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MagentaCobra's blog

Codeforces Round #655 (Div. 2)
By MagentaCobra, 4 years ago, In English

Hey everybody!

We (MagentaCobra, Tlatoani, golions, qlf9) are super excited to invite you to take part in Codeforces Round 655 (Div. 2), which will happen on Jul/11/2020 18:05 (Moscow time). Please note the unusual start time. The round is rated for users with rating strictly less than 2100, although higher rated users are more than welcome to take part out of competition.

Huge thanks to those who helped make this round possible:

There will be 6 problems and 2 hours to solve them.

We really hope you enjoy our first contest!

UPD: Scoring Distribution:

500—1000—1500—2000—2500—3000

UPD: Due to long queue, the round will be unrated. We're extremely sorry this happened, and all of us are sad about it. We hope you will at least enjoy the problems.

UPD: Editorial

  • Vote: I like it
  • +1346
  • Vote: I do not like it

Comments Comments (319)
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4 years ago, # |
  Vote: I like it +8 Vote: I do not like it

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

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    4 years ago, # ^ |
      Vote: I like it -27 Vote: I do not like it

    No score distributions until now?

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

      Once score distribution was published 2/3 hours before.but its 32 hours more left why are you hurrying!

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      4 years ago, # ^ |
        Vote: I like it +19 Vote: I do not like it

      What do you even use score distributions for? Is there some op preparing/strategy based on score distribution I am unaware of?

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

        Well usually people go from the easiest to the hardest. But for example if both E and F have the same score, you might want to read both of them first and then decide which one to solve.

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

          What order to read problems can be decided right before the round starts. You don't need to know 32 hours in advance

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            4 years ago, # ^ |
              Vote: I like it +53 Vote: I do not like it

            That's true I suppose. I was just answering the question of why you even need to know the scores.

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

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

      Feel sorry for people who got their best rank in this contest (like me). Sob :(

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4 years ago, # |
  Vote: I like it +194 Vote: I do not like it

Hope you all enjoy the problems :)

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4 years ago, # |
  Vote: I like it +97 Vote: I do not like it

xD how much problems did he rejected :)

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4 years ago, # |
  Vote: I like it +96 Vote: I do not like it

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

Hoping to see good and interesting problems rather than only maths

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4 years ago, # |
  Vote: I like it +169 Vote: I do not like it

.

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    4 years ago, # ^ |
      Vote: I like it +54 Vote: I do not like it

    I think you shouldn't put memes in a language other than English or Russian, many of us don't understand it.

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

      You mean: "I think you shouldn't put memes"?

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      4 years ago, # ^ |
        Vote: I like it +81 Vote: I do not like it

      Or maybe only in English,many of us don't understand Russian too.

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        4 years ago, # ^ |
          Vote: I like it -63 Vote: I do not like it

        No offense, but do you think it is decent to say that in a website maintained by a Russian university? Why "should" Russian users spend time translating their memes to let you understand?

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

          This is not about wasting time, I mean memes are for fun... if someone is spending his time in making it then it's better if everyone understand it.

          P.s: I don't think Russian gets a special power if this website is maintained by Russian university.

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      4 years ago, # ^ |
        Vote: I like it +19 Vote: I do not like it

      It is saying " Rating double in 25 days "

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

You forgot to mention that score distribution will be updated later

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4 years ago, # |
← Rev. 2   Vote: I like it +121 Vote: I do not like it

I hope C and D will not be too easy. Bring back the glory of div2C.

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

Hoping to see myself in Cyan after this round.

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4 years ago, # |
← Rev. 2   Vote: I like it -80 Vote: I do not like it

I have to miss a Div.4 round for this :(

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4 years ago, # |
← Rev. 2   Vote: I like it -30 Vote: I do not like it

[Deleted]

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4 years ago, # |
  Vote: I like it -76 Vote: I do not like it

Hope to become LGM this contest!

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

Why there is no "as a tester" comments until now ??

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

Waiting for this contest, Contest in a gap of seven days (Global Round 9 was on the 4th of July). Excited Can't-Wait!

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

Wow! This seems like a really good contest!!!!! Out of curiosity, is there any advice you would give a new and inexperienced :P coder? In particular, I am very interested in what qlf9 has to say.

