atoiz's blog

By atoiz, history, 4 weeks ago, In English

(Translation: Hello)

We are very happy to invite you to take part in our contest, Codeforces Round #666 (Div. 1) and Codeforces Round #666 (Div. 2). The contest starts on Aug/30/2020 17:35 (Moscow time) and lasts 2 hours. In both divisions, there will be 5 problems for you to solve.

The problems were authored and prepared by Maripium, DatVu, MofK, and me.

We are very grateful and would like to sincerely thank the following people for their assistance in preparing the round:

Finally, we would like to thank all of you for participating in the contest!

We have spent many months to brainstorm ideas, ended up discarding most of them, and finally chosen our best ideas to compose together this contest, so we hope you will enjoy our round! (and hope the Devil's Number won't haunt our round XD)

Good luck, have fun!

The score distribution will be announced later.

UPD1: Here is the score distribution:

Div. 1: 500 — 1000 — 1750 — 2250 — 2500

Div. 2: 500 — 1000 — 1250 — 1750 — 2500

Hope the long queue disappears soon :'(.

UPD2: Congratulations to the winners:

Div.1

  1. tourist
  2. Radewoosh
  3. aid
  4. ksun48
  5. Um_nik

Div.2

  1. chokottodake
  2. 1092515504
  3. mickey639
  4. matt64
  5. zjjcth330

We apologize for the late editorial. Anyway, here it is: Editorial

 
 
 
 
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  • Vote: I do not like it

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

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

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    4 weeks ago, # ^ |
      Vote: I like it +47 Vote: I do not like it

    how do you edit others post?

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      4 weeks ago, # ^ |
        Vote: I like it +69 Vote: I do not like it

      I'm coauthor

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

        I was not aware of this feature, but indeed you can now add co-authors of the blog post. Thanks

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

        The question levels jumped a lot from 1st to 2nd. 2 Div.

        Hoping gradual increase next time.

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

        Do co-authors receive upvote contribution?

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          4 weeks ago, # ^ |
            Vote: I like it +27 Vote: I do not like it

          Good question! But the answer is no. I also hope cf will have this feature.

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

            But there are many problems with that. For example, someone may write a blog post and put all his friends as co-authors and they all get free contribution.

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              4 weeks ago, # ^ |
              Rev. 3   Vote: I like it -15 Vote: I do not like it

              maybe we can set a limit to how much co-authors can get

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

              The total contribution should be divided among the author and co-authors in some ratio, that will solve the problem :3

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +13 Vote: I do not like it

    https://codeforces.com/contest/1397/submission/91390761 This is my submission of question div2 B, and it returned the wrong answer in the eighth test case. I changed the compiler to VS C++ 2017, and the result was ACCEPTED! Can this question be judged again?At least, can you tell me where is my mistake? thank you very much. UPD:I changed the compiler to GNU C++14 and GNU C++17, and the results are accepted.

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      4 weeks ago, # ^ |
      Rev. 2   Vote: I like it +19 Vote: I do not like it

      There is one abs() outside namespace std and that abs() doesn’t support long long as argument. Change your code to std::abs() and it should work fine. 91432176

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

        Finally I know where the problem is,It took 421 ms on test case 5, and I finally know why. thank you very much.

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

        hey i have the doubt ,during contest my submission 91394398 got passed through pretest and i got the points of the 2nd question but after the contest ended it says your code fails at test case 27 and the points of 2nd question were removed . So the problem is that if during contest it didn't shows that code is wrong and pretests are passed then how would i able to correct it.

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

          There are pretests(which are tested during contest) and system test (real test, which are tested after contest is over). Pretest passed does not guarantee solution being accepted(= accepted in system test), since latter has larger test set.

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

      my code I get a strange bug in my code: In for loop,I wrote "if(temp<=0)break" to avoid overflow, but it doesn't work. Hope someone can give me explanation,thanks in advance.

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

        Signed integer overflow is undefined behaviour in the c++ specification. This lets the compiler prove that for all defined behaviour that if statement is true (as both temp and p are always >= 1) and optimises the check away (as either the values are small enough to be defined behaviour or it's undefined and the compiler can do whatever it wants).

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

As a Maripium fan, I want to start an orz chain.

Maripium orz.

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4 weeks ago, # |
  Vote: I like it +88 Vote: I do not like it

Will this contest be Lucifer themed?

