golions's blog

By golions, 10 days ago, In English

Hello Codeforces!

We, the disciples of Omkar (qlf9, Tlatoani, hu_tao, golions, and Omkar's newest disciple, rabaiBomkarBittalBang), have written our third contest: Codeforces Round #724 (Div. 2)Omkar 3. It will be held on Jun/06/2021 17:35 (Moscow time) and will be rated for users in Division 2 (rating lower than 2100). As usual participants with rating >= 2100 are allowed to compete too, but the contest will be unrated for them.

You will be given 2 hours to solve 6 problems. There may or may not be an interactive problem, so it would behoove you to read the guide for interactive problems. There also may or may not be competitive programming problems, so you should be sure to thoroughly understand everything here.

We would like to thank:

The scoring distribution is 500 — 1000 — 1500 — 2000 — 2250 — 2500.

May Omkar be with you!

Update: Thank you for participating in our contest! The editorial is here. We have video editorials for every problem there!

Update:

The winners in official standings:

  1. xin_chen

  2. adc-s11-sadge

  3. conqueror_of_rainboy

  4. XOXOX

  5. TwTwTwTwT

The winners in unofficial standings:

  1. neal

  2. Maksim1744

  3. dlalswp25

  4. hank55663

  5. fanache99

Congrats!

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

As a tester, Omkar orz!

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    9 days ago, # ^ |
    Rev. 2   Vote: I like it +50 Vote: I do not like it

    The best part is that this roughly translates to Om Namah Shivay because Namah literally means to bow. Omkar orz!

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      8 days ago, # ^ |
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      Does omkar even means shiva? because it means om pronunciation according to me and I verified by searching its meaning

      upd: it doesn't matter. Hoping for good bugaboos and strong pretests.

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    9 days ago, # ^ |
      Vote: I like it +34 Vote: I do not like it

    Why so much reverence to Omkar? I mean I am just curious. You people aren't even Hindus(ig).

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

Hope you all enjoy our problems :)

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

    qlf9 Omkar orz

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

      May Omkar be with you!

      CODEFORCES VERSION:

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

As a tester, I must say problems are really interesting !! All the Best :)

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

    As a participant, I must say please tell me something new.

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

      Meanwhile Negative delta : I am coming to you tonight

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

        After System Testing, "Virtual Contest and Practice Mode" : You could not live with your own failure. Where did that bring you? Back to me!!!

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    9 days ago, # ^ |
    Rev. 2   Vote: I like it -24 Vote: I do not like it

    [Deleted]

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

Interesting problems.

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

everyone click the Omkar 3 link

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

I'm still thinking that you all guys know Hindi ?

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

Very quick scoring announcement!

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

Scoring looks pretty balanced, gonna be a nice round!!!

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9 days ago, # |
Rev. 5   Vote: I like it -32 Vote: I do not like it

When i see there are a lot rounds comming in codeforces :

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

It's time that these posts should use the word "Bugaboo" instead of "problem".

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9 days ago, # |
Rev. 4   Vote: I like it +20 Vote: I do not like it

I was hoping for becoming Expert but now I might get demoted to pupil :(

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9 days ago, # |
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As a best coordinator antontrygubO_o orz!

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9 days ago, # |
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I like this scoring distribution

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

Wow , another contest this week. If codechef could conduct as many contest as they launch new courses for cp then I would have become 4 star on cc xDD.

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

Hail omnipotent Omkar.

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9 days ago, # |
  Vote: I like it +31 Vote: I do not like it
Problem / Bugaboo Names of this Contest
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9 days ago, # |
  Vote: I like it -38 Vote: I do not like it

Brother,just curious to know Omkar means what? The link you provided Omkar3 is youtube link that's the hinduism. From my perspective, Here all contestant are not hindu. But you are spreading your religion by Omkar?

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

    You can just replace omkar with god. This is maybe not for spreading any religion, but instead it creates a humour(here). Also the link is a part of that joke, pointing that its their third contest(its like they created a third part of a kids movie)

    At first it baffled me. But later I recognized that it lightened my mood.

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

    .

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      9 days ago, # ^ |
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      Lmao yep, my real name is Omkar and I’m American :P

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

Why the organisers are obsessed with Omkar. I don't think they even know Hindi.

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9 days ago, # |
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Hope so I will be able to solve B this time

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9 days ago, # |
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Just curious how to become tester

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

    You should be personally familiar with some problem setter, so (s)he could personally kick the s**t out of you if you leak some problems beforehand, spoiling the contest and efforts of many people )

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9 days ago, # |
Rev. 2   Vote: I like it -59 Vote: I do not like it

I love CF

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

I don't have much sense of humour, can someone explain what's going on?

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  Vote: I like it 0 Vote: I do not like it

I like this scoring distribution Scoring looks pretty balanced, gonna be a nice round!!!

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

The good' ol 6 problem 2 hr div2 is back finally!

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"There also may or may not be competitive programming problems" yeah like why would you include competitive programming problems in a competitive programming contest, that would be very weird.