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4 years ago, # |
  Vote: I like it +28 Vote: I do not like it

Interesting to see four author from four different country. Finally a round which will not called some countryan round.

I am little bit curious to know how you four people from four different country get together to prepare the round?

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

    I think they studied in the same school, although I'm not sure

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

one day CODEFORCES will renamed to MONGONFORCES

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

Where are the tester comments, how will I know if the problems are interesting :P

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4 years ago, # |
  Vote: I like it +2 Vote: I do not like it

i hope that the statement of Problems be to short like Announcement :XD

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

Long time no see :v

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4 years ago, # |
  Vote: I like it -26 Vote: I do not like it

I hope we all will get maximum increase in rating in the first contest of MagentaCobra

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

Hope to have negative rating after this contest.

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

    And Surely you can do it ..I checked your profile,, you just use this id for doing this :D

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4 years ago, # |
  Vote: I like it +138 Vote: I do not like it

so many unnecessary blog in recent action !!

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

    Hard work & up your rank

    Create a meme to increase your contribution

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

Our college decided to dump on us every deadline of submission between 8th-10 July and I still can't believe how well it fit in the long gap between after back-to-back rounds!

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4 years ago, # |
  Vote: I like it -25 Vote: I do not like it

Please upload the scoring/weightage distribution of the problems

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4 years ago, # |
← Rev. 5   Vote: I like it +19 Vote: I do not like it

Me watching more and more contests coming after each other!

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4 years ago, # |
← Rev. 2   Vote: I like it +72 Vote: I do not like it

[Your text to link here...](

)
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    4 years ago, # ^ |
    ← Rev. 5   Vote: I like it -14 Vote: I do not like it

    Sorry for the meme :( I just replied his comment :(

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

      Now the meme is true AF.that man is also like 655 div -2 who can't help mr bean!!

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4 years ago, # |
← Rev. 4   Vote: I like it -20 Vote: I do not like it

Every time I read comments .There are lots of memes and some of these are motivating to take part in round .

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

my first contest need some suggestions??

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4 years ago, # |
  Vote: I like it +169 Vote: I do not like it

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

I hope to become expert in this round :)

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4 years ago, # |
  Vote: I like it +53 Vote: I do not like it

Go Colonials!

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

    Go wassim.omais!

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

    I believe we should cancel the term Colonials. It honors our Founding Fathers, which were some of the most racist men in history. #CancelTJHSST.

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      4 years ago, # ^ |
      ← Rev. 2   Vote: I like it -6 Vote: I do not like it

      I agree. The multitude of racists among the Founding Fathers is unacceptable. Anyone who says otherwise is privileged and racist. #CancelTJHSST

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

        AkshajK I agree with 0_IQ_DOG. Take down your racist comment. Don't be complicit in honoring those terrible men. Let's get TJ renamed to Northern Virginian School!

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

      Founding fathers were colonials, hitler was human should we cancel the term human?

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

        yes... after all, I am an ogre, so I would be obliged to endorse such a cancellation.

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

        i am simply a zombie, so such a cancellation works fine for me.

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

Hope there will be interesting problems. Good luck and High rating.

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

ummm what is meant by cyan etc etc. i am new here and don't know much about the slangs used here !!

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

is your score the same as your rating? i'm new to this website so idk how it works :/

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

    No,you will be given a rank based on your total score and your rating will increase if you performed better in comparison to the rating you already have.It is not like if you have earned total 2000 points then your rating will become 2000 !!

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4 years ago, # |
← Rev. 2   Vote: I like it -49 Vote: I do not like it

![ ](meme.jpg)

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

    When you want something, all the universe conspires in helping you to achieve it. 

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

    Thanks for your support guys! I am overwhelmed.

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

A few days ago, my contribution was +1, now it's 0, how to keep or rise my contribution?

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

    Keep constant by no comment/write blog And rise/decrease contribution by comment/write blog according to your get upvotes/downvotes...

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

    hopefully now it's 1 again :D

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

Unusual start time nowadays have become the new usual start time.

