Rhodoks's blog

Codeforces Round #810
By Rhodoks, 10 months ago, In English

Hello Codeforces!

We are glad to invite you to our Codeforces Round Codeforces Round 810 (Div. 1) and Codeforces Round 810 (Div. 2) which will be held on Jul/24/2022 17:35 (Moscow time). This round will be rated for participants of both divisions. Participants in each division will be offered 5 problems and 2 hours to solve them. The two divisions will share 3 problems.

The problems are prepared by me and zxyoi. We hope that everyone will enjoy this round!

We are sincerely thankful for the help provided by:

We tried our best to have detailed, clear, and short statements. I think that anyone can find some interesting problems in this contest. We suggest to read all the statements.

The score distribution will be announced later.

Wish you good luck and high rating!

UPD

For some reason, we have removed one of our problems. So now participants in each division will be offered 5 problems and 2 hours to solve them.

The score distribution is:

Div2: $$$500-1000-1500-2000-3000$$$

Div1: $$$500-1000-1750-2000-2750$$$

We have some more testers now, let's thank them!

UPD2

We adjusted our score distribution slightly.

UPD3: the Div. 1 part of the round is declared unrated.

UPD4

Sorry for the late editorial.

UPD5

Congratulate to winners:

Div1

  1. nantf

  2. ko_osaga

  3. Rebelz

  4. The_Noble_Brahman_Bison

  5. greenheadstrange

Div2

  1. csyakuoi

  2. Linkus

  3. yaoxi

  4. RGB_ICPC1

  5. bajablast

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

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10 months ago, # |
  Vote: I like it +40 Vote: I do not like it

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

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    10 months ago, # ^ |
    ← Rev. 3   Vote: I like it +37 Vote: I do not like it

    Have a look here before downvoting this blog. I don't think Rhodoks has anything to do with whatever happened with div1 E.

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      10 months ago, # ^ |
        Vote: I like it -24 Vote: I do not like it

      I don't suppose you can differentiate it. Maybe Rhodoks deserves it, maybe he doesn't. That's not the point. The point is the contest is flawed, so it's announce deserves to be down voted.

      I think whoever copied the problem already got enough condemnation from codeforces coordinators.

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      10 months ago, # ^ |
        Vote: I like it +31 Vote: I do not like it

      It is sad when someone work with you makes a mistake and drags you down to the water .

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10 months ago, # |
← Rev. 2   Vote: I like it +78 Vote: I do not like it

A question: Why do contest organizers encourage contestants to read all the statements when a huge part of users can't even have an idea how to solve at least one problem in the contest or even understand it?

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +338 Vote: I do not like it

    The problem is to problem setter what child is to parent. Of course, you are not willing to let some of your children be ignored.

    And I am sure you can understand our statements easily :)

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      10 months ago, # ^ |
        Vote: I like it +60 Vote: I do not like it

      Still the vitosevski's point is valid. For majority of the users reading the hardest problems before solving the easier ones is a bad strategy, and thus majority of the users won't come to the hardest problems.

      I guess that «We suggest to read all the statements» may well be replaced with «You don't have to solve the problems in the order they are present in the problemset» (which is only useful for those who is writing their first contest, or for everyone else as a reminder).

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      10 months ago, # ^ |
        Vote: I like it +397 Vote: I do not like it

      So are you a kidnapper?

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        10 months ago, # ^ |
          Vote: I like it +47 Vote: I do not like it

        They were just babysitting the problems! stop blaming them for no reason!

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    10 months ago, # ^ |
      Vote: I like it +29 Vote: I do not like it

    there are also instances where for example D < C generally, but only reading C and getting stuck on it would make your delta way lower than what would've happened if you read D and found it easy, getting AC, and so on

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      10 months ago, # ^ |
        Vote: I like it +18 Vote: I do not like it

      instances where for example D < C generally

      which we have a very clear example recently

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      10 months ago, # ^ |
      ← Rev. 3   Vote: I like it +36 Vote: I do not like it

      It's not only when D<C for everyone. Sometimes, D can be easier than C only for you. For example, I came from an IMO background, so I usually find number theory problems much easier than other problems of the same rating. In particular, in Codeforces Global Round 17, I solved D (number theory) much faster than C, which contributes to my increase in rating.

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +11 Vote: I do not like it

    After solving problems upto my usual comfort level, often I find myself making progress on a problem number that I don't usually solve, but the topic is something I'm strong at compared to others. And whenever I solve it, I feel good that I read that problem.

    For eg. if you're very good at geometry than people at your rating (most/all people will likely have such a topic), if you find a geometry problem at E when you can only solve problems till C, then it's a good bet to read all problems.

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    10 months ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    You should have your answer now XD

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10 months ago, # |
  Vote: I like it -28 Vote: I do not like it

Just curious, the number of testers is a bit low? How did you accurately estimate the difficulty value of each problem?

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    10 months ago, # ^ |
      Vote: I like it +90 Vote: I do not like it

    It will increase soon. The testing is in progress and the final score distribution will be decided according to their feedback.

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    10 months ago, # ^ |
      Vote: I like it -25 Vote: I do not like it

    sir why are you impersonating human god mejiamejia???

