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SleepyShashwat's blog

Codeforces Round #682 (Div. 2)
By SleepyShashwat, 4 years ago, In English

Good Evening Codeforces! ^_^

This round is unrated; please read this to know why.

I invite you to participate in Codeforces Round #682 (Div.2) taking place on Nov/13/2020 17:35 (Moscow time). The round, authored by Anti-Light and me, is rated for users rated less than 2100, while other users can participate non-competitively.

The round features six problems, and you have 2 hours to solve them. There may, or may not, be an interactive problem; regardless, you should know how to deal with them.

I would, now, like to thank–

We will announce the scoring distribution shortly. The scoring distribution is 500–750–1250–1750–2250-3000.

Good luck, and stay safe!

UPD: Editorial

For students in high school or below—

Participants who are currently in high school or below are eligible to win prizes — 25 USD gift cards to 5 random participants who solve at least 3 problems. Prizes are sponsored by Athena Education and are NOT related to Codeforces. To be eligible, please fill this form (it will be closed after the round ends). If you're interested in participating in other technical events, such as Machine Learning and Computational Linguistics, please head over to exunclan.com.

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

Comments Comments (194)
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4 years ago, # |
← Rev. 2   Vote: I like it +4 Vote: I do not like it

Registered Participants are eligible for the following prizes.

Registered participants on round or those who filled the form?

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

    Those who filled the form; I have edited the blog to reflect this. Thank you!

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

Hmm, it would have made sense if there were cash prizes for top rankers + random people, or only top rankers. But to have prizes only for random people is a bit weird.

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4 years ago, # |
← Rev. 2   Vote: I like it +18 Vote: I do not like it

Expecting a Good Problem Set. Because it's SleepyShashwat

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

Omg Indian round! So excited

Untitled.png

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

Hope you weren't sleepy while writing problem statements.

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

    He lost a lot of sleep due to problem statements, that's why he's sleepy now.

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4 years ago, # |
  Vote: I like it -141 Vote: I do not like it

.

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

    Seems like first time we are seeing Monogon loosing contribution

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      4 years ago, # ^ |
        Vote: I like it +75 Vote: I do not like it

      I'll have to find a new source of dopamine now

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        4 years ago, # ^ |
        ← Rev. 2   Vote: I like it -32 Vote: I do not like it

        Seems like you already found one, But sadly I have to loose some of my contributions because of above comment. Though I don't care about it(but who doesn't like green++).

        Edit:Also I can see realnimish gaining +47 because of my username, thats interesting. I think people should atleast appreciate my username, if they don't like the comments XD.

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      4 years ago, # ^ |
        Vote: I like it +55 Vote: I do not like it

      Its a trap

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

      You just see he will reply to the comments like yours and get 1k upvotes.

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4 years ago, # |
  Vote: I like it +78 Vote: I do not like it

intresting problems.

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4 years ago, # |
  Vote: I like it +33 Vote: I do not like it

I'm currently in high school but over 2100, so this round will be unrated for me. Will I still be eligible for any prizes?

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

As a tester these problems were very interesting!

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4 years ago, # |
  Vote: I like it +98 Vote: I do not like it
Mandatory meme
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    4 years ago, # ^ |
      Vote: I like it -15 Vote: I do not like it

    yea codforces should provide more contests :,)

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

[Your text to link here...](IMG_20201111_021152.jpg)

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

    I am telling you that cute little face had no idea that round would be unrated.. Though had fun first 10 minutes of rounds..

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4 years ago, # |
  Vote: I like it +135 Vote: I do not like it

Finally!

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

Wow that's a whole lot of testers!

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

Now I am more excited about the 3b1b-style video editorials!!

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

lol, 1 week without contest,

It was difficult, MikeMirzayanov

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

please we request don't take 10 days gap for codeforces contest

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4 years ago, # |
  Vote: I like it +71 Vote: I do not like it

These 10 days made me realise the plight of div 1 users. Guys hats off to your patience (all div 1 users)

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4 years ago, # |
  Vote: I like it -6 Vote: I do not like it

yo 3b1b type videos? that's sick

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

Finally a contest now :)

It seems that there are much more people testing for the contest. So I think this Div.2 would be an excellent one :)

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

    Oh no, it became an unrated contest becuase of B :-(

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

    I think I would like to delete my comment :-(

    Picture below shows how I feel when I saw the announcement that the contest is unrated...

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

Finally something to cheer about

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

Waited)

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

![ ](IMG_20201113_113829.jpg)

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

Wow, there is Anti-Light in writers too!!