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

wow! the one who is no.2 contributor is coordinating this round!!! I think we will get problems that we will enjoy to the fullest

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

Hi I am a beginner.I want to ask that at least how many questions one should solve in a Div2 contest to avoid rating decrement.

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

    In your rating range two problems.. I guess even if you solve just 1 but fast.

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

    Looking at your current rating two questions should definitely do the job and sometimes, if the second question is little bit tough then solve the first question quickly to avoid rating decrement.

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

24k+ participants already!

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

Isn't the queue very long?

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

why does printing odd numbers in first problem throw a wrong answer??

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

over 75 pages of submissions in queue...

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

that's all(

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

waiting for hundreds of "queue forces" commentaries :)

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4 years ago, # |
  Vote: I like it +45 Vote: I do not like it

Waiting and Waiting..Really Annoying !!!

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

Can we have this contest unrated, please?

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

Yet Another Queue Problem

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

(i am crying): what is going on codeforces?((

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

i submit problem number B 10minutes ago..it's still in queue

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

I think this round will unrated!!!

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

After a week of waiting...

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

More Than 125 page of queue

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

my code had been in queue for 15 minutes, I think this round will be unrated

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

10 minute queue is definitely not reasonable and round should be unrated..

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

168 pages of queue :(

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

already 15 mins now still in queue

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4 years ago, # |
← Rev. 2   Vote: I like it +31 Vote: I do not like it

I don't want to look like I am overreacting, but I think that most of the beauty of CF rounds comes from the instant feedback and, as you can notice, this rounds has a big lack of such feature. Therefore, in my opinion, this round should become unrated.

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

Shoot,I had been waiting for about 10 minutes to get WA on test 1

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

Is it gonna be unrated ?

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

I was waiting for this contest since 1 week but such queuing issue is really annoying

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

Okay, I give up! It would be ridiculous if this round is rated!

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

QUEUEFORCES

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

Welcome to Queueforces

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

QueueForces

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4 years ago, # |
  Vote: I like it +125 Vote: I do not like it

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4 years ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

The questions are really interesting but the long Queue ruined the contest.

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

submit a solution and then refresh and refresh for 15 minutes+ to see that solution passed or not or even Wa on test 1..What the hell -_-

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

The contest should be unrated.

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

As per the announcement, contest should go unrated if the queue goes for more than 15 minutes, right? I could see that it is 20 minutes long right now. So, is it going to be unrated?

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

20 minutes and still in the queue..

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

Right now the queue is 16 minutes+. Disappointing.

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4 years ago, # |
  Vote: I like it +184 Vote: I do not like it

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

Will it be unrated?

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

Queueforces again :(

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

Queue reached 15min. Is it rated? NO! It's unrated!

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

YEEEEAAAAH ... round unrated !!

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

It is sad that round is unrated. btw Problems were interesting.

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

Im supposed to be pupil in this round. Sad

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4 years ago, # |
  Vote: I like it +2 Vote: I do not like it

Queues Again Came Up , I again fear Monogons Next Round!

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

Sorry, because of the long queue the round is unrated.

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

Was literally doing good in this one, btw nice questions

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

Testcases were weak for C and moreover announcement for A actually gave out the answer.

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

    How to solve C

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

      Contest might be unrated ,but still it is running.Ask your question related to answers after the contest.

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

        I guess it's better to solve problems after contest else one has to wait 25+ min just to get verdict

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

    Just curious, what wrong idea was able to pass due to the weak pretests of C?

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

      9
      3 1 2 6 4 5 9 7 8
      For this test case answer is 1. In my code I had the condition when the max element till now becomes equal to the index, I was incrementing my answer by 1 or 2. My code will print 3 for the test case mentioned and it passed the pretests.

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

      I forgot about test when "unsorted" part is in the middle

      Like this

      Really stupid that their didn't make $$$t \leq 1000$$$ and made second case all permutation of 6... It is really easy to generate and I think that would reduce number of failed codes from 600 to around 20...

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

Great! waited a week to participate and then it's become an unrated round

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

    It's like going to Pierre's on Wednesdays

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

Hope we won't have the same issue in tomorrow's contest.

BePositive

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

Very interesting tasks and once again unrated.

