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physics0523's blog

By physics0523, history, 9 days ago, In English,

Codeforcesの皆さん、こんにちは!(Hello, Codeforces!)

I'm glad to invite you to my first contest, Codeforces Round #654 (Div. 2) which will be held on Jul/01/2020 16:35 (Moscow time) (notice earlier time than usual). All of the problems were mainly written and prepared by me. The round is rated if your rating is strictly less than 2100.

You will be given 6 problems (one problem has a subtask) and 2 hours to solve them. Please, read all the problems.

I would really like to thank:

The scoring distribution will be announced later.

Good luck, have fun and wish your high ratings :)

UPD: Scoring distribution : $$$500 - 1000 - 1250 - 1500 - (1500 + 1250) - 3000$$$

UPD: Editorial is out

 
 
 
 
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9 days ago, # |
  Vote: I like it +2 Vote: I do not like it

Auto comment: topic has been updated by physics0523 (previous revision, new revision, compare).

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9 days ago, # |
  Vote: I like it +28 Vote: I do not like it

Thanks for all of these frequent rounds!

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9 days ago, # |
  Vote: I like it +137 Vote: I do not like it

I hate Physics. Hopefully no problem related to physics!

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    9 days ago, # ^ |
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    Oh god, you read me! I'm afraid of this.

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    8 days ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    Even though I love Physics , I still hope there will be no physics related problems. XD.

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    7 days ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    same here pal.XD

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    7 days ago, # ^ |
      Vote: I like it +19 Vote: I do not like it

    I think Physics problems would be easier than the problems in this round

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9 days ago, # |
  Vote: I like it +6 Vote: I do not like it

Good luck on your maiden round!

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9 days ago, # |
  Vote: I like it +61 Vote: I do not like it

As a tester, I can say that the problems are really interesting and hopefully you will enjoy solving them :)

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    9 days ago, # ^ |
      Vote: I like it -273 Vote: I do not like it

    I dont know why testers are commenting a lot just for upvotes!? The only thing you done is you participated in a contest few days before most of the people and i dont see anything special to upvote u!

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      9 days ago, # ^ |
        Vote: I like it +569 Vote: I do not like it

      The only thing you done is you participated in a contest few days before most of the people and i dont see anything special to upvote

      Nah this isn't the only special thing about testers.
      He also left one rated contest so that others can enjoy one round.

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      9 days ago, # ^ |
      Rev. 3   Vote: I like it +251 Vote: I do not like it

      Down voted, it's not true about many testers, you can't even understand how hard being a good tester is.

      P.S. I feel personally attacked. =(

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        9 days ago, # ^ |
          Vote: I like it -285 Vote: I do not like it

        Oh my god! Ok i upvoted you becuase its the only thing you want :( and its you third time you are editing your comment to dont get downvote!

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          9 days ago, # ^ |
          Rev. 2   Vote: I like it +240 Vote: I do not like it

          What is wrong with you, I want you to understand how important testers are, some of testers duties are :

          1. They should try submitting heuristics/wrong solutions, to make sure tests are strong enough.

          2. They should help problem setters to replace the problems if needed.

          3. They should write many different solutions for a single problem(if needed), to make sure unintended solutions that are wrong or are slow wont pass.

          4. Doing many other things to make sure tests are strong, problems are not spoiled, statements are clear, pretests are fine and etc.

          I saw that your comment has many upvotes, so it probably means many people don't know about testers, so I wrote this to show you how being a good tester is , not for upvotes.

          P.S. I enjoy editing my comments, you cant blame me for that.

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            9 days ago, # ^ |
              Vote: I like it -259 Vote: I do not like it

            Upvoted as i said

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            8 days ago, # ^ |
            Rev. 2   Vote: I like it +45 Vote: I do not like it

            Agreed. A good contest is the result of hardwork and collaboration of all testers, problem setters and coordinators.

            I would like to thank all of you for making so many good contests for us.

            Hope to have fun in this contest too:)

            All the best to all!

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      8 days ago, # ^ |
        Vote: I like it +229 Vote: I do not like it

      As a tester, I can confirm that we do absolutely nothing in a grand conspiracy to gain contribution points by making meaningless confirmations on the contest announcement.

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    8 days ago, # ^ |
      Vote: I like it +33 Vote: I do not like it

    this is what all testers say about their rounds:))

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      8 days ago, # ^ |
      Rev. 2   Vote: I like it +10 Vote: I do not like it

      Wait for the next Global round. :)
      For spoilers about tester comments of next Global join AC.

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    7 days ago, # ^ |
      Vote: I like it +107 Vote: I do not like it

    Scam

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    7 days ago, # ^ |
      Vote: I like it +50 Vote: I do not like it

    Proof of a conspiracy theory by testers to gain contribution.

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    7 days ago, # ^ |
      Vote: I like it +48 Vote: I do not like it

    Frequent comments like these is why nobody takes such comments seriously now!

    If you found the questions interesting, you are clearly lying and spamming for contribution. As simple as that.

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      7 days ago, # ^ |
        Vote: I like it +30 Vote: I do not like it

      Or maybe they simply should be banned of the tester position as they have a much different taste for problems than the CodeForces community does.

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    7 days ago, # ^ |
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    Did some comments disappear? I think I saw few other replies to this comment yesterday.

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Yes, lewser's reply disappeared, and all of the replies to it with it.

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

        Do you think this is intentional or some other bug in the Codeforces website?

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          7 days ago, # ^ |
            Vote: I like it +6 Vote: I do not like it

          Probably intentional.

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          7 days ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Yes,It's intentional..After many negative vote some commment filter out.I think this feature added from past 2 contest ..I think it's a good initiative.