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10 months ago, # |
  Vote: I like it +150 Vote: I do not like it
As a tester...
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10 months ago, # |
  Vote: I like it +2 Vote: I do not like it

Good luck for everyone ❤

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

Changed my mind. Worst round ever

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10 months ago, # |
  Vote: I like it +52 Vote: I do not like it

Chinese rounds are always frightening, because of the maths involved.

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

    Can't improve if you shy away from Chinese rounds.

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    10 months ago, # ^ |
      Vote: I like it -114 Vote: I do not like it

    Well, it may not be that many math problems in our round. Just give it a try! :)

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      10 months ago, # ^ |
        Vote: I like it +18 Vote: I do not like it

      the "may not be" is killer xDDD

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        10 months ago, # ^ |
          Vote: I like it +3 Vote: I do not like it

        I also think taking the Chinese round will be a big boost and I feel that good thinking skills in maths are pretty good

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10 months ago, # |
← Rev. 2   Vote: I like it -44 Vote: I do not like it

w

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    10 months ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    I think you commented on the wrong blog

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    10 months ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    I see you're using a macro for "MAX", and you have encountered a well known issue with it. If you expand the macro, you get

    return query(ql, mid, left, mid, 2 * index) > query(mid + 1, qr, mid + 1, right, 2 * index + 1) ? query(ql, mid, left, mid, 2 * index) : query(mid + 1, qr, mid + 1, right, 2 * index + 1);

    meaning you recompute one of the queries, resulting in a TLE, an easy fix would be to use the builtin std::max function. Also next time comment on the appropriate blog :p

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10 months ago, # |
  Vote: I like it +131 Vote: I do not like it

Not for nothing I went to math club in 7-th grade

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

2 hours and 30 minutes... then I have to go to bed later

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10 months ago, # |
  Vote: I like it -174 Vote: I do not like it

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10 months ago, # |
← Rev. 3   Vote: I like it -78 Vote: I do not like it

Codeforces is best

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10 months ago, # |
  Vote: I like it +40 Vote: I do not like it

Waiting for tourist Vs jiangly showdown. Will no.1 change in this Chinese round?

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

This contest is longer than typical Div 2 contests. Tbh this is a good thing bc the probs might be more challenging.

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10 months ago, # |
← Rev. 2   Vote: I like it -64 Vote: I do not like it

I wish that everyone was given more than -1000 ratings.

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

Very excited!

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

    Don't worry, such a competition becomes too often, and if the rating was taken away from you, then there is something else. You need to believe for the better.

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10 months ago, # |
  Vote: I like it +39 Vote: I do not like it

Give thanks to MikeMirzayanov, for He is good; For His glorious platforms Codeforces and Polygon are everlasting.

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10 months ago, # |
  Vote: I like it -65 Vote: I do not like it

so if The two divisions will share 4 problems, can i register for both and solve the common problems and get double rating.

I know this might sounds stupid please don't downvote.

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +11 Vote: I do not like it

    If your rating is below CM you won't even be able to register to a div 1 contest and if your rating is equal or above CM you obviously can't register to div 2 contests given that you are a div 1 contestant.

    Edit: Sorry, I think that CM's actually can participate in div 2s, but not when there is a div 1 round going on at the same time.

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10 months ago, # |
  Vote: I like it -101 Vote: I do not like it

有中国人

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10 months ago, # |
  Vote: I like it +11 Vote: I do not like it

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

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

Great Round Hope i'll solve 1++ problems in this round Good luck everyone

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10 months ago, # |
← Rev. 2   Vote: I like it +29 Vote: I do not like it

"We have some more testers now, let's thank them!". Thank you, testers

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10 months ago, # |
  Vote: I like it +30 Vote: I do not like it

waiting for your Codeforces Round #1919

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10 months ago, # |
  Vote: I like it +9 Vote: I do not like it

My first div1 OuO hope to solve 1 problem :p

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +14 Vote: I do not like it

    Div1A is just a Div2C so I think you can do it easily as you were able to become candidate master. Good luck!

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +4 Vote: I do not like it

    Now I think I am not lucky.If the round is rated,I will never participate in Chinese rounds if I don't know the author.

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

Good luck everyone!!!!

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10 months ago, # |
← Rev. 2   Vote: I like it +32 Vote: I do not like it

Is div1C same as div2E this time? The score looks like it might not.

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

    I don't think so, div2E will probably be div1D

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

      looks more reasonable. So they removed this problem from div2E but kept it as div1C.

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

Good luck

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

looking forward to your round

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

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

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10 months ago, # |
  Vote: I like it -138 Vote: I do not like it

Can i get some downvotes please so we bait people to click on view

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

really excited, I hope my rating increases.

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

The title description is too bad

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10 months ago, # |
  Vote: I like it +145 Vote: I do not like it

What happened to div1 E?

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10 months ago, # |
  Vote: I like it +65 Vote: I do not like it

If jiangly knows problem E like everybody else, it looks like he is going to be the new number one player

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    10 months ago, # ^ |
      Vote: I like it +27 Vote: I do not like it

    Maybe he knows but won't be top1 this way

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10 months ago, # |
  Vote: I like it +35 Vote: I do not like it

ToroidalForces

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

    These toroidals made me reread the statement again and again

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

      Sad because if they didn't resort to that terrible formula with mods-that-match-the-extents, I might've stayed with my first/correct read of it. I've worked on stuff with toroidal maps (as an option), it's clear enough to me to simply say that the map/grid wraps around vertically/horizontally/both!