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

It's sad that contests with nice problems are getting unrated. First Monogon's round, now this.

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

To be honest, I feel bad for the authors.

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

Today hackerearth and codeforces became the same :)

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

    hackerearth is way behind in terms of problem quality

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

Problemset was quite intersting, yet unrated. :3

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4 years ago, # |
  Vote: I like it +2 Vote: I do not like it

I have really enjoyed your problems! I hope to see you in the next rounds as writers :=)

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4 years ago, # |
  Vote: I like it +37 Vote: I do not like it

No need to apologize MikeMirzayanov. You have been doing an awesome job. We are proud to have you.

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

Nice contest after long long time, but it's unrated :(

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

One hour before contest

Me: Well, good rating to me, contest after a long time.

Goes to contest page to register

Me: Oh look, there are so many upcoming contests!

Monogon contest name stands out

Me: Lol, when Monogon made a contest the last time, contests this close were plagued with Queueforces. Let's hope it doesn't happen this time.

Submit B, redirects to status page

Gives up CP and becomes a soothsayer's apprentice...

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    4 years ago, # ^ |
      Vote: I like it +25 Vote: I do not like it

    The queue strikes back.

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

      “Mike Awakens”.

      Becomes the “Last to Shuteye”.

      Leads to the “Rise of the Sleepcoder”.

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

I thought cf has overcome it queue problem. Last few contests were very nice. Pretests were judged very fast and they were very strong too. Sad about today's contest. Hope things will be fine soon.

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

In C, is it true that you can sort any permutation in 2 or less actions?

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4 years ago, # |
  Vote: I like it +178 Vote: I do not like it

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

    Please translate. D:

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      4 years ago, # ^ |
        Vote: I like it +19 Vote: I do not like it

      You submit the solution, but verdict will be given to your grandson Xd

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

      There is this famous TV comedy show in India. In that show during a festival sale, this character who worked in a shop as assistant gave the idea of the offer to shopkeeper-"Let people buy items, we will take money from their grandsons." This meme is based on that line "You solve the question, verdict will be given to your grandsons"!.

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

Just Want to ask one question to problem setter why you used name Omkar ?

At the start of the contest I was like, Did I made any mistake? ...xD

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

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

When you finally think you gonna reach expert but god has other plans.

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4 years ago, # |
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The queue is ruining the experience...

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

To be honest, I feel bad for the authors. Problem were pretty interesting

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

Why cant the difficulty of A,B,C be increased so there are lesser number of submissions? and i don't think there's much one can learn from the current A B C problems anyways.

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

    maverick16 thats why there is a div1 too. I think the problems were very interesting.

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4 years ago, # |
  Vote: I like it +108 Vote: I do not like it

Mike after making changes to the platform:
PS: this is just a meme and I really respect what Mike is doing for the cp community

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

Guys, I am disheartened a lot. I started CP just 3 months ago. I was a noob. Today, before the round becoming unrated my rank was 1260. Delta was +206. It is very rare. I have lost the confidence. What positives should I take from this?

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    4 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    If you have the ability to go +206 this round, you will be able to do so again in future rounds. Just keep practicing and know that you're improving!

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

      The artwork in ur dp seems really cool; can you tell me the source?

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

    same about me. Delta was +238, though it would be lower, had everyone done the problems with usual speed. I suggest you not to worry since in the long run, such things won't matter much. If you really improved your skills, you will get that rating in the next contests.

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

    negative contribution!! XD
    u can do good in the next round too, i was also getting enough delta to be in div 1 :)

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

How many servers are running cf?

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

I am feeling bad for the problem setters.

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4 years ago, # |
← Rev. 3   Vote: I like it -29 Vote: I do not like it

Good contest and awesome problems.

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

I saw somewhere that this is the first contest organised by its organisers. But it seems after looking at the questions that organisers have large experience. So much beautifull,difficult questions i have never seen in any single contest

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

:)

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

Cool problems, pity the que blew out of proportion.

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4 years ago, # |
  Vote: I like it +145 Vote: I do not like it

Nowadays, Codeforces has become Constructive forces, Missing those days when we were able to find good concepts like binary search, DP, Graph, DSU, etc in problems.