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      7 days ago, # ^ |
        Vote: I like it +16 Vote: I do not like it

      Yes. They tried to silence me revealing the secrets about the tester-contribution conspiracy.

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        7 days ago, # ^ |
        Rev. 2   Vote: I like it +9 Vote: I do not like it

        Hi i forgot to reply your message when my comments was there. you replied me that you and lots of testers didnt do it! And im gonna say yes! I agree and i was saying some of them are doing it in every single contest and i was replied to tester i think that its not fair! I dont realy care about upvotes and downvites i just say something that i believe so im sory if any one get mad at me becuase if those comments but im saying that these kind of works are not cool :(

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          7 days ago, # ^ |
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          some of them are doing it in every single contest

          I agree with that, but I'm not one of them, I joke about those things sometimes, but I really don't mind.

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    7 days ago, # ^ |
      Vote: I like it +58 Vote: I do not like it

    Codeforces should have option of downvoting comment even after upvoting it.

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      7 days ago, # ^ |
        Vote: I like it -14 Vote: I do not like it

      You can still downvote the comment next to that one.

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9 days ago, # |
  Vote: I like it +209 Vote: I do not like it

I was master when I tested the round, I wouldn't have done it if I knew I would have missed such a great round :((

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9 days ago, # |
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What is the meaning of subtask? Does this mean a problem will have an easy and a hard version?

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9 days ago, # |
  Vote: I like it +64 Vote: I do not like it

Glad not seeing comment section filled with memes this time

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    9 days ago, # ^ |
      Vote: I like it -21 Vote: I do not like it

    May be someone is still trying to make new memes! :)

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9 days ago, # |
Rev. 5   Vote: I like it -57 Vote: I do not like it

Good luck everyone. This community is insane lol

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    8 days ago, # ^ |
      Vote: I like it +22 Vote: I do not like it

    Here I was wondering why there were so many negative feedbacks until I saw the revision history XD

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

      I just said I loved physics and people got offended, so had to change. I still don't know the reason

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        7 days ago, # ^ |
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        Nobody's got offended, and nobody cares whether you love physics or hate it.

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        7 days ago, # ^ |
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        Its not necessarily that people are offended. They might not agree with your opinion and hence the negative feedback.

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9 days ago, # |
  Vote: I like it +46 Vote: I do not like it

頑張って皆!Good luck everyone!

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9 days ago, # |
  Vote: I like it +28 Vote: I do not like it

I love Japan and the Japanese so i'm excited for contest :D

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9 days ago, # |
  Vote: I like it 0 Vote: I do not like it

(one problem has a subtask) this seems in-ter-uh-sting

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8 days ago, # |
  Vote: I like it -42 Vote: I do not like it

Hope , we will see Geometry related problem.

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8 days ago, # |
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Looking forward to this round!

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8 days ago, # |
  Vote: I like it +16 Vote: I do not like it

Physics is evrywhere :v

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8 days ago, # |
  Vote: I like it +3 Vote: I do not like it

My UI of codeforces has been shifted to left side and I'm unable to see users and search problems with specific rating, Is there anyone facing the same issue since morning?

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8 days ago, # |
  Vote: I like it -75 Vote: I do not like it

well all the testers can anyone just give slightest of hints as to what type of problemset is coming our way tommorrow

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    8 days ago, # ^ |
    Rev. 3   Vote: I like it +5 Vote: I do not like it

    What do you think their replies would be ...other than "Some Interesting Problems".

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      8 days ago, # ^ |
        Vote: I like it -62 Vote: I do not like it

      but still it would be much better if we get to know type of problems.maybe tiniest of clues

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

        "maybe tiniest of clues"

        Idk why.. but this sounds so-fuccin-funny..

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      8 days ago, # ^ |
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      their*

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    8 days ago, # ^ |
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    Generally testers don't give that kind of hints before contest..

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

    Sure. I was a tester. I can tell you. The problems are interesting. Have fun!

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    7 days ago, # ^ |
      Vote: I like it +20 Vote: I do not like it

    I'll give you a hint for the next 100 rounds, I know, even better. You'll see greedy, constructive, more greedy, elementary math, guesswork, and greedy. You only have a chance at an actual cs problem if you can make it to the last problem, otherwise you'll write 20 lines of code since people on a platform called "code"forces do not enjoy coding.

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      7 days ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      Let me guess, F is your favourite problem in the contest?

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        7 days ago, # ^ |
        Rev. 2   Vote: I like it +7 Vote: I do not like it

        I'm too dumb to get to it. But I saw by your comment you thought it wasn't great ig :(

        But i'd rather code 30m for boring problem (though it is probably not boring for me) than not code at all. So probably.

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Highly disagree. There's a fair amount of regular coding at a regular software engineering job. There are tons of "put a twist on a standard CS algorithm"-type problems on Leetcode.

      This is the only place with such a high ratio of actual problem solving / lines of code. Let's keep it that way.

      This contest wasn't the best one, but not because the implementations happened to be short. There are plenty of other contests with problems with similarly short implementations but that were nonetheless elegant and delightful.

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      7 days ago, # ^ |
        Vote: I like it +1 Vote: I do not like it

      I agree not many problems related to Binary Search, Graphs Algorithm etc. nowadays....

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8 days ago, # |
  Vote: I like it -22 Vote: I do not like it

is it unrated?

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8 days ago, # |
  Vote: I like it +9 Vote: I do not like it

Dude loves physics so much, he used it as his username, pretty sure some physics related questions,any ways good to have frequent rounds.

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    7 days ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    And if tourist were the problem setter you would expect problems themed around sightseeing tours.