      But no... had to wonder why mod was there, so burned time considering possibility of multiple 'neighbors' telescoping out in all 4 directions (because we overwrite common sense with synthetic stuff all the time here!).

      It's the same sort of terrible where the setter described rotating an array using mod-of-index... like, it's clear to those who already know what rotating is and are only worried about left/right... but otherwise, weird-pseudocode-in-text-form shouldn't be a substitute for clear/standard definitions.

      Don't mind me, just adding a layer of salt to glaze my throne of bricks and clown makeup.

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

        I think it would be easier to understand with mentioning that it is just normal side-neighbours, only with wraparound over borders.

        And with labeling neighbours on the picture with "up", "down", "left", "right"

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10 months ago, # |
  Vote: I like it +89 Vote: I do not like it

the contribution of this post will be negative.

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10 months ago, # |
  Vote: I like it +162 Vote: I do not like it

unratedforces

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

Great problems!

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    10 months ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    The topic span is too large. I feel like I'm in prison

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

    Can you please explain the 4th test case in the sample of Div2C? How is the answer yes for that case? I solved B but couldn't even understand this case of problem C.

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

BruhHHH

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10 months ago, # |
  Vote: I like it +29 Vote: I do not like it

Problem B in div.2 is very hard. Actually ,I didn't like this round(MY OPINION)!!

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +15 Vote: I do not like it

    I think the statement was made more complicated than it should have been.

    Video Solution for Problem B and Problem C

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

      You're right about the statements. Thanks for the video ❤

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

    It is a good problem. The idea is similar to last div4 question in which we think in a manner "what if we terminate at the current point ?"

    we can terminate only after removing one odd degree. so following are options

    option 1: Remove one min odd degree if it exists and terminate
option 2: Remove one min even degree node and one min odd degree node and terminate
option 3: Remove 2 least even degree nodes and one min odd degree and terminate

    so on.....

    I couldn't solve as I constrained myself that I should remove only neighbors of last removed node and complicated things and lost so much time and ended up in runtime error.

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

      Option 2 is redundant. It’s always more optimal to just remove the minimum odd degree so you never want to use operation 2.

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        10 months ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        Yes Option 3 is reductant. Considering 2 least unhappiness even degree nodes is not benificial than one least unhappiness even degree nodes.

        Option 2 of mine is flawed. I constrained myself by deleting only minimum unhapiness even degree node as first node. Actually it can be any even node.

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

          The only two options that need to be considered:

          1. Remove 1 odd degree node.
          1. Remove 2 even degree node that are connected to each other.

          My solution: 165558438

          Your solution probably works too, so there are probably many ways to approach this problem.

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

      Assume total degree is odd (otherwise, the answer is trivially 0), there are really only two options:

      1. Remove a single person with odd degree
      2. Remove two people that (a) share an edge with each other, and (b) both have even degree

      As for why this works, removing a person with even degree will not change the total degree parity (odd stay odd, even stays even), but it does flip the parity of the deleted person's friends (odd becomes even, even becomes odd). Therefore, in order to make the total degree even, you need to either remove a single initially odd person only, or you first remove an even person in order to remove a friend of theirs who was initially even but now becomes odd. There is no other benefit to removing an even person.

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        10 months ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        MB

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        10 months ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        Actually we want total edges to be even according to question If edges are even ==> ans is 0 (trivial case) If edges are odd ==> we need to make it even by deleting vertices.

        case 1) so if we remove odd degree node, we removed odd no of edges. since total edges is odd. (odd — odd = even) we are done

        case 2) If we remove even degree node V, we remove even no of edges. since total edges is odd (odd -even = odd) we are not yet done since total edges is odd, but neighbor's of deleted even node gets their parity inverted(odd becomes even, even becomes odd).

        But there might be improvement to option 1 answer as we have created some new odd degree nodes.` Now you can remove any odd degree node and check if it gives best answer.

        There is no need check delete even degree neighbors(after deleting initial even degree we choose) As these are odd degree nodes before deleting the even node V

        Because unhappiness of the any even degree node(after deletion of vertex V) connected to vertex 'V' is greater than equal to minimum unhappiness of all odd nodes which is case 1 answer. so there is no point in deleting the even degree(after deletion of vertex V) neighbors. Hence the current even node doesn't give best answer and it is not beneficial.

        we do the above process for every even node and this is the best possible answer if we chosen current even vertex as initial vertex

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

          Yeah, basically, there is no benefit to performing case 3 at all. Ultimately, the objective is to remove one odd-degree person.

          If an even-degree person X has all of their friends with odd-degree, then there is no benefit to removing X at all. Removing X changes their odd friends to become even, but we're trying to find odd people, not even people.

          Here is a different angle that you can look at it:

          Let's consider whether the optimal solution involves deleting person i. If person i has odd degree, then removing person i is enough (case 1) and we don't need to get rid of any more people.

          But if person i has even degree, then removing person i isn't enough. We need to delete a friend of person i as well, so that person i becomes odd degree. If we delete a friend j with even degree, then delete i and j is enough (case 2). If, instead, we consider deleting a friend j with odd degree, then deleting j alone is enough (and is already covered by case 1), and it's better to delete j alone than to delete both i and j (and maybe even others). So cases 1 and 2 are all we need to consider.

