having this round unrated.

While it's unfortunate that your efforts aren't reflected in your rating, this does not, in any way, erase the actual experience of the contest and its corresponding benefits.

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4 weeks ago, # |
  Vote: I like it +2 Vote: I do not like it

I just got Specialist last night,now back to Pupil

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4 weeks ago, # |
  Vote: I like it -19 Vote: I do not like it

Sometimes there are people who have done immense hard work in the contest. So you cannot turn a blind eye and make the contest unrated like it was nothing. At least the ones who didn't cheat should get their rights.

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4 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

Well I see the necessity in delivering a message to future authors in creating original problems. But when I saw myself being +126 on CF predictor and the round being unrated, I can't help myself being frustrated and well, pissed off

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4 weeks ago, # |
  Vote: I like it -17 Vote: I do not like it

Woke up to my +150 rating gone, actually gonna commit

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4 weeks ago, # |
  Vote: I like it -36 Vote: I do not like it

I know this may sound dumb but why not make the problem that was copied and every problem after that problem unrated. Say the contest has 7 problems and problem number 5 was copied then what if Codeforces just ignores problem number 5,6,7 and give the ratings on the basis of first 4 problems as if the problem number 5,6,7 doesn't exist. I know many will think why to make 6th problem and 7th problem unrated but you see some people will give more time and effort on the 5th problem than the people who knew that the problem was copied and they will quickly complete problem number 5 and move on to the next question which will give "unfair advantage" to those who knew the problem was copied. I know this solution is a bit stupid but it's still better than robbing the beginners who missed a very important Indian festival to give a Codeforces contest and solved A in 4 attempts B in 4 attempts got a positive delta of 47 had nothing to do with the copied problem but still the contest was unrated for him.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

As usual, I did well in the contest and now it's made unrated :((

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4 weeks ago, # |
  Vote: I like it -7 Vote: I do not like it

Dont make this contest unrated..

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4 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

If you make a round unrated only for one copied problem (Which didn't affect someone else's rank as mentioned in the blog), Then you should do it for another rounds too, You could make rounds 805 and 808 unrated too but you didn't, That's unfair, Also IMO making this round unrated wasn't necessary, Hope asap codeforces becomes real codeforces not googleforces.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

This is unfair. We spent 2 hours and 15 minutes to solve these problems. Now this round of contest has been unrated. This is not a punishment for the author but for the participants.

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4 weeks ago, # |
  Vote: I like it -17 Vote: I do not like it

Only a few people solved the problem!! Don't make the contest unrated rather punish the author of the problem.

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4 weeks ago, # |
  Vote: I like it -8 Vote: I do not like it

Woah got+101 in this contest and now it's unrated. Hard luck. I didn't quite get what's the point behind making it unrated.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Good decision for everyone. But thanks for other problems.

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4 weeks ago, # |
  Vote: I like it -8 Vote: I do not like it

So I get to reach my max rating with a 105+ in this contest and then wake up in the morning to see this? (sighs...)

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4 weeks ago, # |
  Vote: I like it +49 Vote: I do not like it

I support making it unrated, but why remove the problem? This would ruin the standings and make contestents lose their submissions.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I suggest removing problem E in last round but not this time because the impact on this problem is smaller, as the majority of contestants who passed this problem haven't seen this problem before.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Is there any punishment to the fake author themselves? in my opinion stealing a problem intentionally is worse than cheating

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4 weeks ago, # |
  Vote: I like it -11 Vote: I do not like it

This was my best performance in CF , solved 3 problems and got +223 rating and now it's unrated .....Bad luck ig.. Is it really necessary to make this round unrated ? Most contestants didn't even reached the problem statement of F.

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Imo this was way too unnecessary and disheartening.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Not very related to the above topic but I want to ask about problem A: What will happen to this statement if n = 1?

*max_element (a + 2, a + 1 + n);

Thank.