I guess this round is going to be awesome.

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4 years ago, # |
  Vote: I like it +22 Vote: I do not like it

Happy Diwali :)

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

They say it's an Indian contest but it isn't just an Indian contest, it's an Indian_Iranian contest. Because Anti-Light is Iranian. So... it means it's gonna be so good.

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

I didn't finish the form which to prove i'm a high school student. Could I finish it now?

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

Happy Diwali Everyone !!

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4 years ago, # |
  Vote: I like it +101 Vote: I do not like it

problems are very sexy 10/10 would bang

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

Is it rated?

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

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4 years ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

happy diwali to everyone out there

this diwali i pray to god so that your code gets compiled and accepted at one go(mine too :) ).

happy diwali happy coding

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

Every body holds his hat XD

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

registered already but showing need to register to submit

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

queue?

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

I submitted a source code before they changed N and T, and got WA for no reason, very cool.

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

what's going on. is that really unrated?

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

I don't get it

What was wrong with B?

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

    same here, i also saw the correct constraints after submitting A in 2 minutes(they said constraints were wrong for 10 minutes)

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

Got a round after so many days and that too became unrated :(

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4 years ago, # |
  Vote: I like it +57 Vote: I do not like it

Friday the 13th

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

When I will tell my granchildren that we had rated contests on CodeForces, I bet they wouldn't believe me.

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

After waiting for so many days, we got unrated round... :-(

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

Why unrated? I was really fast in ABC, so sad :/

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

So sad that this is unrated! It's first time I pass the D

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4 years ago, # |
  Vote: I like it +59 Vote: I do not like it

The problems are really good!

It's a pity that so many testers and no one caught the issue with constraints on B :(

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

    What was the issue? I didn't get it !! Were the constraints low or high?

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

      It's too low, so the chance to get RTE is high

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

      I believe the actual constraints were initially 2e5, but displayed as 1000-2000, then midcontest, the constraints were changed, and then again constraints were reverted back with updated TCs.

      Picture with updated constraints

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

    Too many chefs spoils the food

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

    Agree the problems were quite good could have been a great round.

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    4 years ago, # ^ |
      Vote: I like it +30 Vote: I do not like it

    I don't want to say too much, but this isn't the fault of testers.

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      4 years ago, # ^ |
        Vote: I like it +90 Vote: I do not like it

      It is neither author's fault nor testers'. I guess it's contestants' fault that they couldn't guess the correct Constraints.

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        4 years ago, # ^ |
        ← Rev. 2   Vote: I like it +36 Vote: I do not like it

        How about let's try to understand the situation better instead of making pointless sarcastic statements that no one actually implied.

        There are more people involved in contest preparation than just author and tester. Several times accidents have happened because things are changed (and sometimes, need to be changed) at last minute, when most testers have already completed their job.

        And often in real life, taking the blame isn't as easy as "it is person X's fault". There are often cases where something is shitty but no one actually really did anything wrong. Of course something has to change but it isn't as simple.

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

          Okay, sorry for that but if things are changed at the last minute, then it is better is postpone the contest and have it tested again. It's better for everyone.

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

          don't get me wrong but if the above comment was by Monogon you must have laughed and upvoted too.

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

      Maybe they don't even know if the constraints are right or not, so it is not appropriate to put the responsibility on the testers without thinking about it, I think.

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

You know . when you make round unrated half of participants are happy and half not !. im in unhappy group . also when the reason of that is just a bit change in limits!!!!

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

when u finally get <2k rank but round becomes unrated :(

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

Luckily I didn't use array with constant space in B

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4 years ago, # |
  Vote: I like it +78 Vote: I do not like it

40 testers and noone used assert while testing to check the constraints??? Seriously what did all these testers do? Felling sad for the authors :(

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    4 years ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    Don't you know, testers job is to ask for contributions?

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

      Actually, testers could not get any contribution.

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    4 years ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    It's writer's job to add validator and validator tests. And coordinator's job to check if the author did it.

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

      I know, I was involved in preparing and testing many contests (Not Codeforces rounds). Usually while testing assert should added every where, to check the constraints and all other conditions.

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

Very disappointing. 3 questions inside 25 mins and on track for CM status, and then it's unrated because the constraints were wrong.

I sympathise with the writers and am grateful for the effort that is put in. How did the testers not pick this up?

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

What was the mistake(in constraints) in B ?

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

    The correct constraint is $$$2 \leq n \leq 1000$$$, but at the beginning of the contest it was $$$2 \leq n \leq 2 \times 10^5$$$. Now the constraints have been fixed.