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10 months ago, # |
  Vote: I like it -6 Vote: I do not like it

done A,B,C

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

Meanwhile Carrot:

image

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

I strongly dislike this round.

  1. B is a graph problem and unsuitably hard. I think it is because they deleted the original problem B and can't come up with a new one.

  2. Unsuitable difficulty. Div.2 D is harder than Div.2 E while Div.1 D is way harder than Div.1 E.

  3. Coincidence. Div.1 E coincides with a well-known problem, which is totally unfair and unexpectable.

I actually hoped that this round will help change the image of Chinese rounds in the community, but in fact, I am wrong.

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    10 months ago, # ^ |
    ← Rev. 8   Vote: I like it 0 Vote: I do not like it

    As a tester (and first time tester), I agree that div1B/div2D is harder than usual, but I think it's a good problem. I solved div1B/div2D in about 80 minutes, and only 3 of the 13 testers (mostly red and orange testers) solved div1B/div2D in the virtual contest. I advised the problem setter add the 4th example of problem D, to give users more hints. (originally it has only first three examples and time limit is 3s). We also increase the time limit of div2B to make it more friendly to python user.

    UPD: I apologize the problem 1E (I thought this problem is far beyond my ability so I didn't make any suggestions about this problem, I should have googled it). It's OK to complain and down vote this contest, even my comments, but please don't say something bad to the Rhodoks himself. He is a very nice person and take our testers suggestions very seriously, and he didn't mean to make a bad contest (he is not the author of 1E). It's just a mistake.

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      10 months ago, # ^ |
        Vote: I like it +9 Vote: I do not like it

      But what about the coincidence of problem E and the unsuitable difficulty of B? Like, now Div.1 D have only several solves while E have almost the same of C. What's the explantation?

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        10 months ago, # ^ |
        ← Rev. 9   Vote: I like it +18 Vote: I do not like it

        We apologize for the problem 1E. None of us solved 1E in the virtual test. I thought this problem was far beyond my ability so I didn't make any suggestions about this. Next time as a tester, I should search each problem by google, even if I am not able to solve this problem.

        The problem setter Rhodoks is a very nice person. We made many advices and he took our advices very seriously, we even remove one problem because one of our testers find this problem not "original". I should have suggested him to add one easy problem to make the contest more balanced.

        I think he wants to make the contest better, not make a bad contest deliberately. We tested this round too late to make adjustments. (like create a new problem) It's pretty sad that he received so many downvotes (even if the notorious div1E is not written by him). My suggestion is that do not down vote his solution post or say something bad to the person himself, it's unfair to him.

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    10 months ago, # ^ |
      Vote: I like it +45 Vote: I do not like it

    But why do you talk about problems here? The contest is running now anyway.

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      10 months ago, # ^ |
        Vote: I like it -51 Vote: I do not like it

      I'm not talking about the solutions, just the problems themselves and stating some facts.

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        10 months ago, # ^ |
          Vote: I like it +6 Vote: I do not like it

        Well, is stating some facts allowed? I think it isn't.

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    10 months ago, # ^ |
      Vote: I like it +2 Vote: I do not like it

    B isn't a graph problem. Simple maths knowledge (about sum of even/odd numbers) can be used to solve the problem.

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

      Yeah, I agree. I also used simple maths knowledge to solve it. However, it is just not suitable and is hard for anyone who isn't familiar to graph to approach, that's the point.

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

      But I think I have to build the graph to solve it.......

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    10 months ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    E for easy, D for difficult I guess.

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

    B is not a graph problem I guess. Hopefully my solution is right and I don't get FST :\

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10 months ago, # |
← Rev. 6   Vote: I like it +35 Vote: I do not like it

Questions about problems

156039 KroosTheKeenGlint

2022-07-24 18:54:49 Problem E. Two Arrays

(Question)

So should I copy a solution from the comment and paste to solve this problem?

Is it really fair?

(Offical Answer)

Yes

156036 KroosTheKeenGlint

2022-07-24 18:53:22 Problem E. Two Arrays

(Question)

What happened with this problem? I see this is coincidence with some other problems.

Is this contest unrated?

(Offical Answer)

The contest is rated.

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10 months ago, # |
  Vote: I like it +9 Vote: I do not like it

this blog will get negative delta contribution after the contest , another unbalanced round -_-

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10 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Unbalancedforces

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10 months ago, # |
  Vote: I like it +31 Vote: I do not like it

SaikeForces

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

I participated in Div.2. The difficulty gap between Problem A and Problem B is too large. Also, Problem D and E are a difficult problem for most people to solve. The problems are good, but the problemset is disappointing :(

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10 months ago, # |
← Rev. 3   Vote: I like it +8 Vote: I do not like it

Why big coordinates in 2D/1B ? It only makes the problem (way) more painful, and I'd rather go kill myself than writing it.

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10 months ago, # |
  Vote: I like it -33 Vote: I do not like it

Wow greenheadstrange aka amiya solved all problems!!

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10 months ago, # |
  Vote: I like it +94 Vote: I do not like it

Why did problem E exist before??
What will the authors do regarding this??
Should I copy the code of the problem???