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8 days ago, # |
Rev. 2   Vote: I like it +51 Vote: I do not like it

Add the scoring distribution. If you can solve all the problems in a moment, you'll achieve exactly 10000 pts!

Auto comment: topic has been updated by physics0523 (previous revision, new revision, compare).

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8 days ago, # |
  Vote: I like it 0 Vote: I do not like it

All the best and hoping for a great round!!

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8 days ago, # |
  Vote: I like it +3 Vote: I do not like it

Thank you for these frequent contests. we keep on learning and testing our skills it's really helpful

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8 days ago, # |
  Vote: I like it +33 Vote: I do not like it

Do we need to practice HC Verma or Irodov?

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    8 days ago, # ^ |
    Rev. 2   Vote: I like it -42 Vote: I do not like it

    This Comment is Deleted Due to negative feed back, don't know why but my comments are getting down votes all the time, even though the content of my comments are genuine & accurate. From now on I decide to never give any suggestion to anybody on codeforces in the form of comments , because I may not be intelligent enough to give suggestions to most of you.

    thanks!

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8 days ago, # |
  Vote: I like it +28 Vote: I do not like it

I have participated in the writer's contests on another platform (Hackerrank), and his problems are always well-prepared and fun to solve.

I believe this round is going to be great as well!

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8 days ago, # |
  Vote: I like it -13 Vote: I do not like it

Are the problem statements shorter? physics0523

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8 days ago, # |
  Vote: I like it -12 Vote: I do not like it

A contest a day keeps the pressure away.

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8 days ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

what's the meaning of (1500 + 1250) in scoring distribution for 5th problem ? can't we just write 2750 instead? Thanks in advance !!!

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8 days ago, # |
Rev. 2   Vote: I like it +1 Vote: I do not like it

Hope these long queues will be solved as fast as possible. And we will have good contest.

And it is solved :) when i returned to submit the problem after writing comment, it was solved.

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8 days ago, # |
  Vote: I like it 0 Vote: I do not like it

I'm a beginner in CP and became PUPIL in last DIV 3 contest solving 4 problems. Hoping to do well in this contest too. But the problem I'm facing is I'm able to solve A, B in div 2 but on C I always get stuck. So any suggestions how to cover this gap between B and C?

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    8 days ago, # ^ |
      Vote: I like it -8 Vote: I do not like it

    I think the only thing you need , is "practice" .I also in your level & stuck on C.

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      8 days ago, # ^ |
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      Yes, I am practicing a lot. And when I see solutions of C then most of the time I find a new concept which I don't know and then I try to learn that from youtube or from somewhere else.

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7 days ago, # |
  Vote: I like it +22 Vote: I do not like it

2 hours remaining to start the round. But wrong division cases on Codeforces Round #653 (Div. 3) is not fixed yet. Some experts get their rating changed. Will it be fixed before the round starts?

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    7 days ago, # ^ |
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    Maybe they registered for div3 round before they became expert.So they were not out of competition.

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      7 days ago, # ^ |
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      Yes i know that. But as far i know mike fixes it manually at the time of rating change.

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    7 days ago, # ^ |
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    Who cares?! ))

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      7 days ago, # ^ |
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      Some expert may solve the round carelessly since the round is not rated for him. They might care about unwanted rating change.

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7 days ago, # |
  Vote: I like it -43 Vote: I do not like it

making the start 25m later would be perfect!

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7 days ago, # |
  Vote: I like it +13 Vote: I do not like it

Hope the contest will be as interesting as the score distribution .

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7 days ago, # |
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I hope in this round "in queue" will not be shown for longer time

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7 days ago, # |
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how can someone become a tester .... i want to experience being a tester

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7 days ago, # |
  Vote: I like it +2 Vote: I do not like it

Hlo Guys. I am new here. What is the meaning of score (1500 + 1250) of 5th question?

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7 days ago, # |
  Vote: I like it 0 Vote: I do not like it

Hope to become green

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7 days ago, # |
  Vote: I like it +44 Vote: I do not like it

I don't like this round at all...

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7 days ago, # |
  Vote: I like it +78 Vote: I do not like it

And why did Akari have to make the E1 problem difficult? She should have kept quiet. Damn these front bench kids!!

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7 days ago, # |
  Vote: I like it -8 Vote: I do not like it

yes keep changing time by one hour. Great.

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7 days ago, # |
Rev. 2   Vote: I like it +91 Vote: I do not like it

No offense to the round writers, but problem B needs to be proofread by a native or advanced English speaker.

Edit: To clarify, I think the problems are interesting as always, but the phrasing and typos make the problem difficult to read for someone not familiar with the idea of the problem.

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    7 days ago, # ^ |
      Vote: I like it +9 Vote: I do not like it

    I was just going to say this. If there are going to be any rounds in English, it is best they are authored properly. FFS!!

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    7 days ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    Russian statement wasn't great either.

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7 days ago, # |
  Vote: I like it +43 Vote: I do not like it

Good-bye my rating!

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7 days ago, # |
Rev. 2   Vote: I like it -72 Vote: I do not like it

Very Bad round with 90% maths

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    7 days ago, # ^ |
      Vote: I like it +116 Vote: I do not like it

    If you call these problems math, show at least one round which isn't math

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      7 days ago, # ^ |
        Vote: I like it -22 Vote: I do not like it

      that's cause all cf rounds are too math based.

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    7 days ago, # ^ |
      Vote: I like it +21 Vote: I do not like it

    The first question was basic arithmetic, we can't complain. 2nd question required you to know sum of first n Natural numbers which was also not any tough maths. C was casework, D was pattern. Why are u complaining?