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

    In the past, C, D problems really made me comfortable even when I could not solve them. These days, I feel like C, D problems are usually just some random observations with under 10 lines of code. God, I miss graph problems -_-

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    4 years ago, # ^ |
      Vote: I like it +28 Vote: I do not like it

    Those days are never going to be back, at least not until antontrygubO_o is the coordinator. He rejects 72 problems just to make Codeforces, Atcoder.

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

It seems that we should slightly increase the difficulty of problem A, increase $$$T$$$ for the first problems and make fewer pretests for them.

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

It's bad to see round unrated. I have a suggestion for next rounds . I don't know it is right or wrong.

There may be an unrated easy problem (a+b type) 10 minutes before contest starts, and at that time registrations should be closed. It will help in stress testing. If there will be any problem during testing then round should not be hosted.

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

    Anything could happen during the contest, so I don't think it'll help much.

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

Can anyone help me in C? It's giving TLE

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

    Even though it is unrated, contest is still ongoing. Please don’t discuss the problems.

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

This contest has really good problems and perfectly matches div. 2 status but now it is unrated. let us, Hope, we get some more exciting contests like this one.

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

I think one should go through this article and understand difference between programming and coding.Programming vs Coding.These cleared many of my doubts between Coding and Programming.

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

The contest was really awesome, hope to see more from you! :)

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

[Sorry for the meme. But really disappointed , i missed a important task for attending this]

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

Nice Contest! I really liked the problems!

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

How to solve D? Thanks in advnce:)

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

    You can choose at most (n+1)/2 elements, and you should choose (n+1)/2 elements because all elements are non-negative. And you can observe that unchosen elements cannot be adjacent.

    Then the problem is find n/2 elements which are not adjacent and have smallest sum. DP can solve it. The time complexity is O(n).

    I think I am right.

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      4 years ago, # ^ |
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      I also thought of the same approach but couldn't figure out which n/2 elements to eliminate from the sum.Could you help a little more on how to do the dp part?

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

        86561722 You can refer to my code. Notice that head and tail can not be chosen simultaneously.

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

          yeye Is it not possible that n/2 elements which contribute to smallest sum, change after one operation(for instance, after smallest element is replaced by sum of its adjacent elements in the very first operation).

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            4 years ago, # ^ |
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            Can you give an example? My submission has been accepted.

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            4 years ago, # ^ |
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            I see. This approach is global. No need to worry such things.

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

How to approach question D?

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

    there is a simpler solution. firstly note that we cant have three consecutive elements in a sum. also we can't have two consecutive elements which are not in the sum. also note that we can only have at most (n+1)/2 elements in the sum. so we can simply find the max over the sum of all (n+1)/2 alternating sequences

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    4 years ago, # ^ |
      Vote: I like it -7 Vote: I do not like it

    Though I haven't implemented it , but may be this greedy works. Always try replacing those adjacent is who have maximum value of ai+1 +ai-1-ai. Idk if this works or not.

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

      I think it doesn't work. Try: 1 2 3 3 2. The answer is 7, but your algorithm (if I got it right) gives 6.

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        4 years ago, # ^ |
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        I think it gives 7 replace 1 3 array becomes 4 3 2 Repalce 4 3 array becomes 7.

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

          This doesn't match your requirement of "maximum value". Your replacement gives: 3 + 1 — 2 = 2. But if you replace the 4 1 array (remember the array is circular) you get: 2 + 2 — 1 = 3, which is higher.

          If the circularity of the array confused you, let's rotate it: 2 1 2 3 3.

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            4 years ago, # ^ |
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            Yep Sorry! thus greedy fails for this problem. Only way is to consider all the possible cases through dp.. Thank you for figuring my mistake.

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

Can someone please help me with approach of B. It's giving TLE in pretests 4

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

    Simply check for each factor.

    Time Complexity O(sqrt(n))

    Code

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      4 years ago, # ^ |
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      Thanks a lot! It was quite easy. I don't know why I couldn't crack it!