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

      I think it is the other way. The tests where with arrays of size up to 2e5, but the statement stated n<=1000. Then they changed the statement, then the tests, then the statement again to be like it first was.

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

I am not sure what the testers are supposed to do but confirming the constraints seems like one of the first things to do. Anyways, the problems were nice. Also, I think there should be a gap between different tests in sample. Makes it a lot easier to read.

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4 years ago, # |
← Rev. 3   Vote: I like it -30 Vote: I do not like it

.

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

It's a shame the round is unrated, the problems are quite beautiful. The issue with constraints on B was not the fault of authors, so please don't downvote the blog out of anger.

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    4 years ago, # ^ |
      Vote: I like it -52 Vote: I do not like it

    ok,We will downvote your comments from now on

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      4 years ago, # ^ |
        Vote: I like it +79 Vote: I do not like it

      Downvote me for being supportive of the setters who had nothing to do with the cause of it being unrated? Okay, then I'm proud of those downvotes

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

        Ok I had some slightly bad information at the time I made my comment, but I still stand that people shouldn't downvote the announcement or comments before understanding how the error happened. Still just wait for an explanation of what went wrong.

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

      I don't think it's a wise move ...

      I know you're angry for the contest, yes, we are all disappointed, but no matter how the contest is, it's not the fault of these users who write their comment, I think. So it may be a better choice to delete what you say just now.

      No offense to anyone.

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

Feeling Sad for SleepyShashwat !!! Problem set were really good !!

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

(IMG_20201113_213202.jpg)

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4 years ago, # |
  Vote: I like it -6 Vote: I do not like it

This is the first time i solved a problem with in 60 seconds i got 500 points but sadly the contest became unrated :(

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

Even though it's unrated, don't discuss the problems, please, before the end of the contest. Writer is still going to give prizes

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

One request to codeforces if round is unrated please use bold letters so we don't get a blow after a while

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

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4 years ago, # |
← Rev. 2   Vote: I like it +81 Vote: I do not like it

[Deleted]

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

B positive

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

The tasks were really very interesting.

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

When you solve 3 problems in 12 mins finally, after consecutive blows in previous contests, and the entire universe conspires to screw your rating!

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

Damn I couldn't get C but solved D and climbed to rank 18 for a moment. And now I am like bruh

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

Actually,B doesn't really need an array.

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

Thank you. I love Codeforces!

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

If you got the idea of problem B, it didn't matter the constraints. And the notification of the correction was done with plenty of time to review the problem for any player. I don't think the effect to the score would be stronger than what happens when hidden tests fail at the end of the round after pretests passed. In my opinion, the round shouldn't be unrated...

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

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4 years ago, # |
  Vote: I like it -12 Vote: I do not like it

came to read comment section just to be sure that It's unrated.

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

I was supposed to lose 73 points... and then the round became unrated.

Anyways, I still think it's a pity that the round is unrated because problem B was nice (even though I couldn't solve it). Based on comments, the remaining problems were also nice.

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

well i think i found solution to C but its way too hard for C and takes too long to code ... D was really easy for me on the other hand maybe im a potato :/

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

    C is easy: You just have to make the parity of a[i][j] the same as i + j.

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

    Well, you could make some elements even, and some elements odd. After actions your matrix mod 2 should look like:

    0 1 0 1
1 0 1 0
0 1 0 1
1 0 1 0

    So the algorithm is:

    if ((i % 2) + (j % 2) % 2 && a[i][j] % 2) a[i][j]++;
else if ((i % 2) + (j % 2) % 2 == 0 && a[i][j] % 2 == 0) a[i][j]++;
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4 years ago, # |
  Vote: I like it +4 Vote: I do not like it

Today maybe it was my best performance , and it got unrated .In the next contest it will be rated and I will get a minus 50. Cause that's life.

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

    But it'll not change the fact that it is your best performance today isnt. Don't put a number tag on everything , life will be beautiful.

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

what is wrong with this idea for $$$D -$$$ If n is odd $$$or$$$ (n is even and there is no odd frequency element) then $$$YES$$$ else $$$NO$$$

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

    If all elements xor =0, then n is even will still be possible

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

    It should be : if n is odd or (n is even and the xor of all the elements is 0) then Yes else No !

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

    Try this testcase: 4

    4 1 7 2 Answer is: YES

    1

    1 2 3 because: 4 XOR 1 XOR 7 = 2

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

What is wrong with my code(problem D) https://codeforces.net/contest/1438/submission/98320619

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

Dear division 1, the short interaction between you and me was nice. Now, we have to part away.