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4 weeks ago, # |
  Vote: I like it +107 Vote: I do not like it

I tested this round when I was blue!!! xD

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    4 weeks ago, # ^ |
      Vote: I like it +200 Vote: I do not like it

    After this round I will be blue!!! xD

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      4 weeks ago, # ^ |
        Vote: I like it +58 Vote: I do not like it

      666 is the devils number, you will become orange :XD

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

      How good it'll be if you and me will have the same colour after this round.

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

        Almost impossible! As max rating change for him as per his current performances will be in rang almost -200 to +200 . Same applies to you as well Thus you were close to make that change , for you to reach blue and for him to reach blue there is a sufficient gap of 40 to 50 points. Anyways good luck to you for a big delta change !

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      4 weeks ago, # ^ |
        Vote: I like it -16 Vote: I do not like it

      Really?

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

      devil was right

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +24 Vote: I do not like it

    I tested this round when I was blue (well I still am).

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

    I am curious that how different country people conduct around together! As you are an Indian, the coordinator is from Canada, and the other guy belongs to a different country too!

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

      Well, there are specific Discord servers set up for co-ordination.

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

      its because we people have a wonderful sleep schedule :)

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

    Nice

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

You know the guy gives no F's when his handle name is something like user202729_

Damn bro , You have the most interesting uninteresting handle name I've ever seen

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4 weeks ago, # |
Rev. 2   Vote: I like it +136 Vote: I do not like it

As an author of Round 666, I just want to say that right now I have exactly 666 friends on Codeforces!

Edit: Wow, it lasted a whole 3 minutes! Now I have 667...

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

    Plot Twist: This was a plan to get more friends using reverse psychology

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

OMG!!!! 666 round, so scared!! OMG

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4 weeks ago, # |
Rev. 2   Vote: I like it +28 Vote: I do not like it

♫ 666 the Number of the Beast
Sacrifice is going on tonight ♫

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

WOW! palindrome round.

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

What’s devil’s number?

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

    666 is the devil's number or also referred to as 'number of the beast'

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

300iq seems like having an Asia tour on Internet and now he is arriving at Vietnam.

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4 weeks ago, # |
Rev. 2   Vote: I like it +25 Vote: I do not like it

Others: " I know coding "
LGMs: " Coding knows me "

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

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4 weeks ago, # |
  Vote: I like it +76 Vote: I do not like it
  1. $$$666 = \sum\limits_{i=1} ^ {36} i$$$
  2. $$$666\times 69$$$ is a palindrome.
  3. Look at my profile picture. I also recorded a video of it happening.
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    4 weeks ago, # ^ |
      Vote: I like it +61 Vote: I do not like it

    Also, 666 is the sum of squares of first seven primes

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +92 Vote: I do not like it

    One more, 666 is the sum of the first 144 decimals of π.

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    4 weeks ago, # ^ |
    Rev. 4   Vote: I like it +26 Vote: I do not like it

    Also 666 is the smallest positive number to have 3 sixes.

    Also, rotating 666 by 180 degrees clockwise/counterclockwise gives us 999 which is the smallest positive number to have 3 nines.

    And also , (180 degrees rotated 666)-(666) gives us 333 , which is the smallest positive number to have 3 threes.

    And also, ((180 degrees rotated 666)-(666))*666/(180 degrees rotated 666) gives us 222 which is the smallest positive number to have 3 twos.

    Okay,Now I'm tired. Basically we can generate all smallest numbers having 3 same digits using 666 and it's rotation. :P

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    4 weeks ago, # ^ |
      Vote: I like it -37 Vote: I do not like it

    left-handed? cringe

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

    You use the mouse with your left hand, on the right side of the keyboard???

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

    Hexakosioihexekontahexaphobia is the fear of the number "666."

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

      Hippopotomonstrosesquippedaliophobia is the fear of long words

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

5 problems and div.1 & div.2 looks like round is going to be tough.

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4 weeks ago, # |
  Vote: I like it -35 Vote: I do not like it

hope pretests passed => main tests passed

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +43 Vote: I do not like it

    It is almost impossible to do that unless you have pretests=tests and 0 hacks or the problem was solved by a very small number of people. For example, look at Codeforces Global Round 9. Here are the FST rates:

    A: 24/7357

    B: 10/6890

    C: 81/5225

    D: 35/2046

    E: 0/352(pretests=tests)

    F: 3/263

    G: 1/97

    H: 0/7(7 is a very small sample size)

    I: 0/0(duh)

    Overall, it makes sense to wish for strong pretests(but don't do it in a cf comment unless you want downvotes), but pretests passed -> main tests passed has almost no chance of happening.