    (pls correct me if I'm wrong somewhere)

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7 days ago, # |
  Vote: I like it -37 Vote: I do not like it

Mathforces :(

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7 days ago, # |
Rev. 2   Vote: I like it +57 Vote: I do not like it

It seems like I am the only one who liked the contest. ??? Feel free to downvote if you disliked it. IMHO it is a balanced contest and it is not that MathForces as some of you think.

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

    I don't feel like it's a mathforces round at all. For me it's just easy problems with many corner cases and very unlikeable implementation. In C 4 i got WAs and my AC code is just 7 if statements

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    7 days ago, # ^ |
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    For me it felt like mathhomeworkforces. I did not have any programming problem, it was all logic and E some formular.

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

Interesting problems, but Im too bad for them(

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7 days ago, # |
  Vote: I like it +155 Vote: I do not like it

WTF is going on with this comment section? Round isn't over yet

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7 days ago, # |
  Vote: I like it -20 Vote: I do not like it

b,c problems are real shit. worst ever problem set. All problems are observation based no logic and maths needed.

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7 days ago, # |
  Vote: I like it -17 Vote: I do not like it

I hate this B why I can't solve it spent the whole time on it :(

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7 days ago, # |
Rev. 2   Vote: I like it +54 Vote: I do not like it

I'm curious how the testers easily understood problem B and didn't they feel D is too easy for div2D??

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7 days ago, # |
  Vote: I like it +6 Vote: I do not like it

this contest was difficult for me

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7 days ago, # |
  Vote: I like it -36 Vote: I do not like it

Someone published the solutions :https://www.youtube.com/watch?v=fiPIWx88o_8 the round should be unrated !

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    7 days ago, # ^ |
      Vote: I like it +183 Vote: I do not like it

    Why, so that every time someone has a bad performance they can make the round unrated by uploading solutions?

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      7 days ago, # ^ |
        Vote: I like it -38 Vote: I do not like it

      The round is going to become unrated? :(

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      7 days ago, # ^ |
        Vote: I like it -14 Vote: I do not like it

      thank you man i am very angry and nervous because it was the first contest in which my rating would have increased by 150+ ... and then i come to know that there was some kind of cheating ....hmm i am very disappointed .... for credibility plz check my graph i have worked my ass off hmmmmmm...

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      7 days ago, # ^ |
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      No. That guy was livestreaming his solutions on youtube (from start ). But I'm honest and didn't visit the site and solved what i could myself.

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        7 days ago, # ^ |
          Vote: I like it +10 Vote: I do not like it

        I'm not saying that's what happened here. But I am saying that if you make a round unrated if there are cheaters, then every round will be unrated.

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    7 days ago, # ^ |
      Vote: I like it +47 Vote: I do not like it

    It was travisscott as it can be seen at 26:48.

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    7 days ago, # ^ |
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    That's why number of LOSERS solving problem E increased exponentially suddenly at a certain point of time!!

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      7 days ago, # ^ |
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      CF predictor shows -2 rating for me, damn if cheating happened like that, I'm happy with this rating xD

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

      In the video, only A, B and C were solved (and there were also two failed submissions on D).

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    7 days ago, # ^ |
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    Due to actions of some of these people whole community suffers.Something should be done against them so that this is not repeated.

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    7 days ago, # ^ |
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    The account in the video was of travisscott Action should be taken

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Even if someone has posted the solutions, please do not share that in comments so that others can see those too during the contest!

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7 days ago, # |
  Vote: I like it +2 Vote: I do not like it

What is the pretest 2 for D?

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    7 days ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    Try with: 5 10 Output should be 0 11000 01100 00110 00011 10001

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      7 days ago, # ^ |
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      i see, how did you solve D

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

        This problem is kind of similar to the popular N-Queens problem with some changes. I followed almost the same analogy, but I was a bit worried. And the solution got AC in the main tests! *_*

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

      Oh, how I didn't get it. But how to implement it so?

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      7 days ago, # ^ |
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      My solution gives correct answer for this case but fails on pretest2:(

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      7 days ago, # ^ |
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      i tried to fill the grid diagonally and didn't realize this case

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The contest was really impressive and fun.

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7 days ago, # |
Rev. 2   Vote: I like it +29 Vote: I do not like it

ObservationForces

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7 days ago, # |
  Vote: I like it +18 Vote: I do not like it

ConstructiveForces

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7 days ago, # |
  Vote: I like it +108 Vote: I do not like it

Did I accidentally open Codechef today for the contest?

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    7 days ago, # ^ |
      Vote: I like it -20 Vote: I do not like it

    how would we know also are you blind?

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      7 days ago, # ^ |
        Vote: I like it +36 Vote: I do not like it

      Codeforces Rule #343: Ignore comments from unrated accounts

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        7 days ago, # ^ |
          Vote: I like it +43 Vote: I do not like it

        Codeforces Rule #434: Ignore comments from Master accounts registered 2 months ago

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        7 days ago, # ^ |
          Vote: I like it -12 Vote: I do not like it

        Irony is you are the one breaking that rule

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7 days ago, # |
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I feel bad for the problem writers because of the people who posted the solution to the contest on youtube.

On an unrelated note: is the contest going to be unrated?

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Plagiarism is checked I guess. So all those who copied will be anyway disqualified

    Please look into it MikeMirzayanov physics0523

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      7 days ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      Even then, you still could've gotten the gist of the solution of the problem and simply rewrote the code with your own style. It's also extremely difficult (basically impossible) to check for plagiarism if you submit with another language.

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

        Especially the first 3 problems were just math formulas which are very hard to be checked for plagiarism.