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

.

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

    for each i and j, ensure that inp[i][j] + i + j is even (or odd). then adjacent numbers will have opposite parity, making sure that adjacent numbers are different.

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

    Try to arrange elements like , 

    0101010
1010101
0101010

    where 0 represent an even number and 1 represent an odd number. Of course you can always change the parity of a number by adding 1 to it.

    I have seen that most of the people have done it by using dfs also.

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

Well it was Friday the 13th. Coincidence? I think not :)

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

Can someone explain how to solve problem C?

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4 years ago, # |
← Rev. 2   Vote: I like it +76 Vote: I do not like it

3blue1brown styled Video Editorials:

Problems A+B: https://www.youtube.com/watch?v=Z0JKnlmhVOc

Problem C: https://www.youtube.com/watch?v=A3GVI-nxjLM

Problem D: https://www.youtube.com/watch?v=e1TylJJr6Bw

Problem E: https://www.youtube.com/watch?v=wR_qg1XwAg0

Problem F: https://www.youtube.com/watch?v=KC6S5txBsdE

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

    Awesome explainations man! I really hope you continue doing them for other rounds.

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

    looks like i supercomplicated B and C. :(

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    4 years ago, # ^ |
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    Really nice and quick realisation! Do you have a public repo where the code for the videos is published?

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

did you also overcomplicated solution for B or are you normal?

expected solution was if all elements are distict print "NO" else "YES".

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

So in D, I constructed solution for odd n and couldn't get the x-or = 0 thing for even n, foolishness 100. Just got it now.

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    4 years ago, # ^ |
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    for n-odd i think the solution is xor between all numbers and that's all. So you just have to print 1,2,3 1,4,5 .. 1,n-1,n for n-even i think you don't have solution if : all numbers have the same bit 1 or xor between all isn't 0. WA on test 4

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    4 years ago, # ^ |
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    Same thing.

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4 years ago, # |
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Did anyone else use 2-SAT for C? xD

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    4 years ago, # ^ |
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    twf using dfs for C

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      4 years ago, # ^ |
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      Pfft, you aren't a real programmer if you don't solve 2-SAT by putting it into your own hyper-optimized (exponential but still super fast) 400-row general SAT solver.

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4 years ago, # |
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Nobody did any hacking, interesting XD

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4 years ago, # |
  Vote: I like it +56 Vote: I do not like it

It's okay that the round is unrated. It happens.

However, I hope the announcement would emphasize the fact that it's unrated when it's unrated. I saw only the first two sentences of the announcement, and I didn't read the rest of it because I saw that it was talking about problem B and I already passed it, so I thought there is no need for me to read it any further.

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    4 years ago, # ^ |
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    Exactly. I just now came to know that the round is unrated :(

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

Can anyone explain why my dfs solution for C is giving wrong answer on pretest-2 here's my Submission.

I've tried it on some other test cases and unable to find any mistake. Can anyone help?

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    4 years ago, # ^ |
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    Spoiler

    Basically, it's possible for your code to increment the same value twice.

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4 years ago, # |
← Rev. 5   Vote: I like it +34 Vote: I do not like it

My solutions:

A
B
C
D
F
E
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4 years ago, # |
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Video Editorials https://www.youtube.com/watch?v=RXJOWUEQz7k

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

Finally 13 th November. It's Unrated,still intrigued with some great problems....

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4 years ago, # |
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Can anyone please tell me as to why this solution to B was wrong?

Link to Submission
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    4 years ago, # ^ |
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    Try this testcase

    1

    5

    2 2 2 2 2

    Your programme will not take all of the inputs.

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4 years ago, # |
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Never keep a contest on Friday the 13th

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4 years ago, # |
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Is it unrated now?

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4 years ago, # |
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Video Editorials https://www.youtube.com/watch?v=xxAr1ytqWhs

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4 years ago, # |
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We want one more rated contest in this week as this contest became unrated

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4 years ago, # |
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Why this solution doesn't work 98303387, but this solution works 98327745?

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    4 years ago, # ^ |
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    Because in the first one when i=n-1, a[i+1] is out of bounds.

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4 years ago, # |
← Rev. 3   Vote: I like it +11 Vote: I do not like it

Important test case is missing from D. I submitted what should be an incorrect solution, and later resubmitted a correct solution. However, my incorrect solution also passes.