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

      Does all hack-Cases are included in main tests or it depends on setter committee to decide which tests to include for system tests?

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

        One of the contest managers needs to press a button to add a hack into the system tests, but I don't think there's any case where that button wasn't pressed.

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4 weeks ago, # |
  Vote: I like it -30 Vote: I do not like it

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

rip Devil

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

six six six

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

six six six, nice round, :) from VietNam with love <3

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

Maripium org

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

How many languages does 300iq plan to master?

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

atoiz orz

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

Wow Rated contest after a long gap,Contest is seems to be very Interesting...

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4 weeks ago, # |
  Vote: I like it -15 Vote: I do not like it

Hope for strong pretests.

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4 weeks ago, # |
  Vote: I like it +42 Vote: I do not like it

This is the last contest I can play before school starts. (T_T)

Then I will become Candidate Master!

QQ图片20200829125713.gif

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

    yo man! i'm still newbie here T.T how can i be like you? :<

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      4 weeks ago, # ^ |
        Vote: I like it +94 Vote: I do not like it

      YO man! i'm STill mAStER heRe T.t hOw caN i BE Like you? :<

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    4 weeks ago, # ^ |
      Vote: I like it -15 Vote: I do not like it

    You will see, once you go to school you will learn many new things!

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

me when i see the image: chrome translate can translate image ???? :D ???? what is going on ????

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

Is div. 3 being discontinued or something? No div3 being held nowadays.

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4 weeks ago, # |
  Vote: I like it -18 Vote: I do not like it

Ya, From VietNam with Love. Good luck to the contest and for all

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4 weeks ago, # |
Rev. 12   Vote: I like it -42 Vote: I do not like it

excited for vietnamese contest

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

    vietnamese nha bro :))

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

      ok fine :)

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

      u'll get many downvotes because of speaking vietnamese here bro :v

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

        I didn't think that it's that big of a problem, based on this situation that they can easily find out that I was pointing out his spelling mistake :(

        I won't make that mistake again :))

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4 weeks ago, # |
  Vote: I like it -15 Vote: I do not like it

húuuuuuuuu!!!!!!!!

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

this week's only contest ...

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

This'll be a devil of a round

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

If this round isn't DOOM themed I will lose all hope in humanity.

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4 weeks ago, # |
  Vote: I like it +27 Vote: I do not like it

What is codeforces Round X? is it a new type of round?

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

    I think it implies that the date is decided for the contest but they still don't know if there will be additional rounds before that round, hence they have just named it Round X for the moment. If you see there is 18 days gap between Round 669 and Round X and most probably more rounds will be added in those 18 days gap, hence the name X.

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

      It is 2.5 hr long, so it is most probably a different type of round.

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

I hope to get the 666th place :)

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4 weeks ago, # |
  Vote: I like it +85 Vote: I do not like it

Here it is! +666

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

Why score distributions are announced later? I don't know the reason. Can anyone tell me?

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

Again,the long queue issue ..Waiting my solution to be executed...[user:MkeMirzayanov] Please look into it

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

Cant wait

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

WOW, Viet Nam :v

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4 weeks ago, # |
  Vote: I like it +20 Vote: I do not like it

Is the codeforces queue long just to make it feel like a bad omen?

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

Hope your first contest will not be ruined by the long queue issue. I have submitted a solution one hour ago and still, it's in the queue. Hope it will be solved before the contest.

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

Looks like problems from hell.

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

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

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

The queue disappeared!

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4 weeks ago, # |
  Vote: I like it -36 Vote: I do not like it

Me trying to get some rating in this round: Meanwhile the devil:

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4 weeks ago, # |
  Vote: I like it -35 Vote: I do not like it

Score distribution looks very scary.
B and C have difference of 250 points only
This indicates two types of round
1. Speed-forces
2. The hard one or unbalanced
Fingers crossed....

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

round-666 will be my 66 contest :D

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

Queue disappeared :) All the best everyone for the round.

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

To do well in this contest you have to listen to Iron Maiden not TWICE :P

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4 weeks ago, # |
  Vote: I like it -20 Vote: I do not like it

666 is a natural number :)

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

Hakuna Matata!!