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      7 days ago, # ^ |
        Vote: I like it +57 Vote: I do not like it

      We found the cheater, too. If some users copied some solutions, the plagiarism checker will work.

      I think the contest will be still rated because sadly there are always some cheaters.

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        7 days ago, # ^ |
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        Even He cheated with youtube live.But got +543 ..Cheating is easy now :v And my some friend copy and change some variable , not caught by checker ! Is plagiarism jokes ?

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      7 days ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      Don't count on that. it's very easy to beat Plagiarism testing of codeforces.

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      7 days ago, # ^ |
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      Dude, no offense but do you really think plagiarism will work in these ad-hoc type problems ? Both B and C are have simply 1 liner solution. How will plagiarism work in this case ?

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7 days ago, # |
  Vote: I like it +23 Vote: I do not like it

I don't know if this was intended or not, but I literally solved problem B using the samples without thinking in the main problem.

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    7 days ago, # ^ |
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    I did that for A. :) Sample test cases clearly showed (n+1)/2 if one notices carefully.

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7 days ago, # |
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Nice contest, easy D. I got pretest 9 failed for problem E1 anyone has a clue about that pretest

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7 days ago, # |
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How to solve D? Greed- fill diagonally then it's left and right diagonal and so on...is giving wrong

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

    the idea is ok but when you reach the cell (n-1,n) have to finish with the cell(1,n) and so on (apply modulo when you reach n)

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Try 1 3 6

    Your code will return 4 110 111 011

    while it should return as mentioned: 0 110 011 101

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7 days ago, # |
  Vote: I like it +9 Vote: I do not like it

Was C really just casework? (that's how I did it but..). I hate such questions, wastes time, and morale. Couldn't solve D due to it :(

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    7 days ago, # ^ |
      Vote: I like it +25 Vote: I do not like it

    My observation was that it's always optimal to put all the type 2 people first. The reasoning is that since they always take from the smaller pile, then the size of the pile they'll take from will be $$$x, x-1, x-2, ...$$$ (if $$$x$$$ is the original size of the smaller pile). The larger pile will never be taken by the type 2 people until its size is less than or equal to the size of the smaller pile, resulting the continuation of the sequence. Hence it's never better to put type 1 people first.

    The yes condition ends up being a+b >= n+m && min(a, b) >= m.

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7 days ago, # |
  Vote: I like it +5 Vote: I do not like it

I solved B completely based on the sample cases. I have no idea what does the problem say! I just make it work on samples, I do not know if I am gonna pass system tests or not.

anyways, thanks for the round authors and testers.

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7 days ago, # |
Rev. 2   Vote: I like it +10 Vote: I do not like it

can someone tell me why my E1 solution fails at pretest 9 ?

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7 days ago, # |
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what the solution for E without the f(x) and prime thing

i mean if the problem was just how to find number of permutation?

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7 days ago, # |
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How to solve E1 ? Can someone point me my mistakes ?

int n, k;
vector<int> a; /// size n || sorted
bool solve(int x)
{
    int res = 1;
    for (int i = 0, p = 0; i < n; ++i, ++x)
    {
        while (p + 1 < n && a[p + 1] <= x) p++;
        res = (1LL * res * (p - i + 1)) % k;
        if (res == 0) return false;
    }

    return true;
}
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    7 days ago, # ^ |
    Rev. 2   Vote: I like it +1 Vote: I do not like it

    I think your mistake is in these lines

    for (int x = max(k, mx + 1); x <= n; ++x)
            res.push_back(x);
    

    You only need to iterate to mx. That's enough. So basically erase these lines

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Yes, removing it give me AC, how stupid I was. Thansk for pointing out my mistakes

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7 days ago, # |
Rev. 5   Vote: I like it +6 Vote: I do not like it

In problem B, The picture in sample test case changed during the contest. Initially there were only 3 green ticks. At the end of the contest, there were 6. This created confusion.

Proof-

During contest-Link

When I saw after the contest-Link

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

    Yes. The green ticks confused me (no matter how many they had). The clearest representation would be to group the pictures into 4 categories to show which ones are the same.

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    7 days ago, # ^ |
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    Yes u noticed tooo

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7 days ago, # |
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Back to specialist, RIP rating -100 :(

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    5 days ago, # ^ |
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    back to pupil,-127 :( all because of that problem B statement

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7 days ago, # |
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Understanding problem B's statement alone should be rewarded with +50 rating

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    7 days ago, # ^ |
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    gimme that rating, I understood the problem in one go. (cuz i read it too slow)

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7 days ago, # |
  Vote: I like it +33 Vote: I do not like it

I usually don't comment on the quality of rounds, but I think this round was really bad. A — C are just formulas and cases, and D is constructive. You literally could know zero algoritms, even not know binsearch and sorting, and still solve A — D, and this is really bad in my opinion.

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7 days ago, # |
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First time I solved 4th, Thanks physics0523, you also gave the overflow details in testcase, thanks for that too, Last time I wasn't able to solve due to overflow.

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7 days ago, # |
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Can anyone explain why submission no. 85677436 for problem B of this contest is wrong? While solutions with similar code are accepted.

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7 days ago, # |
Rev. 2   Vote: I like it 0 Vote: I do not like it

I used floor((n-1)/2) + 1 as my answer but this failed on pretest 3. I wonder why? Even in the editorial, same solution is mentioned. I give (n-1)/2 + 1 it passes. Where is the mistake?

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    7 days ago, # ^ |
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    return type of floor is a double type. So if the returned value is large it will be printed in scientific notation (like 5e+008). where as when you do (n-1)/2 the result will remain an integer type and all its digits will be printed as normal integer.