171076641 Wrong answer on test 23 *max_element (a + 2, a + 1 + n);

171158888 Accepted (n==1 ? 0 : *max_element(a+2, a+1+n) - a[1]);

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Because if n is 1 then that function goes range out(if I am not mistaken)

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4 weeks ago, # |
  Vote: I like it +16 Vote: I do not like it

Please make this round rated.

Making this round unrated would be a punishment for the participants.

Out of 10000+ participants just 50+ have solved that problem and also most of them were red or orange.

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    4 weeks ago, # ^ |
      Vote: I like it -9 Vote: I do not like it

    So orange or red participants are not participants? Only you guy the green participant is participant?

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      4 weeks ago, # ^ |
        Vote: I like it +2 Vote: I do not like it

      No

      I mean they are most probably authentic people which implies the problems were most probably not cheated.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Approx 50 people solved F. Making this round unrated is just unfair for almost everyone who participated in this contest. This actually seems to be a punishment for participants rather than author. Can't we just remove the problem F, this way it will have much lesser impact.

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

Wtf, that's not fair

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4 weeks ago, # |
  Vote: I like it +16 Vote: I do not like it

So disappointed. This round had great problems in my opinion. It's unfortunate that the hard work of the problem authors has been diminished.

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4 weeks ago, # |
  Vote: I like it +60 Vote: I do not like it

Rated div.1 contests are too rare nowadays, and on top of it, this happens.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    can you explain why they are rare ?

    are they running out of ideas for new problems or because the majority are in div2,3 so they don't focus on div1

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4 weeks ago, # |
Rev. 2   Vote: I like it +12 Vote: I do not like it

We will also remove the problem from the round and from the problemset as well as blacklist the author.

Could you explain why this has to be done as it seems like multiple people are against it? KAN

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    4 weeks ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    Pretty sure it is a violation of DMOJ terms of service by the author, assuming we include in material the intellectual property rights of those authors.

    You may not host material the DMOJ: Modern Online Judge owns on any website with online grading capabilities (without our consent).

    But that's not even the main issue I would say, do we really want to see the platform become a host of stolen problems, one where thieves get to rejoice at all the oblivious upsolvers years from now solving the problem while overlooking the fact it was copied? Deleting is the way to make it clear that any effort put into preparing stolen problems it will be wasted and thrown way once exposed, especially since legal recourse is pretty much infeasible.

    I suppose one could argue for a message in the statement exposing the event with a reference to the original source.

    In fact, I don't quite understand why the last copied problem has not been deleted as well along with this one. I feel like the same rationale should apply...

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      4 weeks ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      I suppose one could argue for a message in the statement exposing the event with a reference to the original source.

      I think this will be a good idea.

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      4 weeks ago, # ^ |
      Rev. 5   Vote: I like it 0 Vote: I do not like it

      The "Two Arrays" problem, as far as I recall, was copied from a source (Bytedance Grand Prix) which wasn't publicly available (or perhaps was but not in English) at the time of the contest (and it was also noted that a disproportionate number of in-contest solves were from people in China). I have been informed that there now currently exists a public online judge mirror here, but the user interface is all in Korean. (You can still kinda blunder your way through registration and submission by Google Translate and/or using the URLs as hints, but as a non-Korean-speaker I consider this a significantly less usable experience than DMOJ)

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4 weeks ago, # |
  Vote: I like it -38 Vote: I do not like it

KAN Sir as people are heartily requesting to make this contest rated, I would like to suggest you one thing. Remove this problem from the contest.. and just give ratings based on the other problems all of us have solved.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Stfu cheater

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    4 weeks ago, # ^ |
      Vote: I like it +39 Vote: I do not like it

    Calculating the score just based on the other problems does not work. During the contest, participants try their best to score as much as possible in the given set of problems. This often includes strategies like looking at the standings, skipping problems that seem difficult, etc. The removal of one problem can change participants' strategies significantly.

    I am good at data structure problems, so I often skip an adhoc-looking problem and try to solve a data structure problem. If after the contest it was decided that the data structure problem will be removed and ratings will be recalculated based on the score of other problems, I will feel that it is very unfair.

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      4 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      I'd like to know what you think will help solve this problem. After all, this competition has consumed too much energy.