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    9 days ago, # ^ |
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    Yeah they should ask you to create a website :)))

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

Scoring looks encouraging!

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

golions, you made a mistake. This should be BUGABOOS, not Problems.

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9 days ago, # |
Rev. 2   Vote: I like it -38 Vote: I do not like it

God for creating the world and the human race.

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    9 days ago, # ^ |
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    but when did he disrespected other religion,omkar is name of one of the problem setter and I am sure he said it all in sarcastic way

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      8 days ago, # ^ |
      Rev. 3   Vote: I like it -37 Vote: I do not like it

      Omkar for creating the world and the human race.

      That means the problemsetter created the world?

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    8 days ago, # ^ |
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    Ok snowflake

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9 days ago, # |
Rev. 2   Vote: I like it +11 Vote: I do not like it

after looking at a few comments up here, I would like to imagine a Latin American guy named Jesus creating a round, then they put his name on all problems and thanked him in the announcement blog

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    8 days ago, # ^ |
      Vote: I like it -26 Vote: I do not like it

    He wouldn't say that he created the world and human race, right?

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      8 days ago, # ^ |
        Vote: I like it +27 Vote: I do not like it

      lol Everytime someone has prob with other religion,it is always muslim guy from Indian subcontinent,from santa time to omkar name ( although omkar is name of problem setter and he has surely written that in sarcastic way )and even if he hadn't why did you care so much,I know one muslim writer (Dont remember name) has written " all credits due to allah and allah has created world " thing but then no one felt offended lol and then he say " respect all religions"

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

        Should I reply your comment with a fake id?

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

          who say this id is fake?If it was fake I wouldnt have been active daily for the last 6-7 month,Its just that I prefer upsolving instead of giving contest btw You also know I spit a fact so you brought fake id thing in reply

          LET CF BE CODING COMMUNITY DONT MAKE IT SITE TO START WAR ON RELIGION BASIS OR NATIONALITY BASIS ALL CODERS ARE SAME

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

            Do you know about the new feature of codeforces that if you solve any problem it will be showed in your profile. And your profile says that you didn't solve a problem since April, and you total solved 8 problems since you created this fake account!

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

              Great job exposing your own fake account used for cheating in contests.

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                8 days ago, # ^ |
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                lol, that fake account has much higher rank than me! And fake account was created before real account!

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

              Have you even heard of mashup thing,I had done lots of mashup but is this even a point? Point was that you guys had always problem whether it is santa or omkar (although not all muslims, Every community has black spot and I think you are that in Muslims ,cause none of muslims brothers commented except you)

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

      If you want to debate on religion. I'll happy to join you on Twitter. Please let this site be for CP only. It shouldn't matter to anyone if problem setters add one two lines for humour and thanking god according to their own faith.

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9 days ago, # |
Rev. 7   Vote: I like it -85 Vote: I do not like it

.

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

Omkar orz... Om Namah Shivay!

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8 days ago, # |
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Will Omkar inspire the authors to release the Editorial eventually?

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there also may or may not be rated contest so you should read all of the rules about unrated contest.

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  Vote: I like it -38 Vote: I do not like it

God for creating the world and the human race.

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

    you muslims are weird

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

      Muslims say Allah not God. God is a common name of our creator for all kind of people.

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

        lol So he was telling me that I uses fake account, Bro when a muslim author said in a contest announcement blog that allah created universe then why didnt u pointed out?

        Again writing same thing LET CF BE CODING COMMUNITY DONT MAKE IT SITE TO START WAR ON RELIGION BASIS OR NATIONALITY BASIS ALL CODERS ARE SAME

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

        Who decides that God is a a common name. It can be anything... you can't assume it to be God, Allah or whatever... It's ones choice. Also don't get offended by others expressing their beliefs.

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      8 days ago, # ^ |
      Rev. 2   Vote: I like it -11 Vote: I do not like it

      Why is this comment getting upvoted?

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        8 days ago, # ^ |
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        because it's true..ig??

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          8 days ago, # ^ |
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          You don't talk about stuff like race or religion on a cp website.

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      8 days ago, # ^ |
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      From the Indian subcontinent, not from the middle east.

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

What is the Meaning of Omkar ?

The word OM came from Hindu mythology.

OMKAR ओंकार —

OM + KAR = Om is a indeclinable .It is a sacred syllable and is Uttered as a holy exclamation at the beginning and end of a reading of the Vedas or previous to the commencement of a prayer or sacred work.

KAR is from kri कृ root word , which means doing , making , performing.

It is a term, denoting a sound or word which is not inflected.

OMKAR is a SACRED syllable OM itself.

The exclamation OM. It is a Supreme Brahm.

OMKAR is a powerful word when chanting gives physical and mental health. One can feel certain vibrations in the body and so it controls anger, increases patience and tolerance levels.

Chanting of Omkar improves concentration, brings down stress, anxiety, and tension.

It is a meditation. It reduces negativity.

So the meaning of the name has powerful meanings.

I think this will help you.