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7 days ago, # |
  Vote: I like it +252 Vote: I do not like it

F: Think for 0.2 seconds and implement for 30 minutes. What an amazing problem.

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7 days ago, # |
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7 days ago, # |
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What the hell was this round OP. Is this a math competition or coding competition???

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7 days ago, # |
  Vote: I like it +31 Vote: I do not like it

Most Ad-hoc round I have ever given on CF.

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7 days ago, # |
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A difficult contest compared to last few div2 contests.

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7 days ago, # |
  Vote: I like it +116 Vote: I do not like it

Problem B was written terribly and also sample explantions were really bad. I won't say that the round should be unrated but it was one of the worst rounds by far in terms of problem statements.

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    7 days ago, # ^ |
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    Misunderstood the problem and wasted a lot of time. RIP rating

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      7 days ago, # ^ |
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      RIP English first... The diagrams were so confusing I just guessed formulas and hoped to get one that works.

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    7 days ago, # ^ |
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    Totally agree. Things were terribly written in the problem B. Was the problem B made to check English and patience of people? One-liner formula was the answer after reading the worst problem statement.

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Exactly. What the hell did the green ticks mean ? He could have simply showed the correct 4 out of 6 in green ticks if at all that's what the author wanted to show. I was scratching my head for 10 min over that.

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      7 days ago, # ^ |
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      yeah, ticks just messed up the statement further

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7 days ago, # |
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Boring contest

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7 days ago, # |
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I hope that someone will have a good proof that why it was optimal to start with type 2 People in Problem C ! I am not able to reason it out! why Starting with Type 1 people is not optimal !

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    7 days ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    My logic was that you can shove your unwanted cookies at type 1 at the end, and they'll eat anything.

    So, you should give your rarer cookies to type 2 people first

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    7 days ago, # ^ |
    Rev. 2   Vote: I like it +1 Vote: I do not like it

    Its because type 1 people always chooses the cookie which is left MORE so they will never get angry if a cookie is left no matter v or c. Type 2 people choose the cookie which is left LESS so they will get angry if the cookie which is left less is finished. Attaching my code for your reference https://codeforces.com/contest/1371/submission/85648596.

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      7 days ago, # ^ |
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      i understand the idea ! But during the thought process I had in my mind that during all this If we feed all the TYPE 2 people first their will come a time where The ratio of cookies will reverse ! And That can happen quite some times during this procedure how to deal with it ?

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        7 days ago, # ^ |
          Vote: I like it +1 Vote: I do not like it

        Type 2 people are sadists they will try to eat up the cookies which are already less. So the number of both the cookies should at least be equal to the no of type2 ppl. The ratio won't reverse as type 2 will go on consuming the less cookies making it lesser.

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    7 days ago, # ^ |
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    Type 2 people consume the cookies that are minimum in number. Suppose you reach a state where both cookies are equal and you have only type 1 people left : then they keep consuming alternatively till both become zero. But the type 2 people consumption is skewed. Since they keep consuming the lowest available cookies, they will run out of the cookies if (min(a,b) < num(type 2 people)). So I wouldn't start with type 1 because they are agnostic of either chocolate cookies or vanilla cookies. They keep consuming. But type 2 nope they see which is lowest.

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7 days ago, # |
  Vote: I like it +13 Vote: I do not like it

What was B? I didn't even go further after reading 4 lines. Highly unclear. Problems must be easy to understand but hard to solve. Seems this was reversed.

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    7 days ago, # ^ |
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    A terrible problem, that's what it was. No coding, just math. Combined with the cheating that took place during this round, it should be unrated.

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    7 days ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    B was like 5 lines of code wrapped in a ambiguous and confusing problem statement.

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7 days ago, # |
Rev. 2   Vote: I like it +9 Vote: I do not like it

For question E, I have a claim that the answers are consecutive if there exists any. Can I ask for a proof / disproof of this claim?

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    7 days ago, # ^ |
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    Suppose that $$$x$$$ is the smallest positive number where f(x) is greater than 0 (In other words, $$$x$$$ is the smallest possible amount of candies you need to start with so you can beat all the opponents).

    Suppose that $$$y$$$ is the smallest positive number such that if you start with Y candies, then at some point of time, You'll be able to fight at least $$$p$$$ opponents and win.

    The answer lies between [x,y-1] inclusively.

    for any $$$z$$$ < $$$x$$$ has f(z) = 0, so divisible by p, so [0,X-1] is totally unacceptable answer

    anything greater than or equal to $$$y$$$ has f(z) = k * p, which is divisible by p , so [Y,infinity] is also unacceptable answer

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      actually, imo proving $$$f(z) = kp$$$ for $$$z \geq y$$$ is not trivial

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        7 days ago, # ^ |
        Rev. 2   Vote: I like it +3 Vote: I do not like it

        But it's trivial to prove that $$$f(z) = kp$$$ for $$$z \ge 10^9$$$. Since, $$$f(z) = n!$$$ and given that $$$p \le n$$$, $$$f(z) \mod p = 0$$$

