### TheScrasse's blog

By TheScrasse, history, 12 months ago,

## UPD: I was wrong :(

#### UPD2: I was wrong, again.

Hello everyone,
I see that many people complain about copied problems. Their claim is that authors weren't able to come up with some problems, and decided to copy them from other sources instead.

Comments of last round

Although a contest shouldn't have already used problems, please convince yourself that no problemsetter would copy problems deliberately. The presence of some problems from the Internet is accidental. So, it's not correct to accuse the authors to "copy" the problems.

FAQ:

Q. The statement is completely the same, isn't it obvious that the problem was copied?
A. No. Proof: I invented 844C - Sorting by Subsequences and 1088D - Ehab and another another xor problem, with the same statement. Usually, if you want to write the statement formally, there is only one way that's much more convenient to use that the others.

Q. Maybe you remembered the statement because you had already read it without solving the problem?
A. No. Proof: I invented 1501C - Going Home and arc130_d before the contest.

Q. How is it possible that no author / tester was able to find the "copied" problem by googling?
A. Challenge: find arc115_e on Google, using only the statement of 1591F - Non-equal Neighbours.

• +255

 » 12 months ago, # |   +111 years ago I believed that the solution to find problem by statement is NEAR
 » 12 months ago, # | ← Rev. 2 →   -140 3 copied problems in one contest? Really is it a coincidence?
•  » » 12 months ago, # ^ |   +48 I think it would be more apt to call them 'pre-existing' problems rather than 'copied' problems for the simple reason that they weren't copied. While it sucks that these problems had coincidentally been invented by someone else at an earlier point in time, saying that they are copied is basically shitting on all the authors' efforts and the whole problemsetting process really. Rude.
•  » » » 12 months ago, # ^ |   -12 How can you be so sure that it was just a coincidence that all the three problems were already on some other coding platforms?
•  » » » » 12 months ago, # ^ | ← Rev. 3 →   +14 How many problems have you done? As you are on an alt, i'll bet at most 100. I've done nearly 2k on codeforces, and over 1k among other judges, yet I still hadn't seen any of those particular problems that you listed as the same as yesterday's problems (I might've seen a similar one to F on cf before, but also can't remember source). No matter how many problems you do across any number of judges, it's impossible to know every problem that has existed in some previous contest.
•  » » » » » 12 months ago, # ^ |   0 THe alt did 11 total problems :P
•  » » » » » 12 months ago, # ^ |   +11 At least in my case, C was an already solved problem. I have not solved D or F earlier. During the contest, I could solve only the first 4. My friends were super quick in solving F, and as a result, I wasted time on solving F instead of doing E first. These things hurt, that the solution is already posted publicly. Whether it was copied or it was merely a coincidence that 3 problems were found on other judges, in any case, the contest was poorly managed. About the number of problems solved, it doesn't matter really.
•  » » 12 months ago, # ^ |   +11 Have you ever tried problem-setting?
•  » » » 12 months ago, # ^ |   -64 No, but I could have set the div1 round, simply copy the testcases and problems from code jam finals, hackercup and atcoder grand contests. If the two solutions can be penalised, if they are exactly same or similar, then why problem setters or testers cannot not be penalised, if the problems are exactly same. Penalty could be — banned as a setter for next 1 yr or more or something else.
•  » » 12 months ago, # ^ |   +8 Chill bruh ,have my downvote
•  » » » 12 months ago, # ^ |   -46 Thanks a lot, for commenting such a wonderful, knowledgeable stuff.
 » 12 months ago, # | ← Rev. 2 →   +8 I really appreciate the efforts of the authors.
 » 12 months ago, # |   +45 Too bad this doesn't exist
 » 12 months ago, # |   -9 I don't care if they were copied or not.Overall the problems were great and we shouldn't accuse the testers and authors to conduct contests. I hope they will learn from the mistakes and bring a really good contest next time
 » 12 months ago, # |   +53 Anectodal: I once prepared a problem for local studies with my high school students. 13 days later, I encountered the exact same problem as participant. That helped :) . Needless to say, neither me nor the other problem author knew about the other problem being prepared.
 » 12 months ago, # |   +54 I totally agree with you, but just please don't commit crimes on mathematics by doing proofs by exaples...
 » 12 months ago, # |   +29 I agree with the opinion that "No problemsetter would copy problems" however I think that there should be a special tester (probably more than one) that has a good knowledge of the problems that were used in the past contests. Definitely, this will not solve this issue completely but I hope that it will make it less probable to happen.
•  » » 12 months ago, # ^ |   -7 Ez. Just have all LGM as testers
•  » » 12 months ago, # ^ | ← Rev. 3 →   +9 It is not that simple. For some reason, technocup rounds only start testing literally a few days before the contest (usually cf contests do testing way before the round is released in case of stuff like this). If someone says that a problem is copied it is basically impossible for them to make a new problem. Consider 1608E - The Cells on the Paper from the recent combined round I tested. The entire idea for this problem is literally in Singapore's IOI trainings (update: found the task). But the coordinator has no choice because he literally didnt have anything to replace it with.The only way to solve this is if we just stop having rated technocup mirrors on codeforces when they are super rushed in preparation. Furthermore, the task types are usually not suited for CF (such as Codeforces Round #755 (Div. 1, based on Technocup 2022 Elimination Round 2) where C-E were all idealess implementation), not to say that technocup rounds are always bad, Codeforces Round #749 (Div. 1 + Div. 2, based on Technocup 2022 Elimination Round 1) was a amazing contest, but technocup rounds usually like this.
 » 12 months ago, # |   +35 Well, some problemsetters do (cf. notorious coincidence meme)
 » 12 months ago, # | ← Rev. 2 →   0 The fact that there is still no tutorial for this problem, makes me doubt that enough time was spend preparing it.
 » 12 months ago, # |   -24 Even modulo value also copied :|
•  » » 12 months ago, # ^ |   +30 $998244353$ is the most used modulo.
•  » » 12 months ago, # ^ |   +18 Obviously they copied it from my name /s
 » 12 months ago, # |   +21 Another anecdote: I was a problem setter on HackerEarth once and one of my problems appeared on Codeforces ONE day before the HackerEarth contest.Worst part is, I only noticed it late and didn't even AC it for free rating since my problem had lower limits to avoid overflow issues :(
 » 5 months ago, # |   +188 Auto comment: topic has been updated by TheScrasse (previous revision, new revision, compare).
 » 5 months ago, # |   -15 hi . div 2 E — div 1 C is copy too!this is link of the solution https://blog.csdn.net/qq_35577488/article/details/117813076
 » 3 months ago, # |   +2 Time to get the blog back to the recent actions XD
•  » » 3 months ago, # ^ |   +20 the moment when UPD 2: I was wrong twice D:
•  » » » 3 months ago, # ^ |   -13
 » 3 months ago, # |   +26 Auto comment: topic has been updated by TheScrasse (previous revision, new revision, compare).
•  » » 3 months ago, # ^ |   -17 TheScrasse I think you should add links to the disrespective contest announcements in the texts of upds
 » 3 months ago, # |   0 No one from coding club of IIT KGP would try setting problems for CF contests for a long time now lol