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        4 weeks ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        I think just having the contest be unrated is fine.

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          4 weeks ago, # ^ |
            Vote: I like it +3 Vote: I do not like it

          What do you think if you count the people below 1900 who can't write F questions as div.2?

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            4 weeks ago, # ^ |
              Vote: I like it 0 Vote: I do not like it

            What do you mean by "can't write F questions as div.2"?

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              4 weeks ago, # ^ |
                Vote: I like it +3 Vote: I do not like it

              Sorry, there is something wrong with my expression. I mean, people with scores less than 1900 can't solve the F problem. So, can we say that most people with lower scores don't feel unfair? Then, can this group of people's achievements be regarded as a div.2 competition?

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4 weeks ago, # |
  Vote: I like it -44 Vote: I do not like it

KAN 50 or so people solved F, those too mostly reputable folks, so making the round unrated is harsh on the 10000+ people who actually sat for hours last night. Blacklist the author, mark the problem or anything else, but please dont make this unrated it is really really disheartening for all of us.

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    4 weeks ago, # ^ |
      Vote: I like it -24 Vote: I do not like it

    YES KAN please make round rated as problem F has not affected the contest that much.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Exactly. I got to Pupil for the first time ever this contest and now I'm back to grey. It's unfair to make the round unrated for 10000+ participants when only 50 of them solved the copied problem. Please consider returning rating changes for everyone KAN

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4 weeks ago, # |
Rev. 2   Vote: I like it -8 Vote: I do not like it

.

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4 weeks ago, # |
Rev. 2   Vote: I like it -14 Vote: I do not like it

It's ridiculous that the author didn't dare to go online, admit this behavior and apologise to the public. This is something that deserves our despise most.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

It has happened again.

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4 weeks ago, # |
Rev. 4   Vote: I like it -25 Vote: I do not like it

No, it's generally a strange situation, to be honest. If then (Codeforces Round #810 (Div. 1)) the Chinese contestants directly knew the solution and it was clearly visible that the stolen task had a strong influence on the results, then here is the task of 2017 from some super unpopular resource, where it was solved by one and a half people. In general, what are the probabilities that at least one of those who solved the problem then participated in this contest, and even remembers when and where exactly he solved it 5 years ago? I don't see anything wrong with making the task public. Apparently, the author thought the same and I agree with him. But the community, as usual, came up with a problem and unrated the contest for themselves, and now they are dissatisfied

Dont get me wrong. Its not about "i ve got positive delta — i am maaad now". Its all about undeserved hatred towards the author

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4 weeks ago, # |
  Vote: I like it +14 Vote: I do not like it

On both of my last 2 div1 rounds I had plus delta, and both of them were made unrated. In round 810 plagiarism had a strong impact, but this time the impact is NONE. I think you should not make this round unrated. And if you do, I think you should permanently unrate all of div1 rounds from this day.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    No I think it should. It will serve as a warning to future problemsetters.

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      4 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      The warning will not involve the time and energy cost of so many people. :)

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4 weeks ago, # |
  Vote: I like it +50 Vote: I do not like it

If this round is rated, it will be my first time to get Master. I can say I've been waiting for this day for five years. But the reality gave me a big blow.

Just for one problem, the contest is unrated. I think it's unfair for the 13,101 people who didn't solved this problem. And the most of us, even didn't reach that problem statement. This means that most people's efforts throughout the night are in vain. Additionally, I think the testers for this round also need to take some responsibility. This could have been avoided during testing, rather than announced it's unrated after the round. And throughout, the author little_angel didn't come out and give us an apology.

I cannot accept such a decision. I sincerely hope that this round will be rated again, KAN. Thank you.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Agreed. Maybe you should figure out some way of distributing the ratings but atleast don't be unfair with those who burnt their midnight oil to reach this point.