Sources: What is the meaning of the name Onkar?, What is Meaning of Omkar

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

    I have explained it in short in this comment(see rev 1 of that) https://codeforces.com/blog/entry/91438?#comment-800185 And I don't know why I got a lot of downvotes there.

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

    Yes, True that. Only I would like to add-

    . "Om" is considered to be the cosmic sound. It originates back when nothing existed and space was empty & quiet, the creation of universe brought with itself the vibrations of Om. And hence it was the first sound that ever originated.

    . Proper chanting of "OM" has remedial effects on any mental or physical stress because "om" is considered to be made up of every possible frequencies of sound and when chanted, it tunes with the frequencies of self and provides relief.

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

golions, Is there any way to become disciple of Omkar?

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    8 days ago, # ^ |
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    Do meditation and concentrate solely on the sound "OM" of the universe. Not only will you become a disciple of Omkar, but all your confusion will also go away xD.

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8 days ago, # |
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Good Luck everyone!

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8 days ago, # |
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Hail Omkar

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

When a problem score is 2000, does it mean its difficulty is 2000?

I am new to codeforces. Pardon me.

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

    No, it doesn't. The problem score means only the gap between difficulties of the problems. In average it's close to the truth, but now always :)

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

    No. It is the maximum score you can get upon solving the problem. Difficulty is assigned to a problem after the contest is over, on the basis of ratings of participants who were successfully able to solve it.

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8 days ago, # |
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Seems like problems were made for div1, lol.

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8 days ago, # |
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The Marking system feels shit, if you submit first in just 3 min with one error, gives less marks compared to someone who solved it after 25 minutes.

ughhhh

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

    Wrong submissions have penalties. You should consider checking on more test cases before submitting.

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      8 days ago, # ^ |
        Vote: I like it -24 Vote: I do not like it

      Saying by not even sitting in the contest sounds good.

      Here I am the one who failed horribly in the contest and there you are who didn't attend a single contest giving and firing your utopian quotes on me. :)

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        8 days ago, # ^ |
        Rev. 2   Vote: I like it +5 Vote: I do not like it

        Sorry if that hurt you. I know how it feels dude. I already solved 3 problems with 5 wrong submissions, I already had negative contributions, so I was just afraid to comment with my actual id because of down votes. hehe, LOL!

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

          Yaa, that hurt me, and tell me your real id then ;)

          But, I am feeling sad for you as you care about your contribution more than your rating

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          8 days ago, # ^ |
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          Hey bro finally, I submitted 3 with one wrong submission ;)

          when I was chatting with you at that time I was at one :)

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8 days ago, # |
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I personally wouldn't be surprised if someone said: "Anton did NOT reject problems for this contest!"

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8 days ago, # |
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Was Div2 A always this hard?

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

    nah, i consider this problem to be on div2 b/easy c level

    the fact that problem statement is written so bad makes this problem even harder

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    8 days ago, # ^ |
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    It wasn't that hard especially if you look at the constraints, which made it quite easy to implement.

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The problem statements should rather be considered as riddles.

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8 days ago, # |
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i still don't have Diluc and Fischl..ehe..maybe that's why i still fail to solve their problems

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8 days ago, # |
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There also may or may not be competitive programming problems 

Very true, now my tongue has well-defined six-pack abs after going through these tongue twisters.

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8 days ago, # |
Rev. 2   Vote: I like it +17 Vote: I do not like it

me on A: 31 minutes B: 28 C: 24 I'm not saying it's not balanced but WTF is wrong with me why do I start like an idiot then focus more and more

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    8 days ago, # ^ |
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    supahotfire CM perf orz

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    8 days ago, # ^ |
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    I think A was difficult than usual. I submitted A in 18 minutes still had a decent rank for a while.

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      8 days ago, # ^ |
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      I still dont know why my A is incorrect.

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

        probably because of the 300 size condition

        Edit: Just realized i didn't read the problem properly and thought array may contain any integer

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    8 days ago, # ^ |
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    For me A was harder than B and C. Actually I am not sure if A works. I implemented some brute force for both, A and B, without being able to see if then will TLE or not.

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      8 days ago, # ^ |
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      Edit: nvm it was bullshit

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        8 days ago, # ^ |
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        if there is one negative number the difference will still be positive since we are taking absolute value

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          8 days ago, # ^ |
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          If there's one negative number and a positive one then you will have to infinitely add new numbers

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            8 days ago, # ^ |
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            It seems all of our submission where finaly AC. Congrats to your nice delta!

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        8 days ago, # ^ |
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        Nope, why should it fail??

        If the array is [-a, 0]. Then their absolute diff is still positive (|a|). So it will go on forever. Don't give such heart attacks, I solved with the same logic as you lol.

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      8 days ago, # ^ |
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      me too, I had to skip it and come back to it..

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Thanks problem B for negative Delta :)

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First task was pretty hard for div.2 ( Thanks for your time spent for making a contest)

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participating today was a bad idea

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I see a huge gap between C and D, but on the other hand there where still a lot of people solving D.