A comment above me asked the authors in clarifications (probably) about this problem, they told him he can copy the code to solve this problem, how is this fair??? and even if it is legal, what about plagiarism check???

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10 months ago, # |
  Vote: I like it +67 Vote: I do not like it

F**k U.Really shiiiiit round!!!UNRATED!!!!!!!!

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10 months ago, # |
  Vote: I like it +99 Vote: I do not like it

fku, it should unrated.

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10 months ago, # |
  Vote: I like it +20 Vote: I do not like it

Unbalanced Unbalancedforces

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10 months ago, # |
← Rev. 2   Vote: I like it +23 Vote: I do not like it

...

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10 months ago, # |
  Vote: I like it +428 Vote: I do not like it

Please make this round unrated. Problem E is absolutely unfair.

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    10 months ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    Second.

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    10 months ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    Always choose justice even when compared to great positive delta!

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    10 months ago, # ^ |
      Vote: I like it +82 Vote: I do not like it

    Is it available to copy on some secret Chinese server? :) I participated in that OpenCup and managed to remember/find the problem and then the editorial, but it still would take some time to implement.

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

    Is it possible to just make Div 1 unrated (as problem D1E was publicly available), but keeping Div 2 still rated ?

    As for Div 2, the problems were fine, though not balanced.

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10 months ago, # |
  Vote: I like it +163 Vote: I do not like it

Why not unrated?

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

Guys, you discuss the round too much when it is not even finished

Though I take my words back, apparently div1 has real problems /:

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10 months ago, # |
  Vote: I like it +277 Vote: I do not like it

Petition to make this contest unrated

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10 months ago, # |
  Vote: I like it +78 Vote: I do not like it

Unratedforces

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

lol

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10 months ago, # |
  Vote: I like it +85 Vote: I do not like it

Please make this round unrated

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10 months ago, # |
  Vote: I like it +113 Vote: I do not like it

Everyone is posting spoilers, and nobody's taking actions for them?

It's very unfair if this gets rated, since just looking at the comments will give you a great hint to solving the problem.

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    10 months ago, # ^ |
    ← Rev. 3   Vote: I like it +82 Vote: I do not like it

    It's acceptable if the same problem already exists, it happens. I can understand that.

    But why do people post that fact here? If you know the problem/solution, just get advantage of it. It's obviously against rules to post them before the round ends.

    Serious actions should have been done to delete them as soon as possible, but why did the organizers just leave them be?

    EDIT: Okay, the problem is even copied, what a shame.

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

Really bad round, D and E are absolutely unsolvable for div2 level. It's obvious by the amount of the submissions, 3000 for C and only 50 for D

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

negative delta :(

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10 months ago, # |
  Vote: I like it +14 Vote: I do not like it

Can't wait to see negative votes on this post!

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

    It seems that since several seconds after the contest, the votes have been negative and kept decreasing.lmao.

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10 months ago, # |
  Vote: I like it +201 Vote: I do not like it

Please ban whoever decided it's nice idea to link to the problem before the round has ended.

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10 months ago, # |
  Vote: I like it +29 Vote: I do not like it

If this round is rated, then God really eats shit.

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

I participated in Div.2. There is a dramatical difficulty difference in Div.2 between A/B/C and D/E which made this contest a semi type race. The ranks of people solving three problems are from 60 to 2500 currently so there's the differences between participants are not represented well.

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10 months ago, # |
  Vote: I like it +2 Vote: I do not like it

fk this round

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

Div1 China-sided round

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

Managed to solve D2D @ hope no one bothered to make anti-python-hash-hacks xD

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10 months ago, # |
← Rev. 2   Vote: I like it +215 Vote: I do not like it

When the hardest problem is a well-known problem in China:

Capture

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

    Because many school in China have used this problem for practice.

    So it is well-known.

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

      The 10-th man even wrote a blog for that.

      You could see via this link

      It is under the G.game, you could click the second block under it and see the code.

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

      I've got the info just now.

      Two big mock contest have used this problem, and at least 150 people in China have participate in these two contest.

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +22 Vote: I do not like it

    Chinese reminder theorem.

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

bruh, D is sqrt decomposition. just no time left to write it

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    10 months ago, # ^ |
      Vote: I like it +3 Vote: I do not like it

    My solution is not sqrt . In fact I'm not sure if it is solvable with sqrt. Large constraints on coordinates seemingly prevent it

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

      oh yea, i should read limits with more attention. sqrt is not going to work (

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

        Could you describe your idea if you think it still holds for small coordinates. Just curious, cannot come up with it even for small ones.

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10 months ago, # |
  Vote: I like it +11 Vote: I do not like it

So, if a contestant is reading the comments and thinks this contest will be unrated, so he or she gives up solving the problems (especially for the countries that the time is not usual and they probably need a sleep), and that causes the negative rating change, is it fair???

Well, I'm talking about me myself, but I have also learnt about someone else just like me, including both Div.1 contestants and Div.2 contestants.

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10 months ago, # |
  Vote: I like it +81 Vote: I do not like it

哈哈，原题场，down vote!