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

    Its simple for as we can see for even n ans is n/2, n/2 and for odd n if n is prime then ans is 1, n-1 it is self explanatory. now if n is odd and it is not prime then find smallest prime divisor of n let it is sm(n) so ans is n/(sm(n)), sm(n) it is optimal solution

    to find smallest prime divisor refer this

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

That's completely unfair !!. been for a long time doing bad in contests and when i don't, it's going to be unrated. i am very disappointed.

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

Waited for 10 minutes for the verdict Wrong answer on pretest 3.

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4 years ago, # |
← Rev. 2   Vote: I like it +9 Vote: I do not like it

Very beautiful problems; great round! Irrespective of this round being unrated, I enjoyed the problems a lot, so thanks problem-setters!

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4 years ago, # |
← Rev. 2   Vote: I like it +3 Vote: I do not like it

Nice problems

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

Would appreciate any help in figuring out the issue with my C submission:

http://codeforces.net/contest/1372/submission/86577996

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

    You can change 1 3 2 4 ---> 1 2 3 4 in 1 operation

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    4 years ago, # ^ |
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    If all elements that are out of place form a single subarray, it's also solvable with 1 operation, e.g. 1 2 6 5 4 3 7

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      4 years ago, # ^ |
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      Yeah I forgot to consider this. Thanks

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

Thanks for such a hard competition that must have shown everyone like me that you need more practice. After giving this contest i feels that i started coding yesterday only :(

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

For question C,i counted number of sets where a[i]=/=i for example if a = {5,4,3,2,1} {5,4} and {2,1} are two such sets so ans = 2, for a ={3 2 4 5 1 6 7} {3},{4,5,1} are two such sets so ans = 2.I failed on pretest 3.Can anyone provide a counter where it may fail.

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

    Try for a = {3,2,5,4,1} , ans is 2. {3,2,5,4,1} -> {4,1,2,3,5} -> {1,2,3,4,5}

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    4 years ago, # ^ |
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    look bro maximum answer will never exceed 2 ,according to your technique it will exceed 2. for a={3 2 5 4 6 1 7} {3},{5},{6,1} will become three sets but answer should be 2. in 1st step:-{3 2 5 4 6 1 7}->{5 4 6 2 1 3 7}(taking from position 1 to 6 as sub array) in 2nd step:-{5 4 6 2 1 3 7}->{1 2 3 4 5 6 7}(taking from position 1 to 6 as sub array ) so, the basic point is if number of sets is more than 1 answer will be 2 always Hope u understood..

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

How to solve D ?? looked like dp to me.

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4 years ago, # |
← Rev. 2   Vote: I like it +7 Vote: I do not like it

I found a telegram group with over 2400 participants,in which people were directly sharing problem hints and solutions during live contest.Can something be done for this issue?

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4 years ago, # |
← Rev. 2   Vote: I like it +7 Vote: I do not like it

My solutions for A,B,C,D pending system testing

A) Return all ones

B) The smaller number = A // (smallest prime factor of A)

C) - If already sorted, return 0.

  • If there is only one subarray with all elements unsorted — return 1

  • Otherwise, return 2

D) The task is to select (N+1)//2 elements from the circle such that only a pair of elements are adjacent. Procedure:

  • Rearrange the array by take every alternate element and every other alternate element.

  • Repeat the array once (since it is circular).

  • Take the prefix sum (i.e. cumulative sum).

  • Find the maximum difference of elements (N+1)//2 distance apart.

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    4 years ago, # ^ |
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    What was your intuition behind your solution for D?

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4 years ago, # |
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Problem D: What is the problem with iteratively taking the minimum number of the current set?

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

    How do you choose which one to take if there are multiple minimums? Consider the case 1 1 30 30 20, with answer 61: if you take the first number, you can only get 60.

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      4 years ago, # ^ |
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      Thanks a lot. That completely satisfies my question.

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

      I was puzzled by the same question...Thanks a lot

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

      For multiple minimums occurring together, I choose the one which gives max sum.

      For example, consider 8 4 4 5 9. So, we choose the 4 at index 1 because it gives higher sum i.e. 12 than the 4 at index 2 which gives sum 9.

      What is the problem in doing this?

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

        The big problem is that this algorithm is greedy, just like the one ReginaFelangi described. I believe that no greedy solution exists for problem D because sometimes you might want to “sacrifice” a little bit in one iteration so that you can get much more in the future.