Maybe I missed some more or less obvious observation.

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    8 days ago, # ^ |
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    Yeah, you missed a small observation. Let's build array a based on array b from the beginning. So for every operation, we can add at most 2 elements into a. So for the current move, if the previous median is not equal to the new median then there cannot be an element in the array we build (a) whose value is in between the new median and the old median. Because if you add two unknown elements into array [1,2,3,4,5,6,7] then the median can be one of 3,4 and 5.

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8 days ago, # |
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Can someone please help me where I went wrong for bugaboo C? I was getting correct answer on test cases and I am pretty sure about the logic too. 118652416

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    8 days ago, # ^ |
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    Not sure how this is supposed to work dp[j] = max(dp[j], j / i);

    The ratio is arr[0][i]/arr[1][i], but not the mathmatical result of the division, but the fraction. So we need to divide both values by gcd(), and then count foreach position how much of them exist left of that position.

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      8 days ago, # ^ |
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      If the ratio of D:K upto position j is equal to that upto position i, then I am updating dp[j] to be the number of conntinous groups of size i which is j/i.

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        8 days ago, # ^ |
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        The issue is that the continuous groups can have different sizes.

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          Can you provide a testcase on which my code would fail?

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            8 days ago, # ^ |
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            Something like this DKDDKK

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              8 days ago, # ^ |
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              It gives 1 1 1 1 1 1. Isnt this correct?

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                8 days ago, # ^ |
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                Nope it should be 1 1 1 1 1 2

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                8 days ago, # ^ |
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                No, the last one is a 2, since we can split in first two letters, and last 4 letters. Both have ratio 1:1

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            8 days ago, # ^ |
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            Hmm, I used ur approach in the beginning and the following testcase did not work: 1 9 DDKDDDDKK

            The answer should be 1 2 1 1 1 1 1 2 2

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              8 days ago, # ^ |
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              How is it 2 at the last place? Shouldn't it be only 1 group? Or am I missing something?

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                8 days ago, # ^ |
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                DDKDDDDKK can be split into DDK and DDDDKK and both have 2:1 ratio.

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                  8 days ago, # ^ |
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                  Ohh, my bad. Got your point thanks!

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Many E's will fail today (at least 2 in my room itself) because they will print $$$-1$$$ instead of $$$10^{9}+6$$$ but I was too lazy to hack lol.

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    8 days ago, # ^ |
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    I don't think so, none of the powers of 2 modulo 1e9 + 7 has value equal to 0.

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Can't believe 3k people solved C

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    8 days ago, # ^ |
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    It was easy. Just needed to notice then ratio of D/K remains same as the total. After that its just binary search.

    C
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      8 days ago, # ^ |
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      YES!!! My code is based on binary search ,but i dont know why i cant pass

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      8 days ago, # ^ |
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      A safer approach than doubles is to store a pair <x, y> representing x / y. However be careful to store it in its reduced form, that is, where gcd(x, y) = 1.

      Also instead of binary search, we can just store the number of times we have encountered this reduced fraction when iterating from left to right.

      Implementation: 118610628

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        8 days ago, # ^ |
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        Wow nice luckily it passed, I have to be careful next time thanks for the heads up.

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    8 days ago, # ^ |
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    Its a pretty common idea that has appeared a lot (especially at the start of this year on Codechef) — having a map storing some property which becomes the same (or similar) for all valid ranges then checking for each right end. So I don't think its that surprising that a lot of people solved it.

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      8 days ago, # ^ |
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      Its a pretty common idea that has appeared a lot
      Can you please give one of those links?

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        8 days ago, # ^ |
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        I'm not really good at remembering problem names, but two examples of problems using the right end of a subarray idea, that are somewhat similar to this problem are:

        Mex Subsequence

        Sed Passwords

        There were 2-3 others ones I think (including some at a comparable difficulty to this C that didn't need dp), but I only remember the names of these two problems since I was involved with testing them.

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    8 days ago, # ^ |
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    C was easier than B. I think we have to just maintain the simplified ratio of D and K we got till now.

    Like 1:2 is same as 2:4 and which is same as 4:8 so, just divide D and K by gcd for that. As ratio of one part of the string must of equal to the ratio of complete prefix.

    But i feel B more harder than C. Although there was not much difference.

    BTW problem similar to B was also on HackerEarth Link

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    8 days ago, # ^ |
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    I don't think that C was 3k easy. Something else is going on.

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Hello,bro,may i ask how to solve Problem C ? Actually, i don't know the reason why i get wrong answer , :(

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    8 days ago, # ^ |
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    We just have to iterate through the string, keep track of num_of_D, num_of_K, and store their ratio (after dividing by gcd(D, K) iff D!=0 AND K!=0) perhaps in a map<pair<int,int> int> — and print the value of the map for each pair — soln https://codeforces.com/contest/1536/submission/118649389

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    8 days ago, # ^ |
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    Hint
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8 days ago, # |
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Out of curiosity, is there a way to solve D by sort of simulating the valid ranges $$$a_i$$$ could lie in using coordinate compression on $$$b_i$$$ plus something like a fenwick tree?