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10 months ago, # |
  Vote: I like it +42 Vote: I do not like it

Since many participants may copy E from the Internet, I don't think it fair and rational to make this div.1 round rated.(Though I get +30 to +40)

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10 months ago, # |
  Vote: I like it +183 Vote: I do not like it

Problem E got got 0 solves in the opencup and Suddenly it got 171 AC in the contest.Morever this was informed in the comments as well multiple times.The contest just became finding the right code online in time and should be unrated.

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10 months ago, # |
  Vote: I like it +9 Vote: I do not like it

Please make this round unrated or I will eat shit.

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10 months ago, # |
  Vote: I like it +1133 Vote: I do not like it

What the fuck?

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10 months ago, # |
  Vote: I like it +6 Vote: I do not like it

This post will get more negative rating than my negative delta today. B statement was weird. C was more like "You know then ok" Idk if it actually is a good problem. Couldn't solve C this time. :( IDK if it's me or this contest was not as good as usual contests.

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10 months ago, # |
  Vote: I like it +26 Vote: I do not like it

Unrate this round

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10 months ago, # |
← Rev. 2   Vote: I like it +73 Vote: I do not like it

rnm, 退钱！

fxxk, refund!

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

    退钱退钱！！！推rating！！！

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10 months ago, # |
  Vote: I like it +78 Vote: I do not like it

The author of this contest only know copy?

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

me: Annoying so many 114514 ... => Oh, D1C is amazing, I love it! => WTF D1E, why more than 100AC???

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10 months ago, # |
  Vote: I like it +52 Vote: I do not like it

lmao what the fuck

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

jls is going to be angry for 1E.

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10 months ago, # |
  Vote: I like it +188 Vote: I do not like it

Fun fact: E's Sample and the Format is the same as a "similar" Problem.

Similar Pro:

E:

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

Oh that question B messed up my already messed up rank lol

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10 months ago, # |
  Vote: I like it +27 Vote: I do not like it

BIG difficulty gap between D1A & D1B

and FUCK D1E

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    10 months ago, # ^ |
    ← Rev. 2   Vote: I like it +37 Vote: I do not like it

    Ah, a man of culture I see (prof pic)

    EDIT: No longer xD

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10 months ago, # |
  Vote: I like it +22 Vote: I do not like it

Nothing else but shit.

Unrated, plz.

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10 months ago, # |
  Vote: I like it +71 Vote: I do not like it

OK, I know that Div1E is well known and I was implementing it with the help of the editorial, but I couldn't find the code online. How does it come that 171 people solved it? I wouldn't expect that many even if the statement directly said "It's problem G from GP of Bytedance 2019"

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10 months ago, # |
  Vote: I like it +81 Vote: I do not like it

Opinion: I don't think that the round must be unrated. I would certainly prefer it to be unrated for selfish reasons, and I was angry that E is copy-able or at least googlable and even left the round midway. But I don't think that having a well-known problem is enough to make a round unrated.

Also I don't understand why did people post the link to the old problem in the comments during the round, it feels like a deliberate attempt to make the round unrated.

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

    Facing a well-known problem and knowing it is really well-known and finding that many cheaters are copying the code can make me annoyed during the contest and get a bad performance.

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    10 months ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    Well, I personally think it should be unrated in the case that the problem was intentionally copied from the other source.

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    10 months ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    I can understand the reason: they just misunderstood that the round had already been completely ruined (but actually it hadn't until the link was posted). Of course "deliberate attempt to make the round unrated" might be another reason.

    It made the situation even worse that during the contest people posted comments in the article https://codeforces.com/blog/entry/65510 so it appeared in Recent actions. Contestants who try to look for the problem using Codeforces could accidentally notice it.

    IMHO the situation is similar to the case where malicious people would have done DDoS or whatever to ruin the contest. People who gave information about the problem need to be punished to some extent, and some people (including me) insist the round should be unrated.

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10 months ago, # |
  Vote: I like it +86 Vote: I do not like it

1C= https://blog.csdn.net/qq_35577488/article/details/117813076

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10 months ago, # |
  Vote: I like it -8 Vote: I do not like it

Serious?

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10 months ago, # |
  Vote: I like it -14 Vote: I do not like it

Ggs, gonna lose about 10000000 points

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10 months ago, # |
  Vote: I like it +28 Vote: I do not like it

thanks for the fast Tutorial on problem E

I see a lot of solutions for it in comments when it's still running ... xD

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10 months ago, # |
  Vote: I like it +44 Vote: I do not like it

Trash round and unrate it please.

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10 months ago, # |
  Vote: I like it -13 Vote: I do not like it

These problems were way too hard, I underperformed by a long shot.

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10 months ago, # |
← Rev. 2   Vote: I like it +23 Vote: I do not like it

This is the worst Round I have ever participated in.

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

The contest should be unrated because Div1.E is an old problem and can be found by https://www.acmicpc.net/problem/23679.

The tutorial was public on China before finishing the contest. https://www.cnblogs.com/Flying2018/p/acmicpc2874.html

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    10 months ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Well, it is probably a reason for making div1 unrated (though they could just skip copy-solutions). But it should not affect div2

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

Why so Hard B?

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

Over 100 contestants passed problem E, so this contest must be unrated.

I suggest to ban the discussion of original problems during the contest. With this rule ,contests like this will probably still be rated, because only few people know the original problem, and the result can show the skills of contestants.