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    7 days ago, # ^ |
    Rev. 6   Vote: I like it +10 Vote: I do not like it

    let $$$g(i)$$$ be the number of possible choices of $$$P[i]$$$ ($$$1$$$-indexed) for some $$$x$$$
    you can prove that $$$g(i)$$$ is the same for any valid prefix $$$[1, i - 1]$$$ of $$$P$$$
    obviously the number of permutations is the product of all $$$g(i)$$$
    you know that $$$g(n) \leq 1$$$ (since only 1 integer remains), $$$g(i) \geq g(i - 1) - 1$$$ (because you can still choose all the indices that were valid for the position $$$i - 1$$$, except $$$P[i - 1]$$$)
    so the values assumed by $$$g$$$ are consecutive, and if an $$$i$$$ such that $$$g(i) \geq p$$$ exists, a $$$j$$$ such that $$$g(j) = p$$$ also exists
    an $$$x$$$ isn't valid if there is some $$$i$$$ such that either $$$g(i) = 0$$$ or $$$g(i) = p$$$
    let $$$l$$$ be the maximum $$$x$$$ such that a $$$g(i) = 0$$$ exists, for $$$x' < x$$$, $$$g(i) = 0$$$
    let $$$r$$$ be the minimum $$$x$$$ such that a $$$g(i) = p$$$ exists; for $$$x' > x$$$, $$$g(i) \geq p$$$, so there is some $$$j$$$ such that $$$g(j) = p$$$
    so the only valid answers are in the interval $$$[l, r - 1]$$$
    these values are all valid because $$$l$$$ is maximum and $$$r$$$ is minimum

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    7 days ago, # ^ |
    Rev. 3   Vote: I like it +10 Vote: I do not like it

    Proof by AC: 85713453 (find minimum value in easy O(N), binary search to find the max value that works, print every number in between).

    Will update with my "proof" later.

    Proof:

    • Claim: f(x) can be written as some factorial, lets call it X!, multiplied by some mumbers <=X.
    • You can see that this is true when you calculate $$$p_i$$$, the number of possible numbers to go in the $$$i$$$th spot, after you've determined the first $$$p_0$$$ to $$$p_{i-1}$$$. f(x) equals $$$p_0 \cdot p_1 \cdot \ldots \cdot p_{n-2} \cdot p_{n-1}$$$. $$$p_i$$$ is calclated by (the number of numbers in the array <= x+i) — i. $$$i$$$ increases by $$$1$$$ each iteration, and because that is the only way for $$$p_i$$$ to decrease, is impossible to decrease by more than $$$1$$$. There is $$$1$$$ possible number that can go in the last position because only $$$1$$$ number is left, so the $$$p_{n-1}$$$ must equal $$$1$$$.
    • Thus, say you found the position with the maximum number of possibilities had $$$X$$$ possibilities, f(x) = X! * {some numbers <= X} because all numbers between $$$1$$$ and $$$X$$$ inclusive must be represented in $$$p_0$$$ to $$$p_{n-1}$$$.
    • This is important because you can say that $$$f(x)$$$ is divisible by all primes $$$<= X$$$ and not divisible by any primes $$$> X$$$, where $$$X$$$ is the number of possibilities of the index with the most possibilities.
    • You can also show that the $$$X_a \le X_b$$$ for all $$$a < b$$$. This is because having a greater value of x in f(x) will never result in less possibilities for any position.
    • Thus, for all $$$f(a)$$$ and $$$f(b)$$$, where $$$a < b$$$, if $$$f(a)$$$ is divisible by $$$p$$$, then $$$f(b)$$$ must also be divisible by $$$p$$$. $$$X_a$$$ is $$$> p$$$, and since $$$X_b \ge X_a$$$, $$$X_b > p$$$ as well.
    • Starting from the minimum working $$$x$$$ (before of which $$$f(x)$$$ is all $$$0$$$), no value of $$$x$$$ after the first non-working $$$x$$$ can work, so the answer must be in the form of a continguous sequence of numbers.
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7 days ago, # |
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It is ironical that someone who has physics in his username loves math!!!

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7 days ago, # |
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physics0523 write code for problem F. then he write problem for his code

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7 days ago, # |
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Such a shitty round.

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7 days ago, # |
  Vote: I like it +18 Vote: I do not like it

Terrible legends to problems, most of the time was spent on understanding the statesment((

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

    yes bcoz of this I wasted more than 1 hour on 2nd question and this made this round very bad for me

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7 days ago, # |
  Vote: I like it +11 Vote: I do not like it

A lot of Observational questions. If it hits , you could get AC in 5 mins, otherwise many kept scratching, like me.

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    7 days ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Accurately put. That's exactly how it was. Hit the idea or hit the right youtube link. XD

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    7 days ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    I'm pretty bad at Observational questions. Is there any tag related to such problems? I want to solve them. Problem like problem C, I mean.

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7 days ago, # |
  Vote: I like it -11 Vote: I do not like it

Worst contest ever :/

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7 days ago, # |
Rev. 2   Vote: I like it -12 Vote: I do not like it

logic in Problem D is the same as this problem from recent div3 contest

https://codeforces.com/contest/1360/problem/G

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7 days ago, # |
Rev. 4   Vote: I like it 0 Vote: I do not like it

Can someone explain to me the solution to A? I used n / 2 with ceil.

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    ans = n / 2 + n % 2, because if n is odd, then we have 1 + (n — 1), 2 + (n — 2) ... n

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      7 days ago, # ^ |
        Vote: I like it +3 Vote: I do not like it

      or simply just (n+1)/2 as languages round down during division.

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    print each test-case output in newline.

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Use ceil(n*1.0/2) it will work

    In your case, you are using n/2 which will be treated as int and to make it float multiply it with 1.0

    if n=5 your answer will be ceil(5/2)=ceil(2)=2
    but it should be 3 as ceil(5*1.0/2)=ceil(2.5)=3

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      n was declared as float. I used ceil(n/2.0).

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        7 days ago, # ^ |
          Vote: I like it 0 Vote: I do not like it

        float can't accurately represent all numbers up to 10^9. Needs to be double or done via integer maths.