Something like when you initially place a new element we constrain it to lie between (-INF, $$$b_{i} - 1$$$] or [$$$b_{i} + 1$$$, INF), assume they initially lie at the left end and use a fenwick tree to count how many we can move to the right.

I know the intended solution using upper and lower value stacks is easier and more elegant but I'm just curious if such an approach is feasible.

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    I thought of following approach but could not implement, could someone tell if how to implement if their solution was similar :

    Spoiler
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    8 days ago, # ^ |
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    Yes, that is more or less what I did. Compress coordinates. Use a binary indexed tree to keep track of values that are fixed. All values from the input need to be fixed, and if values are repeating, it is enough to fix each value once. Values that are not fixed are either minus or plus infinity, and we keep track of the counts. So, iterate over the input array. The first value goes to the Fenwick tree directly.After that, for each value, check how many values so far were strictly larger (including values from BIT and plus infinities), strictly smaller (including values from BIT and minus infinities) and equal to the new intended median. If the value of the median was not fixed before, fix it. The remaining values (1 or 2 depending on whether we had to fix a new value in this iteration) become minus or plus infinity, depending which category is less numerous. After the assignment, check if the supposed median is actually a median.

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8 days ago, # |
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How to solve C ? I tried to iterate on divisors of count of 'D' and then finding the value for possible count for 'K' and then check if the ratio existed somewhere. But I kept wrong answer on Pretest2. my submission. What is the correct procedure to solve this sum ?

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    8 days ago, # ^ |
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    Even I tried to do the same but got WA on Pretest 2. :(

    118652416

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    8 days ago, # ^ |
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    The key observation is, that if we remove a prefix of given ratio, the remaining part has same ratio.

    So foreach position, we need to find the number of positions left of it with same ratio.

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    8 days ago, # ^ |
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    Create a map<pair<int,int>,int> where the key is the ratio, seen as a pair of ints instead of a double. Iterate through the string and keep two counters, current numbers of D (currD) and current numbers of K (currK), for every position in the string call x=gcd(currD,currK) and add one to map[{currD/x,currK/x}] and thats the answer for that position. You are counting how many segments are with the same ratio than your current position.

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    8 days ago, # ^ |
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    **if A/B = C/D = E/F then A/B = C/D = E/F = ... = (A+B+E+...)/(C+D+F...) ** Thus a prefix can be divided into Components if The count ratio of D and K in all the partitions is same as that of Prefix . How to Store Fraction in Their Simplest Form : simple form of x/y is X/Y = (x/G)/(y/G) where G=__gcd(x,y) . We Can use map to store the position of Last index where the ratio was {X,Y} if the ratio at any index is i {a,b} the ans[i] = 1 + ans[pos[{a,b}]]; pos is a map.

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    8 days ago, # ^ |
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    Notice that the D/K ratio of any prefix remains the same as its optimal partition. Also for such a prefix it suffices to greedily find the smallest prefix that satisfy this value of D/K. This can be precomputed. Then use binary search to find the total elements with same ratio uptil index i and print the answers for every prefix online.

    Proof that D/K ratio is a constant :

    $$$\sum\limits_{k = 1}^MD_i + \frac{yD_i}{x} = L$$$

    Here M is the optimal partitions Di are number of D in prefix of length L and the fixed y/x is the ratio of K to D

    Code :

    C
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    8 days ago, # ^ |
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    Move along the array from left to right and for each prefix, find the ratio of D/K (rounded down to simplest form). Maintain a map to count the number of occurrences of this ratio and then the answer for index i is simply mp[ratio] + 1. It is always better to store the ratio as a pair of numerator and denominator to avoid division by 0.

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    8 days ago, # ^ |
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    Suppose when iterating from left to right, at index $$$i$$$, we have $$$cnt_D$$$ occurances of $$$D$$$ and $$$cnt_k$$$ occurances of $$$K$$$.

    Now let us note that for a given string, if all the components have the same ratio $$$x:y$$$, then the total string will also have the ratio $$$x:y$$$. So it is sufficient to check for only this ratio.

    Now the answer is just many prefixes till index $$$i$$$ has a ratio $$$x:y$$$ occurred. This works as if for some $$$j \lt i$$$ $$$x_{j}:y_{j}$$$ and $$$x_{i}:y_{i}$$$ have the same ratio, then $$$x_{i}-x_{j}:y_{i}-y_{j}$$$ must have the same ratio. So we can just count this using a map of pairs $$$(x, y)$$$

    However we must also take care of the fact that $$$x:y$$$ and $$$kx:ky$$$ are the same ratio. To do so we can just reduce the ratio to its lowest form by dividing both terms by $$$gcd(numerator, denominator)$$$.

    Code: 118610628

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8 days ago, # |
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There should be a bugaboo named "Omkar and hard contest"

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Thank you for the contest!

