SpyrosAliv's blog

Codeforces Round 1020 (Div. 3)
By SpyrosAliv, 17 months ago, In English

Hello, Codeforces!

cry and I are very very very excited to invite you to participate in Codeforces Round 1020 (Div. 3), which will take place on Apr/24/2025 17:35 (Moscow time). You will be given 7 problems and 2 hours & 15 minutes to solve them. There will be at least one interactive problem, so please make sure to read this guide if you are not familiar with the format. One of the problems will be split into two subtasks.

The round will be hosted by rules of educational rounds (extended ICPC). Thus, all solutions will be judged on preliminary tests during the round, and after the round, there will be a 12-hour phase of open hacks. After the open hack phase, all accepted solutions will be rejudged on successful hacks. Also, note that there is no score distribution but the usual penalty of 10 minutes for each wrong submission, following the rules of educational rounds.

Remind yourself that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participant of the third division, you must:

  • take part in at least five rated rounds (and solve at least one problem in each of them)
  • not have a rating of 1900 or higher at any moment in time.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you (unless you register unrated).

Also, note the rule restricting the use of AI. If you are caught while breaking this rule, you will be terminated and haunted. So for your own safety, please do adhere to this rule.

This round would really not be possible without the help of the following people:

I hope to see you in the contest, and that you will be an honest and fair participant.

UPD: Editorial

UPD2: Winners!

All participants:

  1. Hamed_Ghaffari

  2. maspy

  3. TKT_YI

  4. BurnedChicken

  5. DevastatingStrike

Trusted & Rated participants:

  1. iren_eustia

  2. tarunnnnn

  3. alyzha

  4. nan1669

  5. CR7MEN7ALI7Y

  • Vote: I like it
  • +295
  • Vote: I do not like it

Comments Comments (97)
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17 months ago, hide # |
← Rev. 2  
Vote: I like it +25 Vote: I do not like it

As one of the non finite amount of testers, I wonder who all of the other testers are? I only see finitely many...

(how big is cry's basement?)

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17 months ago, hide # |
← Rev. 2  
Vote: I like it +3 Vote: I do not like it

As a tester, I like cows :)

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17 months ago, hide # |
← Rev. 2  
Vote: I like it +28 Vote: I do not like it

As a tester who proposed many rejected problems for the contest because they were known/boring/impossible , I can confirm that problem set is original and very interesting.

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17 months ago, hide # |
← Rev. 2  
Vote: I like it +17 Vote: I do not like it

As a tester and an initial contributor of great impossible unused problems, you might have noticed SpyrosAliv's haunting threat, and you better believe him...

Don't ask how I know (but I do)

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17 months ago, hide # |
 
Vote: I like it +8 Vote: I do not like it

As a participant, I can confirm SpyrosAliv loves tree problems

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17 months ago, hide # |
 
Vote: I like it +19 Vote: I do not like it

As a tester, I'm wondering how big cry's basement is?

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17 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

As a tester, SpyrosAliv's problems are quite delectable.

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17 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

Excited for another Div. 3! Thanks to all the authors and testers.

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17 months ago, hide # |
 
Vote: I like it +8 Vote: I do not like it

this time i dont want to cry after the round. Hope to reach pupil!

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17 months ago, hide # |
 
Vote: I like it +16 Vote: I do not like it

As a tester, I am the most useless tester known to mankind.

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17 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

As a tester.. ugh I'm running out of things to write in "As a tester" comments.

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17 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

Please marry me cry

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17 months ago, hide # |
 
Vote: I like it -9 Vote: I do not like it

Thanks Bombardino Crocodilo for bombing the homes of LLM cheaters and group solvers

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17 months ago, hide # |
 
Vote: I like it +8 Vote: I do not like it

As a tester, I confirm I am the one from cry's Basement

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16 months ago, hide # |
 
Vote: I like it +24 Vote: I do not like it

As a tester, there is a nonnegative number of problems that can be found on other judges in this contest.

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16 months ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

as a tester, i will find those who cheat.... and publicly shame them :)

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

As a participant I am disappointed that there is no mention of thanking the participants.

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16 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

Almost all the div. 3 in 2025 gives me -delta. But I choose to comeback and participate anyway... (help)

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16 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

As a participant, I hope not to get hacked in this contest.

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16 months ago, hide # |
 
Vote: I like it +5 Vote: I do not like it

I hope std::map does not give TLE in this round

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

orz! hope i reach newbie after this contest

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16 months ago, hide # |
 
Vote: I like it +12 Vote: I do not like it

As a tester, I can confirm I'll cosplay around March 80th.

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16 months ago, hide # |
 
Vote: I like it +13 Vote: I do not like it

As a participant, STOP CHEATING for fuck's sake

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I hope I will not reach pupil

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

What is the point of interactive problems?

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16 months ago, hide # |
 
Vote: I like it +5 Vote: I do not like it

Cry's competition： You can consider div4 as div3. You can consider div3 as div2.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

As a tester, -firefly- tested (again).

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16 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

A and B at least...

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I hope this will be my first contest to solve all of it within time, hope no 2300+ today :)

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16 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

As a participant, I hope to solve at least 5 problems

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

In last 2 div-3 rounds, my Handle changed from GREEN to CYAN. So, today I'm going to make this happen again tonight, inshaAllah...

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16 months ago, hide # |
← Rev. 2  
Vote: I like it +5 Vote: I do not like it

To cheaters :

Please don't use AI. Pls.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

As a participant, I hope I'll reach Expert

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I’m really excited for Codeforces Round 1020 (Div. 3), especially since the problem setters are experienced and well-known in the community. I’m sure the problems will be both challenging and fun to solve! Looking forward to participating and giving it my best shot

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

What does it take to AK this round ?