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

This contest was very good, my family and I hope you don't play again in the forever!

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

Is Div2 unrated?

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

    Why would it be?

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      10 months ago, # ^ |
        Vote: I like it +17 Vote: I do not like it

      Because Div1 must be unrated,i don't know what will happen on Div2

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        10 months ago, # ^ |
          Vote: I like it +3 Vote: I do not like it

        It would be stupid to unrate div2 because of problems that concern only div1

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

          You have a great result today, would be unnice to unrate it :/ You might get nicer color.

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            10 months ago, # ^ |
            ← Rev. 3   Vote: I like it 0 Vote: I do not like it

            Yeah, if I'm not hacked and the round is rated, I could get back to violet for the first time in years.

            Hacks is a separate story. Since I solved D in python and there is no std::map in python, it can be hacked with some antihash. Knew about it during the round but didn't bother to protect. I just hope that hackers didn't bother about it either

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

I wanted to write normal round and became CM. And what is it? Speedforces and Div 1E is not new tasks. I hate this round.

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10 months ago, # |
  Vote: I like it +137 Vote: I do not like it

Div. 1 E is a total failure. Participating above my average level and then seeing everyone just copying the solution of the hardest problem in the contest from some Chinese server (and thus beating me) completely ruined my day. The round indeed must be unrated. The testing/coordination of the round is done poorly, such coincidences must not happen, it's an abominable situation.

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

In China,SaiKr Round 2 (Div. 1 + Div. 2, Rated)

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10 months ago, # |
  Vote: I like it +9 Vote: I do not like it

There should be atleast one strong Chinese tester in each round.

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

very balanced div2 lmao

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

I don't know why this happened, I was in jail for an hour, what a fuck!!!

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

You can see a bunch of Chinese at the top of div1。funny wow！！！f**k unratedforce

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

https://blog.csdn.net/qq_35577488/article/details/117813076
Problem 1C also can be found on the internet.
This Blog is published on 2021.8.20,with the problem statements and code.
Well, The restriction differs but doesn't matter

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10 months ago, # |
  Vote: I like it +21 Vote: I do not like it

Trash round. I think nearly 90% of people who pass div1. E are looking at the solution. The examples are the same! So trash.

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

Div 2B looked like a graph problem, not being good at graph found some way to solve it without graphs, passed pretest might fail main test. Wish i had gone for c first, overall i feel this contest was really tough

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10 months ago, # |
  Vote: I like it +37 Vote: I do not like it

I'm not expecting this result since you've already removed one problem. :(

PLZ make this round unrated.

By the way, the previous problems (1A, 1B) seems to be good, but problem.E really broke our contest experience.

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    10 months ago, # ^ |
      Vote: I like it -10 Vote: I do not like it

    1B was good? seriously?

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

      Maybe it's a little harder than normal, but since this round is a 5-problem round, I believe that it's at least acceptable.

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

If the round didn't get unrated then atleast delete problem E from calculations of score, Its unfair for a well-known problem to exist as a new problem!

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    10 months ago, # ^ |
      Vote: I like it +24 Vote: I do not like it

    Just wanna throw in, seeing so many people solve div1E (more than div1B) made me invest all my time in E instead of B. Removing E from calculations won't give this time back and I guess others did so too. Just wanted to point this out.

    Either way I agree, I think this round should be unrated [or at least E should be taken out].

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

I hate this round

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10 months ago, # |
  Vote: I like it +50 Vote: I do not like it

Imagine running plagiarism checker on tens of thousands of submissions for hours, when the real plagiarist turns out to be the problemsetter :(

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10 months ago, # |
  Vote: I like it +23 Vote: I do not like it

This is the best round I have ever seen, I can hardly imagine a round with a perfect balance and difficulty, the level of the authors is quite high, all levels of coders were able to get a perfect round, I felt physically and mentally happy when I played this game.

The questions in this cf were very interesting and I learned very many meaningful tricks from them, the difficulty slope was very reasonable, the sample coverage was very wide, and I even got a pass on the sample that only made the code pass.

What I admire about the author is that he has the courage to submit this kind of contest for review. If I had come up with such a topic, I would have been ashamed, but the author is open and honest, a real gentleman, he is the best courageous person I have ever met, bar none.

When I clicked on the leaderboard of the contest, I even wondered if I had clicked on the rating list. other low quality contests had purple and grey in the leaderboard, but in this contest, purple, blue, cyan and green were clearly defined, which made me admire the author from the bottom of my heart.

Finally, I wish the problem setter a long life, a happy family, good health and a speedy recovery from the loss of his mother.

by sora1336 https://codeforces.com/blog/entry/93538?#comment-827037

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

    You should not say anything, about someone's mother, RESPECT EVERYONE

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

o-o I don't think I've ever seen a contest get downvoted so quickly.

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

CN Round qwq

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

Div2B, I actually do not get it. Looking at the codes it seems simple, but I do not understand why they work. What observation do I miss?

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

    if number of pairs is even u can call everyone right? if it is odd u will have to remove 1 pair, so it becomes a greedy as for each pair we check whether to not call first one,second one or not call both.sorry for my bad english.

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

      Why does removing 1 or 2 persons garantee that the remaining number of pairs is even?

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

        It doesn't, you have to greedily find a person (or two) such that removing them makes the remaining number of pairs even. Atleast that's what I came up with during the contest.