I kinda feel like C and D should be swapped, but then again it's kind of my fault I didn't start reading D after getting stuck on C I guess.

Anyway, it's not really much of a problem, the bugaboos were IMHO still good!

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8 days ago, # |
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Well, Problem E seemed really difficult at first. But the solution is merely two lines!

Solution
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8 days ago, # |
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How to solve E ?

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    8 days ago, # ^ |
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    I didn't submit since I was too late, but my solution got the samples correct.

    Spoiler

    UPD: Idea got AC post-contest

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    8 days ago, # ^ |
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    So, basically, you fix each hash to be 0 or non-zero. Now, which elements in matrix are zero and which are non-zero. Now, suppose you fix the hash at position (i,j) in the matrix to be non-zero, then the value of (i,j) will be the manhattan distance to the nearest zero. My proof is quite tedious but try proving it by contradiction.

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I just want to know , whether i will have any rating change , if i didn't submit a single line of code, no right no wrong??

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8 days ago, # |
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too many redudant statement, can't understand problem C :(

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trollest contest on cf

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spent a lot of time on A , then thought "they did not mention to give an optimal solution" so i just printed 0 to 100 for every case without negetive values and voila , answer accepted . is that an acceptable bugaboo? hmmmm .

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My submission to A is totally not legit (TLE), but I managed to pass system tests anyway. Here's my video of the round: https://www.youtube.com/watch?v=dXS6nNiYeZs

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8 days ago, # |
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meet a new cheater This is how kedos123 bypasses Plagiarism testing.

I am watching him from so many contest , He has done this today and in previous contest, and I am sure he must have done it multiple times before as well. People like kedos123 are spoiling the sport. I don't understand where would cheating take them in life. They will never get anywhere in life but always remain what they are i.e cheater. He should be banned from the platform as soon as possible . MikeMirzayanov sir pls ban him and skip his solutions .

todays submission 118639631 118614794 saw his submission time , he is that much pro that he can solved problems in 2 minutes .

kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++;kedos++; jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++;jai++; jai++;kedos++;jai++;jai--;kedos--;kedos++;kedos++;jai--;jai++;kedos++;jai++;jai--;kedos--;kedos++;kedos++;jai--;

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How the hell was B approved?! Such an annoying to code problem. The average problem-A on CF requires more thinking than that. I liked C, A today and have almost no clue why my D or E passed. Seemingly dumb guesses that I can't prove.

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Can anyone give some hints for D?

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    8 days ago, # ^ |
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    Whenever you add the two new integers, you have three options.

    1. Add them to the left of the previous median. This results in shifting the median one to left.
    2. Add them to the right of the previous median. This results in shifting the median one to the right.
    3. Add one on either side. Same as previous median.

    Try to think of the situation where the answer would be "NO".

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How can https://codeforces.com/contest/1536/submission/118604068 solution pass if the question doesn't say we can remove the element?

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    8 days ago, # ^ |
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    Which element is removed? All the required elements are present.

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    8 days ago, # ^ |
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    if the given array contains negative elements then the answer is NO, otherwise just print from 0 to 100, it will always contain the given array

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      8 days ago, # ^ |
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      oh sorry, I am totally BLIND.

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      Damn, I actually constructed the array by using set and vector. Didn't see this observation!!

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    if (neg) { std::cout << "NO\n"; }

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stories (short or big) in problems are good if they can somehow help in imagining. In A,B,C,D if problems were without stories then it would have been good.

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In C I somehow thought I should split the prefix evenly which waste a lot of time of mine :(

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Strong Pretests !! :|

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My opinion about C:

WTF is this explanation ?!! if someone couldn't understand the explanation then he'll see the samples, that's what I did but the sample explain another problem !! I (and I think a lot of peoble) understood it like every segment should have the same number of 'K's and 'D's.

question for the authors: couldn't put a good sample to explain another cases ??!!

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    The explanation could have been simpler i guess..

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    Exactly, I also understood the problem to be this, and could not come up with why it is not passing for about 1 hour.. before realizing that the ratio are compared in simplest form.

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Can somebody please tell me why 118638104 gives run time error on test case 2?

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    8 days ago, # ^ |
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    a<0 && lol!=true once this condition is met it will always goes into else case but when there is a second negative number isit[neg] will throw RTE

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Did anyone tried to solve C using sieve? My Attempt — 118650015

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118650415 why TLE? Problem -: B

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    8 days ago, # ^ |
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    Use m.find(g)==m.end() instead of $$$m[g]!=1$$$. This is the cause you are getting TLE. In map, [] operator store the key, then check value.

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EBACDF

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    8 days ago, # ^ |
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    Really! was E that easy??

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      at some moment during solving I just realized that placing zeroes goes to unique table, then submit, then "LOL why it is E?"

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    E isn't that easy if you don't intend on finding a pattern. But anyways, agreed.

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    True!!

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    for that, you need to be in the same room as your alt which is close to impossible. This is only possible in the educational round where there is a separate hacking phase.