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    4 weeks ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    As I see it's unrated not because some people solved it, but because this has a bad effect on the image of Codeforces.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Well, negatively negative delta this time :D

Sorry for ones who now has negatively positive delta D:

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4 weeks ago, # |
  Vote: I like it +25 Vote: I do not like it

Lucky day for everyone with negative delta

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    4 weeks ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    I lost 70 points this round. I think im the most lucky contestant this round.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

I feel that I'm so lucky because I will drop 100+ rating if this contest is rated.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Amazing...

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Why aren't such problems rejected in first place when rounds are being prepared/coordinated?

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    4 weeks ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    Finding out if a problem is a copy is very difficult and you can't avoid it completely.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Just blacklist the authors and let the rating changes stay please. People worked hard on those problems and deserve some +ve delta

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4 weeks ago, # |
Rev. 2   Vote: I like it +4 Vote: I do not like it

Maybe there is an option for this kind of 'mixed' round situations?

Like, I'm not sure how possible this is, but my idea is to split it 'manually'. The last time this happened it was separated Div2-1 rounds. Later only Div1 was declared unrated since they weren't merged and the problem effect in Div2 was too brief.

Maybe in Div1+2 rounds you can split participants into 2 groups? Like it would have been for normal div2 and div1 rounds — Users with rating lower than 1900 remain rated and their scores are calculated separately from those with rating>=1900. For those with rating 1900 or more round can be declared unrated. I'm not sure how fair this is, but it probably is a lil 'fairer' than declaring round unrated for a problem F which was solved by 110 by now and probably even less on contest(not sure). Some people might have wasted time on it, but those most likely were 1900+ and they won't be affected either way.

Just an idea which might work, dunno.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    It seems that this idea should be reasonable, the number of people who score more than 1900 is not large, and it is almost impossible to write F with a score below 1900

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    4 weeks ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    I think the solution is to stop making combined rounds.

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      4 weeks ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Might be, but combined rounds are quite a good way to shift from div2 to div1.

      I have never been in this situation but I envision shifting from Candidate Master to Master to be hard, since the only div option you got is Div1, where the best of CF gather together. You can participate in Div1 from 1900 but well, not sure, I haven't been there yet.

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        4 weeks ago, # ^ |
          Vote: I like it +11 Vote: I do not like it

        As a CM you also get to participate in Div. 2 rounds if there is no Div. 1 round at the same time. Anyway I wouldn't worry about such things. Either you have the skills to reliably get to and stay in Master or you don't.

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          4 weeks ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Might be true, can't argue since I have never been there.

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4 weeks ago, # |
Rev. 2   Vote: I like it -14 Vote: I do not like it

g

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4 weeks ago, # |
Rev. 2   Vote: I like it -25 Vote: I do not like it

h

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4 weeks ago, # |
  Vote: I like it -10 Vote: I do not like it

This is unfair TT. For the thousands of people who are working their way up in competitive programming and don't even attempt F it's pretty harsh. Feels sad :(. Hope this doesn't happen again

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4 weeks ago, # |
Rev. 2   Vote: I like it -30 Vote: I do not like it

TOTALLY DISAGREE. this is unfair for the participants who just wasted two hours and more. there must be a compensation and appreciation for there time though it is not their problem.

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4 weeks ago, # |
  Vote: I like it -27 Vote: I do not like it

RATE THE CONTEST BBBBAAAAAAACKKKKKKKKKK!!!!!!!

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4 weeks ago, # |
  Vote: I like it +19 Vote: I do not like it

It's problem setter's fault, why unrated contestants?

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    totally agree

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I feel like this is a punishment to 10000 participants who did their best, just because a lazy author copied a problem only about 50 people solved during the contest. I got to enjoy being Pupil for the first time for a few hours I guess. But I'm disappointed enough to feel unmotivated about future contests.

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4 weeks ago, # |
Rev. 3   Vote: I like it +4 Vote: I do not like it

It's not fair. Please make the round rated again. Very few people only solved problem 'F'. Try to understand the situation of others who gave their best effort around 2 hour 15 minute.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

Out of curiosity, what would've been my rating change if everything was normal? I didn't check CF before rollback since I was just competing while working (so I assume it'd be rating loss) and last time I used rating predictor browser extension, it wasn't very accurate. Is there a reliable way to find out?