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        10 months ago, # ^ |
        ← Rev. 3   Vote: I like it 0 Vote: I do not like it

        it does not guarantee u will have to check,just make a map and keep a count, which number appears in how many pairs for example:

        1 2

        2 3

        2 4

        5 6

        two appears in 3 pairs so i cant remove 2 coz that will leave an odd number of pairs,but removing 1 and 5 is feasible coz that leaves 2 pairs.
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        10 months ago, # ^ |
        ← Rev. 2   Vote: I like it +5 Vote: I do not like it

        If the person appears odd number of times, then it is obvious why it works

        Now what if there are no such people. It means that if you take a pair, both participants appears in pairs even number of times (but one of them is shared!) so that means that if you remove both, you will remove odd number of pairs

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

        If a person has an odd number of friendships, then removing that person removes an odd number of cakes. Therefore, if we started with an odd number of cakes, we now have an even number of cakes.

        If you remove a person with an even number of friendships, you will still remain with the same parity of cakes HOWEVER each friend that had an even number of friendships will now have an odd number of friendships for which you still have cakes to make. And then you're back to the first case (one person with an odd number of friendships).

        There is no other potential optimal move if the initial number m is odd. If you were to remove one that is initially even and then remove one that was already odd before the removal of the first one, then why did you not remove the odd one and leave it at that? Makes no sense either to remove two that don't have a friendship and are both even-friended.

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          10 months ago, # ^ |
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          really appreciate!

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          10 months ago, # ^ |
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          Why can't it ever be the case that we remove 3 people?

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            10 months ago, # ^ |
              Vote: I like it +1 Vote: I do not like it

            Because you can always either just remove 1 of those 3 people(if there is one with odd degree) or 2 of those 3 people(if all have even degree and there is an edge between those 2), otherwise you wouldn't be able to remove those 3 people, and removing only some of the 3 people is obviously better than removing all 3.

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

    If M is even, you don't need to delete any node. Else, you either delete a single node having odd degree or 2 nodes having even degree which are neighbours.. Can you explain for Div2c?

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

    Observe that

    1. If the number of pairs is already even, you don't need to do anything.

    2. On the other hand, if the number of pairs is odd, the answer can be either of the following:

      A. The min unhappiness is achieved by not inviting a person with an odd number of pairs.

      B. Don't invite a person with an even number of pairs. If the number of pairs for any of his friends becomes odd after this, the unhappiness of removing these two people can be unhappiness.

    The minimum overall will be the answer.

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

    If edges count is even, answer is 0. Otherwise, if the optimal solution has an uninvited person with odd adjacency count, it is enough to not invite that person alone. While if all the uninvited persons in a solution have even adjacency count, then at least 2 of them must be adjacent because otherwise the deleted edges count would have been still odd, so it is enough to not invite such 2 persons alone. So the is answer is minimum(minimum unhappiness of a person with odd adjacency count, minimum unhappiness sum of 2 adjacent persons with even adjacency counts).

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

    Hey!

    If m is even, the answer is 0, because we can invite everyone and we will have an even number of eaten cakes.

    If m is odd, then let's try to invite everyone except some guys. We have two options:

    Option 1. Skip one guy:

    Let's take a look at the number of friends that each club member has. If we decide to not invite someone who has an odd number of friends, then we can try to not invite him and get an even number of eaten cakes.

    Option 2. Skip two guys:

    Here we want to remove 2 guys in such a way that after removal there will last an even number of friends invited. Let's consider two friends, such that both of them have an even number of friends. Because both of them have each other as a friend, after the removal of these two guys we'll have an even number of eaten cakes.

    Let's choose the best answer.

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

ABC is solvable, but DE... I think there is a big difference in complexity between C and D.

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

i understand and agree on the fact that contest was not good because of many reasons,but still the kind of comments that we are posting is not at all healthy from a community point of view,so lets give feedback's but in a constructive way as everyone is a human here.Hope u understand my point:).

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10 months ago, # |
← Rev. 2   Vote: I like it +43 Vote: I do not like it

Sparky_Master_WCH1226 is about to lose their bottom contributor spot for a totally unexpected reason (for me at least).

Update: Sparky_Master_WCH1226's bottom contributor spot has been overtaken by the round author.

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    10 months ago, # ^ |
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    I want to take it back!!! It used to be me!!!

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    10 months ago, # ^ |
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    Why is Sparky_Master_WCH1226 contributing so low and what are the reasons?what did he do wrong？

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10 months ago, # |
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Bad Contest, I spent more than 30 minutes to understand B

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10 months ago, # |
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Shame

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10 months ago, # |
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Red also cheats in contest?

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10 months ago, # |
  Vote: I like it -35 Vote: I do not like it

I attribute this failed attempt to reaching Master to Div1E. So close yet so far.

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10 months ago, # |
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what's wrong with my solution for C ? i thought that it's always optimal to color the grid either horizontally or vertically but getting WA on test 2 , Here is my code
165577141

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    10 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it
    TEST1
    TEST2
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    10 months ago, # ^ |
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    You need fill at least two adjacent lines with same color, otherwise you would get only two toroidal neighboors.

    Example: 

    1121
1121
1121

    Is not nice picture

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