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Random fact: B can be solved in $$$O(n*|\Sigma|)$$$ using dp on suffix automaton (code). This approach can solve the problem even if $$$n\leq 10^6$$$.

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My code for B. It is most likely to get MLE in SysTests. Can somebody say, why the memory usage has skyrocketed?

UPD: It passed :'). Still, can somebody tell why the memory usage has skyrocketed? I have used simple brute force.

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While I'm practicing problems with difficulty 2500, it's very sad that I couldn't solve even C. I didn't have a good observation to solve D either. Not sure what's wrong with me...

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    8 days ago, # ^ |
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    you are me+(300-500) cf rating. i am solving so many 2000 problem and still took so much time to solve B, but solved C just by looking at it

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Weak Pretest in Problem 1

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Problem A and C are hard to implement :)

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    turns out you can just print from 0 to 100 for A if there isn't a negative element in the array

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118650415 why TLE? Problem -: B

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    8 days ago, # ^ |
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    Although you know that it will run at most n time for any string (worst case: consecutive subsequences) but there's still some additional calculation in the loop so you need to break all the outer loop after you have found the answer.

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      I just added a break after checking a single character if the ans is present and it gave accepted ... its worst complexity is still O(26*26*26) . How it is possible?

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        8 days ago, # ^ |
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        unnecessary loops for each test case are huge when you don't break after you have found an optimal solution.

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          8 days ago, # ^ |
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          And if there is a huge test case with answer of 3 characters then? will it no give tle? Btw thanks for helping

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How to approach slightly modified problem C, if it is asked to find the number of ways to split such that the ratio (D/K) should be the same?

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    8 days ago, # ^ |
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    if I understand your question correctly, isn't it just $$$2^{ans - 1}$$$ for each prefix?

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very nice problems! E was unfortunately very proof-by-AC-able, but the actual induction proof is super clever

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Dang, I feel like an idiot. When solving A, I didn't realize that the version of Python 3 on the server only supports the 2-argument version of math.gcd(). It took me 17 minutes and 7 wrong submissions to debug this simple error.

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    8 days ago, # ^ |
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    One more thing to add here. CF states that it is using CPython version 3.9.1, but if you run

    import sys
    print(sys.version)
    

    you can see that the actual version is 3.8.1. The updated feature to math.gcd you wanted to use was added in Python 3.9. So I'd argue CF is definitely at fault here by mislabeling its version.

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When will the ratings be updated??

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Idea for E:

Fix which #s turn into 0s.

All other numbers are uniquely determined. Imagine a multisource BFS from every 0. The value of a certain cell is simply its distance to the closest 0.

Answer is 2^X, where X is the number of #s (Edge case if there are no 0s in the original matrix. Then the answer is 2^X-1).

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    8 days ago, # ^ |
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    Can you explain to me how is the answer 2^x ? Test case like ##0 when doing 2^x that means at some time the test case will become 110 and it doesn't follow the second constraint of the problem, so how is it 2^x ?

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      For your input the answer is 4, and 110 doesn't appear: 210, 010, 100, 000

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I had written correct logic for Problem C during the contest but it was exceeding time limit just because standard print method of Java was not fast enough for the given constraints. Isn't it unfair for non-C++ coders !! The constraint of 2 * 10^5 is carefully chosen to avoid these language specific problems and is widely used. I wonder why it was not considered during the testing phase!! :( golions

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    8 days ago, # ^ |
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    We have model solution in Java. In the future I recommend that you use StringJoiner or StringBuilder when outputting a lot of numbers.

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how can the last output for this test

test

be 2 ? you cannot even divide a string of length 9 in 2 equal chunks .

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    [KKKDDK] and [DKK] ratio is 1/2

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    8 days ago, # ^ |
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    You don't have to equally divide the chunks.

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      8 days ago, # ^ |
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      then why is it written this ? Both brothers act with dignity, so they want to split the wood as evenly as possible. as far as i understand english " Even distribution " means equal distribution of something . Thanks to the problem setters you guys have written some beautiful problem statemnts .

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        8 days ago, # ^ |
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        It is crearly explained afterwards that ratios should be equal, not exact numbers

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8 days ago, # |
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https://codeforces.com/contest/1536/submission/118611087 never thought that I would fail in brute force can there be new rating category named 'noob' for people like me :)

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8 days ago, # |
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Problem E is virtually equivalent to 2013 USAJMO Problem 2: https://artofproblemsolving.com/community/c5h532231p3041818

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8 days ago, # |
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To not keep you waiting, the ratings updated preliminarily. We will remove cheaters and update the ratings again soon!

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8 days ago, # |
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I will be green again once cheaters are removed :) . Just 1 point away from being green again .

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8 days ago, # |
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WILL USING PRIMES FOR C WORK OR WILL IT GIVE TLE?

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8 days ago, # |
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road to purple!!!

first milestone reached, feeling fucking A. Lets go !!!!

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    8 days ago, # ^ |
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    yo same! good luck man, I'll see you in purple :)

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8 days ago, # |
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Isn't "aaa" lexicographically smaller than "ac" according to rule 2 from Problem B. Can anyone explain why this is not correct?