The test case in question is where N = 4 and the answer is YES, e.g. N = 4, A = 2 2 2 2, or N = 4, A = 1 1 3 3

My incorrect code printed out "N-4" as the the number of steps, which gives an output: steps = 0, ops = 1 2 3

Clearly this is incorrect, and I corrected my code to output: steps = 1, ops = 1 2 3

However the test cases are not currently sufficient to identify this bug.

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    4 years ago, # ^ |
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    I think it's checker's job to check the correctness of your output

    The checker reads the number of steps. Because it's 0, the checker doesn't read any operations and your output is correct. CMIIW

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      4 years ago, # ^ |
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      0 would be an incorrect number of steps in the case N = 4, A = 1 1 3 3

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        4 years ago, # ^ |
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        Yeah you're right, I didn't test your program with the last input

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4 years ago, # |
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some please point the mistake in this Problem C solution solution_link

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4 years ago, # |
← Rev. 2   Vote: I like it +1 Vote: I do not like it

Easy solution to problem E:

Notice that if $$$a_l \oplus a_r = a_{l+1} + a_{l+2} + ... + a_{r-2} + a_{r-1}$$$ is satisfied, then $$$a_l + a_r \geq a_{l+1} + a_{l+2} + ... + a_{r-2} + a_{r-1}$$$ is also satisfied.

Assume we fix the position of the rightmost element $$$r$$$. Now let $$$l$$$ be the index of the first element to the left of $$$r$$$, so that $$$a_l + a_r \geq a_{l+1} + a_{l+2} + ... + a_{r-2} + a_{r-1}$$$. The sum of $$$a_l ... a_r$$$ is at least twice as large as the sum of $$$a_{l+1}...a_{r-1}$$$. Lets denote the sum $$$a_{l+1}...a_{r-1}$$$ by $$$x$$$. Notice that the element at the next valid left endpoint will have to be at least $$$x * 2$$$, the next one at least $$$x * 4$$$ ... Hence there are at most $$$log(maxA)$$$ candidate left endpoints for a single $$$r$$$. We can check all of these subarrays $$$O(N \cdot logN \cdot log(maxA))$$$ time using range queries or set (the solution works with a very small constant factor).

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4 years ago, # |
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Hello, a newcomer here.

I was trying to use pypy3 to do F, and I got a lot of TLE's. I tried many ways to go around this, but I wasn't able to find a not-very-dodgy solution: I had to do it in "batches"

https://codeforces.net/contest/1438/submission/98332683

Is there a not-very-dodgy way to do this with pypy?

Here are some of my failed attempts: https://codeforces.net/contest/1438/submission/98331404 https://codeforces.net/contest/1438/submission/98330796

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    4 years ago, # ^ |
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    I agree with this. I can't find a way to fit the solution within the time limits using pypy either.

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4 years ago, # |
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can anyone explain code from jiangly

    int t;
    std::cin >> t;
    while (t--) {
        int n, m;
        std::cin >> n >> m;
        for (int i = 1; i <= n; ++i) {
            for (int j = 1; j <= m; ++j) {
                int a;
                std::cin >> a;
                std::cout << a + (a % 2 != (i + j) % 2) << " \n"[j == m];
            }
        }
    }

// Plz explain this line
//  std::cout << a + (a % 2 != (i + j) % 2) << " \n"[j == m];


Thank you folks.
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    4 years ago, # ^ |
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    If (a % 2 != (i + j) % 2) this statement is true it will add 1 with a . And the statement means -->> a odd and (i+j) even -OR- a even and (i+j) odd.

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      4 years ago, # ^ |
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      how does this syntax works << " \n"[j == m]; ?

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        4 years ago, # ^ |
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        That's the equivalent of saying:

        if (j == m) cout << '\n';

        EDIT: Think of it this way:

        You are given a string of two characters ' ' and '\n', which is represented as " \n". Take the character at index [j == m]. Keep in mind that j == m yields either 1 (true) or 0 (false).

        Hope it clears it up.

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        4 years ago, # ^ |
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        if j==m it will print a new line otherwise a space

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4 years ago, # |
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upvote this comment if you too think today's contest was mainly based on simple observations only.

[please don't downvote to pull my leg]

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    4 years ago, # ^ |
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    That's the case with most Div2 rounds nowadays, which is by no means a bad thing. In fact it's only true with A, B and C problems. Give D, E and F a go and you'll be proven wrong very easily. People of all levels get 1 problem to play with, while others stay far below/above their current level and in my opinion that is very well balanced.

    Problem solving is all about logical thinking and making observations, maths and algorithms are really the tools to execute the idea.

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