        If you know the structure the correct sequence should have, it's easy to construct a counter-example:

        2 1 1 3  100 90  5
2   4    100 90  5
9        100 90     
190

        Notice how we'd like to keep both 100 and 90, but they are adjacent. This means the correct answer is to keep 2 _ 1 _ 100 90 _, removing the left 1 (sum = 193), but your heuristic says we should remove the right one because (2 + 1) < (1 + 3).

        Another way of looking at it is that you would like to remove 9, but 9 = 4 + 5 = 1 + 3 + 5, i.e. that's actually three numbers from the original array!

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          4 years ago, # ^ |
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          Yeah I understood the problem with greedy. That's why I wrote my next comment but thanks anyways for explaining so well.

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      4 years ago, # ^ |
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      Nevermind. Iteratively taking the minimum is wrong itself.

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4 years ago, # |
  Vote: I like it -7 Vote: I do not like it

Hi guys

try these video solution

Problem C I My self was also shocked how can it be sorted so fast

Problem B Explained Math in detail (Good for math lovers)

Problem A Fastest method but if you have fast fingers :) :)

Hope it help

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

Can someone please let me know why below solution for D doesn't work? Chose the minimum value present currently, replace it by sum of its two adjacent values, do until u r left with only one element.

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

    Can u please tell why can't there be more than 2 special exchanges in C ?

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      4 years ago, # ^ |
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      So below are the possible cases: 1) when array is already sorted then answer will be 0

      2) If lets say starting and last fews elements are in the exact postion we want after getting sorted, then there will be two possible case:

      ->all the elements in the middle portion which we need to sort are in different position as of the final required position then we can sort the complete middle subrray in 1 operation.

      -> If one or more elements in the subarray are in the same position as after it will be in sorted array then we can just select the middle subarray and first distribute all the elements such that no element is in the same position as they will be after sorting, which will require 1 operation, after that we can just use one more operation and sort middle subrray.

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      4 years ago, # ^ |
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      In worst case, you can just select the whole array and make it such that all the elements are in wrong places. After that select the whole array again and sort it. So in worst case, the answer would be 2.

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it +6 Vote: I do not like it

    5

    4 2 1 2 4

    your solution gives 8, optimal is 9

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    4 years ago, # ^ |
    ← Rev. 5   Vote: I like it 0 Vote: I do not like it

    consider this test case : 5 1 3 9 10. your output is 19 but the answer is 20. The optimal answer is always in this form : take a node and from the next node take one and leave one. In this example the first node is 9 and from 10 you will take one and leave one so you will take 9,10,and 1 so the answer is 20. you can simply check all possible cases starting from the first node calculating the current choice's sum using prefix sum on parity, which means that if i is odd then prefixsum[i] is the sum of all odd indices values till i, arr[1]+arr[3] .. + arr[i]. if i is even then it's the opposite, arr[0]+arr[2] .. + arr[i].

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

Hume to apno ne loota gairo me kya dum tha, sala vahi contest unrated hua jisme humara predicted rating maximum tha.

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

D E N I E D

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

After knowing the fact that 72 problems were rejected, I am feeling even worse for the authors

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

[Deleted]

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

-*someone solved A in 1 min*

-I HAD DELTA +228 WHY IS THE ROUND UNRATED

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

Such a beautiful contest with so good questions, but the unfortunate happened. I feel bad for the Setters and testers and for the participants who did better than their average performance today. But still, thanks for this amazing contest, the problems, at least the one I managed to solve, I found then quite interesting. Hope to see more contests like this.

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4 years ago, # |
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In problem B , when n = 63 why answer is 9 54 and not 21 42 ??

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4 years ago, # |
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So much lucky today, :p I would get more than 100 minus ratings in this contest. :)

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    4 years ago, # ^ |
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    Do not worry, you will get it next time, it's fine.

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

I just published a screencast + commentary of getting 13th on my youtube channel, with solution walkthroughs at the end for people who are interested.

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

Question set was amazing. I loved it.

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

Does the problem Ehave a solution with min cost max flow ?

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

delted

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