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    8 days ago, # ^ |
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    It has more characters

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    8 days ago, # ^ |
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    But it's longer than ac, in the problem it needs the shortest one.

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    8 days ago, # ^ |
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    Because in statement it is said that: "The MEX of the string is defined as the SHORTEST string that doesn't appear as a contiguous substring in the input." So mex is string of length two, and if there are more than one string of length 2, that sutisfies the condition of mex, than you should pick the lexicographically smallest among those(of length 2).

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      8 days ago, # ^ |
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      I guess I was more focused on the lexicographically smallest part and missed the shortest Thank you.

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    8 days ago, # ^ |
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    btw if it was based on lexicographically smallest, the answer would always be a prefix of the infinite string: aaaaaa.... lol

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8 days ago, # |
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Problem E Explanation shows Math Processing Error in Major Browser like Edge, Chrome or Opera. How can I get rid of it?

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7 days ago, # |
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Can anyone tell what is the best method to generate strings like a,b,c.....z,aa,ab,ab.....az,ba,bb..... and so on in problem B and store in a vector? What is the easiest method? Please share your piece of code.

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    7 days ago, # ^ |
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    7 days ago, # ^ |
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    wasn't able to solve this problem during the contest but after the contest I search for this and luckily found this beautiful way to generate all substring and solve this problem

    string MEX(string s,int n){

    vector<string>substrings;// will store all substring in sorted order
    substrings.push_back("");
    while(true){
        vector<string>temp;// stores all substrings generated in this iteration 
        for(auto c: substrings){// iterating over all subtring 
            for(char i='a';i<='z';i++){
                string str = c;
                str.push_back(i);// adding a,b,c one by one to generate new subtring
                temp.push_back(str);// pushing in temp to use it on next iteration
                if(s.find(str) == string::npos){
                    return str;
                }
            }
    
        }
        substrings.swap(temp);    
    }
    return "";

    }

    Example to understand clearly

    initially, substring contains an empty string we are adding a,b,c...z, one by one to "" and pushing back to temp so temp contains {a,b,c,d.....z} now swap temp and substring Now substring contain {a,b,c,.....z} here the magic happens Now you will extract a (first element) and again add a,b,c...z, one by one so the new substring becomes aa,ab,ac...az you will do the same thing for b,c,d....z so Now temp contains all subtring possible with two char

    Hope you understood it

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    7 days ago, # ^ |
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    Check out the increment function in the my submission

    It just takes in any random strings and make it work like a counter.

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    7 days ago, # ^ |
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    I use recursion: 118607108

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7 days ago, # |
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Can anyone tell me the rating of each problem and the best time complexity to solve the problem New to CP, was able to solve only 1st problem also what kind of contest should I give as a beginner?

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7 days ago, # |
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ass

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7 days ago, # |
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Please check these two Submissions for Problem 'C' :-
1.) https://codeforces.com/contest/1536/submission/118643260
2.) https://codeforces.com/contest/1536/submission/118699081
Logic is same in both but in 1st submission, I used ratio (in double) as key and in 2nd, I used pair as key of unordered map.
1st one got accepted but 2nd one is giving TLE.
Please Check them ...

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    7 days ago, # ^ |
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    Your calculation of hash of pair is poor. Do not combine hashes using simple xor as x ^ y. Use constructions like: x ^ (y + 0x9e3779b9 + (x << 6) + (x >> 2)) or x + y * 1000000007 (in this case you can use some prime number instead of 1000000007).

    And it pass testes: 118753875 and 118754141.

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6 days ago, # |
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This contest's sytle is so strange than others.Almost every problem I had to find the law behind the title ,it's very easy if we find the law ,but if we cann't find the law ,it's very puzzling!...

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5 days ago, # |
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Codeforces is fun.

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5 days ago, # |
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Attention!

Your solution 118628482 for the problem 1536B significantly coincides with solutions Foundnt_Alice/118625677, Believeu_us/118628482. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://codeforces.com/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

I have not cheated at all and two or more person can have same approach for the above problem as it was just about bruteforcing.Neither I have used any public code or ideone.com.You can also check my other codes.Please dont skip the solutions As it is a clear coincidence.MikeMirzayanov Please look into it.

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5 days ago, # |
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Respected MikeMirzayanov I received a message from Codeforces that my solution for 1536B significantly coincides with with solutions of several other contestants. But speaking honestly, I use codeblocks for all my coding C++ contests and neither have I helped someone during the contest nor have I taken help from someone. I think this a case of mere coincidence because never have I ever been penalized for such deeds on Codeforces and I am an individual coder. Can you please look into the matter once again and tell me what should be done..

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4 days ago, # |
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Won't the cheaters be eliminated in this round ?

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4 days ago, # |
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Bangla Tutorial

Problem D: Omkar and Medians

Link: https://www.youtube.com/watch?v=VgdsXBeY8Qw

Specially anyone from Bangladesh can understand.

Thanx to all.