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    4 weeks ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    I use this sometimes, it's not very accurate, but gives you an idea. It usually displays a little lower gain than you would have actually got.

    F.E: the last time I used to check it, I got +137(in actuality, on CF) and the app displayed +(~110) or something similar.

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    4 weeks ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    I believe this is pretty accurate.

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    4 weeks ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    -63 by cf-predictor

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4 weeks ago, # |
  Vote: I like it +9 Vote: I do not like it

No need to make round Unrated

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

All the participants with positive delta getting punishment for author's fault. Not Fair!

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4 weeks ago, # |
  Vote: I like it +2 Vote: I do not like it

This had little to none impact on the contest, making it unrated is more punishing for those who worked hard to improve their ranking than for the one who committed the theft. It's unfair and i hope you will reconsider your decision.

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4 weeks ago, # |
Rev. 4   Vote: I like it -8 Vote: I do not like it

g

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4 weeks ago, # |
  Vote: I like it +24 Vote: I do not like it

kotatsugame was becoming LGM for the first time. I feel bad for what happened :( Hope you will reach LGM soon.

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    4 weeks ago, # ^ |
      Vote: I like it +66 Vote: I do not like it

    Thank you for mentioning! I will continue to participant in contests as much as possible and do my best.

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

I work for ten hours and then do cp just for rating. if I want skills, I can solve the problem on weekend. It's really a waste of time that the round become unrate. Doing cp then I only have 5 hours to sleep at night because of the work. It's totally no sense that someone said rating is not important.

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4 weeks ago, # |
Rev. 2   Vote: I like it +3 Vote: I do not like it
As a pupil
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4 weeks ago, # |
Rev. 2   Vote: I like it -12 Vote: I do not like it

This contest should be rated.

  1. Because every contest is slightly unfair.In each contest I find some solution publicly before the contest ended.

  2. If the problem setter made a mistake, then why contestant will suffer? Only about 100 people submitted the solution. I think most of them have solved it fairly.

  3. This will not be a lesson for future authors because few weeks ago same thing happened on CF and the sufferers are contestants.

I hope, if the same thing happen in future contest and then it would be rated.

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4 weeks ago, # |
  Vote: I like it +1 Vote: I do not like it

This way you punch us the author don't care about rating change ಥ⁠‿⁠ಥ

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4 weeks ago, # |
  Vote: I like it -16 Vote: I do not like it

It's not fair. Please make the round rated again. Very few people only solved problem 'F'. Try to understand the situation of others who gave their best effort around 2 hour 15 minute.

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4 weeks ago, # |
  Vote: I like it -9 Vote: I do not like it

unfair contest. dont know why you would even want to participate in this.
guys, if you care about your rating, i'd avoid this one.

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4 weeks ago, # |
Rev. 2   Vote: I like it +14 Vote: I do not like it

Why so many people care about their rating? You should solve CF contests for practice or/and for fun, not for rating.

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    4 weeks ago, # ^ |
      Vote: I like it +61 Vote: I do not like it

    says the guy who hasn't done a contest in 2 years to preserve his shiny yellow color.

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      4 weeks ago, # ^ |
      Rev. 2   Vote: I like it 0 Vote: I do not like it

      This is a coincidence :) I have left CP (atleast, solving, I'm still a problemsetter) right after May, 2020.

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    4 weeks ago, # ^ |
    Rev. 5   Vote: I like it +118 Vote: I do not like it

    For people in GMT+8, the contest runs from 1035pm to 1250am. Many people in east asian time zones have to purposely change their sleep schedules or endure 4 hours sleep to compete in contests. As others have pointed out, if you only care about practice, then virtual contests are same, if not better because I can compete at a better time.

    Personally, this is why I compete so rarely on CF because I have to wait for term breaks to purposely shift my sleep schedule to something closer to MSK so that my brain will work in the middle of the night.

    That said, although I am obviously unhappy about losing LGM, I support the decision to unrate the round.