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

hmm this feels more doable than usually! good luck everyone!

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16 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

It was one of the best contests I've ever done, first time to be among top 100 (placed 94th) ^_^

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    16 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    how to solve D?

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      16 months ago, hide # ^ |
       
      Vote: I like it +1 Vote: I do not like it
      hint 1
      hint 2
      hint 3
      hint 4
      hint 5
      hint 6

      here is my solution for the problem (check the hints before look at it):

      solution
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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

[problem:E]This time, the questions seem much easier to understand and comprehend. However, there's an old saying: the simpler the question, the more complicated the matter. I feel like I'm stuck. Is there any expert who can explain E? I feel like a hungry wolf, eager to know the best solution for E. I have a hunch that there is one, but I just can't figure it out myself.

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    16 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    just simulate the binary search process, when the search is moving the l/r pointer to the wrong direction, you compulsorily move it to the right one, and count for these moments where you manually corrected the pointer. calculating the answer or determining if it's impossible would be trivial then.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

The solve rates alone indicate how well balanced this problemset was with respect to difficulty levels. Thanks for the gradual progression and many interesting problems! ^_^

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16 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

Stucked on D forever. Can someone explain it.

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    16 months ago, hide # ^ |
    ← Rev. 3  
    Vote: I like it +1 Vote: I do not like it

    go forward and backwards to find longest sub-seq that fits the problem.

    If sum of longest sub-sequence of both ends == k-1 then you minimize the answer along the way.

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16 months ago, hide # |
 
Vote: I like it +1 Vote: I do not like it

I bricked F, check out my spaghetti code mixed with bricks 317075083

Thanks for the good problem set, finally a good run div. 3.

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16 months ago, hide # |
← Rev. 2  
Vote: I like it +1 Vote: I do not like it

I misread E which made it buffed , i want to suggest it and its approach anyways.

basically consider the rearrangements to be allowed in only $$$l$$$ and $$$r$$$ rather than $$$1$$$ to $$$n$$$ that way you will have to use a segment tree to obtain the amount of elements greater and less than $$$x$$$ in the given range, and then use same logic.

Time complexity : $$$n *(log{n})^2$$$

Space complexity : $$$n *log{n}$$$

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

As a participant, I hope to reach cry's basement

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

the best div 3 in a while. Loved it!!

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16 months ago, hide # |
 
Vote: I like it +10 Vote: I do not like it

release editorial i need to upsolve it now cry

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16 months ago, hide # |
 
Vote: I like it +3 Vote: I do not like it

Nice Round!

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Nice problems. Yet again, my greatest pitfall, not reading the problem statements. I was sure problem G was about finding the root of the tree and not about finding the values haha. Although that does bring about an interesting question: how would one solve G2 if the problem was about finding the root of the tree? Like, in the case of G1, it's "pretty straightforward", but I couldn't figure out a clean idea for G2...

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

Thanks for problem F! It was a welcome change after the case-hungry problems before it.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

"Why is my contest Unrated? I participated fully but did not see any rating changes."

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    16 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    It's rated. But it takes time for rating changes. Right now there's a hacking phase that'll end after 9 hours. Then the full test cases will be run. Then the rating changes. By tomorrow it should take effect.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

could someone please explain why my rank is not the same in "common standings" and "friends standings" when not showing unofficial, but same when showing unofficial? Maybe the common standings exclude those who are't trusted participants while friends standings don't?

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    16 months ago, hide # ^ |
     
    Vote: I like it 0 Vote: I do not like it

    I have the same problem

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      16 months ago, hide # ^ |
       
      Vote: I like it 0 Vote: I do not like it

      it' even more weird that, I just check a previous div3 round and find that, the common standings, the frinds stanings, the rank on rating changes, and the rank on my profile are all different from each other. This is so weird.

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        16 months ago, hide # ^ |
        ← Rev. 2  
        Vote: I like it 0 Vote: I do not like it

        Common standings = trusted participant + unoffical (equals to all participant excluded non-trusted participants)

        Friend standings = all participant + friends filter

        Rating changes rank = all participant. But might get affected by plagiarism checker after contest. Rating changes rank should be equal to friends standings + not showing unofficial AFTER the rating rollback.

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I only solved three problems. hope i will not minus...

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Turing bless

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

I love these authors. Best Div 3 of my life! I tried D, E, and F they were crazy. I didn’t get to the others, but I’ll definitely try them soon!

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

I think sir cry was prevented from making cute silly statements this round. I kinda missed them tho

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

All codes were uploaded during live contest by the popular Codeforces Youtube Cheater — https://www.youtube.com/@Code-Review-c91/community

His channel has 1000+ subscribers and for each Codeforces Contest — his live solution leak videos have 2000-3000 views on average. Contests are cooked for all — because no one cares to report such people on Youtube.

I expected codeforces to atleast flag the codes which are mostly similar to the popular youtube code leaker channels which most people know.

When I check the standings every second person has similar codes as this Youtube Channel Cheater — all they have done is — tell AI to make small changes so their code looks little different LOL

@SpyrosAliv

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

THE PRETESTS FOR C WERE SO WEAK FOR TLE

i dropped from 5k to over 10k

i knew my soln to C wasn't the most efficient but i submitted it and it passed so i didn't think much

pretests took 300ms, limit was 2s

this is so unfair, if the pretests were stronger i could've fixed the soln in like 5mins

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16 months ago, hide # |
 
Vote: I like it 0 Vote: I do not like it

Hi I actually am not able to see any positive or negative rating change from this contest, although it was a rated participation. Is it possible some submissions are still under review and final rating for some participants has not been published yet, or have I been disqualified for some reason?

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