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

        you are printing all answers in same line

        print them in different lines

        cout<<ceil(n/2.0)<<endl; //use this

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7 days ago, # |
  Vote: I like it +1 Vote: I do not like it

Question B was not clear. In the first sample test case,they should have clarified that the 4th and 5th picture are also same (they have different r thats why they should be different). Wasted more than 1 hour on it (I figured the formula in 2minutes) and could not touch C and D properly. Plz,clarify these things.Even on asking the jury ,it said only the last picture(for 1st sample test case) is not considered but actually the last 3 pictures were not considered in the answer.

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7 days ago, # |
  Vote: I like it +2 Vote: I do not like it

I hope Editorial has some brilliant solution for F. Otherwise it is one of the worst problems I've seen in a while.

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7 days ago, # |
  Vote: I like it +12 Vote: I do not like it

I guess it will be hard to believe the testers that comment "problems are very interesting" after this round:(

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7 days ago, # |
  Vote: I like it 0 Vote: I do not like it

Very good round!

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    7 days ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I think that it is in a sarcastic way!

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      7 days ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      The first three tasks were really easy. But I misunderstood the second task, and because of this I passed it at the 65th minute. If I would immediately understand the second task, then I would solve it much earlier and, possibly, would pass the 3rd task. :(

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7 days ago, # |
Rev. 4   Vote: I like it +100 Vote: I do not like it

Some of the shortest code for A-C that I've seen...

A: (n+1)/2

B: r >= n ? (n*(n-1)/2 + 1) : (r*(r+1)/2)

C: (a+b < n+m || min(a, b) < m) ? "No" : "Yes"

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    7 days ago, # ^ |
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    please can you explain the solution of B and C,

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      7 days ago, # ^ |
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      B: When $$$n > k$$$, then there are $$$k$$$ different patterns, one starting at each different day of the week. When $$$n \le k$$$, you only have the straight line pattern. So for $$$r \ge n$$$, you get $$$1+2+...+(n-1) + 1$$$. For $$$r < n$$$ there will never be enough days in the week for a straight line, so it's $$$1+2+...+r$$$.

      C: The observation was that it's always optimal to put all the type 2 people first. The reasoning is that since they always take from the smaller pile, then the size of the pile they'll take from will be $$$x,x−1,x−2,...$$$ (if $$$x$$$ is the original size of the smaller pile). The larger pile will never be taken by the type 2 people until its size is less than or equal to the size of the smaller pile, resulting the continuation of the sequence. Type 1 people always take from the larger pile, so you'll only fail if you run out of cookies. Hence it's never better to put type 1 people first. You also need to check if there are enough total cookies for all the guests.

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    7 days ago, # ^ |
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    Include D as well :XD

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    7 days ago, # ^ |
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    B should be (r*(r+1)/2), isn't it? Typo?

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7 days ago, # |
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Any idea what does TC4 in E1 looks like?

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7 days ago, # |
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Problem B is absolute trash, super unclear, and boring.
Problem C isn't better. Author, can you tell me what the interesting idea or approach is behind this problem? As for me, it's just about understanding problem statements and implementing stupid case analysis.

You know, >75% of participants solve only A, B, and C. So for them it was a 100% shitty round.

P.S. please never invite AmShZ and noobiesAG as testers anymore, if they find this round "really interesting" and "such a great".

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    7 days ago, # ^ |
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    Solved A in 3 mins from then till now I am unable to cracks B's statement If B & C problems are like that how would anyone solve any on Div 2

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7 days ago, # |
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Even A,B,C Solution found on youtube after 1 hours+ . Link. Please notice .MikeMirzayanov ..Please find all the cheaters or and if not possible hope this contest will be unrated.I know to make a contest, authors made so hard work,, But It is unfair someone copy the solution and take positive rating before our eyes And someone go down for only cheaters and gain negative rating . .

**N.B: I was not submit any solution cause busy sometimes on the contest time.Now i feel good cause some problem statement was unclear too , specially B..the contest was worst overall.

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    7 days ago, # ^ |
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    It's impossible to catch cheaters. The first three problems are a simple formula so you can rewrite it however you want. In addition, many people were confused by the problem statement for B. Many questions were asked with disappointing responses. The problems were of really low quality so many people who usually solved the first 3 questions couldn't even solve 2! This would cause the cheaters to get a lot of positive rating change which is clearly unfair to the community. Thus, I think that we should make this round unrated.

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      7 days ago, # ^ |
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      Yes the jury was badd

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      7 days ago, # ^ |
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      Listen to the community: looking at the comments I can find only 2 which say that they enjoyed the contest (not including testers who apparently have a different taste of problems than we do). Clearly, the contest is disappointing to a lot of people. This can be shown by the contribution of this blog. 5 minutes ago it was at 713 and now it is 683. I think that this round should be unrated

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      7 days ago, # ^ |
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      Its correct.Cheaters solved a,b,c easily.and someone can't solved B with their hard work. So By result cheaters got positive rating and hard worker got negative rating . It's unfair (

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7 days ago, # |
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i solved e2 but i didn t understand problem b:))

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7 days ago, # |
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Wow, Problem F is really constructive. Are there any easy solutions to F? I tried to implement the Segment Tree, but it is too hard (at least in my case)

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7 days ago, # |
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B should have tag unreadbale instead of math.

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    7 days ago, # ^ |
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    The statement for B was very confusing.For the whole contest, I thought that every week that divides the total number of days given, results only in one pattern.

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7 days ago, # |
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So beneficial a round to SegTree-addicts.

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7 days ago, # |
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Thanks for writing the round OP. I hope you don't take the hate comments too personally. I especially liked problem E, thought it was a very neat way of combining primes factorization with sorting/arrays.

Hope you can release more rounds and/or problems like this one :)