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      4 weeks ago, # ^ |
        Vote: I like it +8 Vote: I do not like it

      Staying up all night really makes me tired, and the score is a part of my motivation.

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      4 weeks ago, # ^ |
        Vote: I like it +9 Vote: I do not like it

      Never thought about it, makes sense now. Thanks!

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I set a small goal of 1400 points. In more than two months, the change of scores gave me the motivation to move forward. Although I was only green, I didn't miss a game. I'm not afraid of losing points, but I'm afraid I can't see my own changes. Now after this competition, I fantasize about the improvement of scores and the possibility of reaching 1400 points tomorrow. unrate, where a small number of talents are affected, is unacceptable to me.

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    4 weeks ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    Rating is what gives me the most fun

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +16 Vote: I do not like it

    it seems you never wrote div2 round while being 2100+, contest is still not easy for you and should be fun on paper, but on practise it's not the same feeling as a rated round, there's much less fun when you know round is unrated for you.

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4 weeks ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

UnRated :(

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4 weeks ago, # |
  Vote: I like it +114 Vote: I do not like it

I thought I would just sit back and watch. However, I decide to write this comment.

If you drive a car too fast, it is illegal. It is not about whether your car crash into other people or not. It is about law, which states the speed limit.

In our community we do not allow authors to copy problems. It is not about whether this affects the round heavily or not. Therefore, the round should be unrated.

While I understand many people got upset for the round being unrated, I'd say I want to point out that about 4-5 years ago there was another point (not about copying problems): there are connection problems where people could not access the contest page for a significant amount of time. (FYI, later it is solved by introducing m1.codeforces.com, etc.) What happened? The round is declared unrated.

Making a round unrated is not an uncommon action. People should be prepared that some problems might happen during the contest. It is not about whether you tried hard for the round or not. There is a significant about of trouble and that's enough to make the round unrated. That's why I'm so tired seeing people arguing whether this round should be unrated or not. I just accept the decision written in this post and that's already OK.

What I want to discuss about is that how can we prevent such a problem (about problem theft) again in the future. I think there should be some better protocols (i.e., plagiarism check software, etc.) to prevent cases like this.

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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Out of self-interest, I want to restore the score, but the more important thing is to reduce future illegal operations.

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4 weeks ago, # |
  Vote: I like it +63 Vote: I do not like it

I have the feeling, many people misunderstand what a "rating" is. It is not some sort of highscore. You don't push it by solving more contests. You push it by learning and getting better. The rating is a measure about how strong of a CPler you are. As long as you participate in some contests your rating at some point will reach your skilllevel.

There are statistic fluctuations of course, and by solving more contests we expose ourselves more to them and can probably get a higher high-score-rating, but in general that is not what a rating wants to measure.

Be happy you participated in this contest and had fun with great tasks! I for one learned much from Problem E and I had much fun with C and D.

I'm genuinely sorry for the people who only seldom find time for contests though and had to make time. Better luck next time!

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

You can ban the ip of the contest checker,but you should not punish all coders.

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4 weeks ago, # |
  Vote: I like it 0 Vote: I do not like it

I think cf should make ken newbie again

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4 weeks ago, # |
  Vote: I like it +3 Vote: I do not like it

But that was +99 for me :')

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4 weeks ago, # |
  Vote: I like it +7 Vote: I do not like it

Good thing you guys are gonna blacklist the author. A strong message needs to be sent out that such activities will not be tolerated. I saw the author put out an apology blog yesterday but has now deleted it. Guess he doesn't feel sorry for his deed after all.

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4 weeks ago, # |
Rev. 2   Vote: I like it +41 Vote: I do not like it

I noticed that further submissions to CFR819-F are not accepted now. here
I hope completely remove the problem (and keep the statement, ranklist... somewhere else if it's needed) rather than keep the problem slot, so that innocent future upsolvers can get the green lamp (all upsolved).

P.S. How about CFR810-D1E?

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4 weeks ago, # |
  Vote: I like it -14 Vote: I do not like it

Since I would have lost a lot of rating (due to FST), I strongly agree with this decision! :)