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4 weeks ago, # |
  Vote: I like it -31 Vote: I do not like it

I had already got a correct answer in B at 34 minutes , I resubmitted now and it also passed but my timing has been updated according to present timing. PLease look into this

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

    you'd be judged based on your last submission time for any problem. it's part of the rules

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

      Why this rule? It just screwed my contest.

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

        Why did you resubmit?

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        4 weeks ago, # ^ |
          Vote: I like it +21 Vote: I do not like it

        It makes sense in ICPC style contests where you get your submission's final verdict instantly to make your submissions past the AC submission irrelevant.

        Here, the final verdict is supposed to be kind of hidden until the end of the contest (you might get pretests passed on a wrong solution). Only last submission counts rule is to stop the abuse of submitting multiple solutions hoping one of them would pass.

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

    Read the "Judging Solutions" part in the rules, point number 5 after the table.

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

    Meanwhile I cant even solve B

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

Is there a way to find the number of pretests in a problem?

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4 weeks ago, # |
  Vote: I like it +21 Vote: I do not like it

Reading E is so fun. haha

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

This really is a cursed round

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

After this round, I hate 666.

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

finally some interesting problems i love it!!

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

We have spent many months to brainstorm ideas, so we hope you will enjoy our round!

Duh

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

    ques2: 2 test case:: if c is 31625 then answer is 1999827749 (10^9-1+10^9-31625^1+10^9-31625^2)

    (it is less than given one and it also fulfill all condition)

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

      Are you sure 10^9-31625^2 is positive?

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

        But we can either increase or decrease the number so 10^9 can be raised to 31625^2 by adding 140625

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

          But the cost is 31625^2 — 10^9

          Not 10^9 — 31625^2

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

            I got it. I was doing silly mistake Thankyou for helping me.

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

Pretests for B :(

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

    Me too

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

    Wrong answer on pretest 4 :( As the contest is finished, I tried finding a number such that (num^(n-1))>=(biggest element of the array) using binary search and then using this num as C to calculate the answer. Can anyone help.

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

      I did the same! I also tried for mean and weighted mean. What my friend did was nice. From the constraints it can be seen that ans lies from 1 to 1e6, he just did binary search in the entire range.

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

      witcher98 I had the same mistake with binary search at first, I changed the search such that if(min==max){return min} and if(min+1==max){return max}, and it worked.

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

      Did the same bro, WA on pretest 4, my output comes smaller :D

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

Div1 C was really painful

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    4 weeks ago, # ^ |
      Vote: I like it -19 Vote: I do not like it

    Agreed, statement was very long.

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

    The statement looked so painful that after solving all the other tasks in div2 I decided to quit without approaching it

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    4 weeks ago, # ^ |
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    Disagree. The first impression was indeed painful, but the seemingly annoying parts disappeared quickly. Code is short and contains no strange special cases.

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      4 weeks ago, # ^ |
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      Hmm, my code doesn't look that short. Maybe I'we just done things in a too complex way

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      4 weeks ago, # ^ |
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      contains no strange special cases

      I'm very curious as to how you solved this problem, because my solution is case whack after case whack.

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        4 weeks ago, # ^ |
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        Are the cases only on paper or in the code too? Now I'm kind of worried that I'll fail system tests.

        My code
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          4 weeks ago, # ^ |
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          The cases are in my code, but I'm not sure if they're actually necessary or I'm just being a clown as usual.

          My code (apologies, I don't appear to know what line breaks are)
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    4 weeks ago, # ^ |
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    I dare to disagree with you. I think Div1 C was a beautiful dp problem.

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what is the pretest 4 of B.. Any guess ???

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How to solve B?? Should we brute force all possible values of c and then find minimum cost??

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    4 weeks ago, # ^ |
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    Yes

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      4 weeks ago, # ^ |
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      Yeah but how do you set the limit on maximum value of c.My logic gave WA on pretest 4.

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    4 weeks ago, # ^ |
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    Because c^i increases very fast, and the largest value of c is about sqrt(1e9). I brute force all value and exit when the cost is stop decreasing. View submission 91363571

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4 weeks ago, # |
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How to solve D?

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    4 weeks ago, # ^ |
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    Greedily. Actually I think it was easier than C

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

    Passed pretest by always choosing the pile with the biggest value. Let's see if it passes the system test.
    UPD: It passed.

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    4 weeks ago, # ^ |
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    If max_value > sum — max_value answer is T, else answer depends on sum % 2.

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

      I also came up with the same observation but forgot to write simple 'else' keyword in one of the conditionals while implementing, this gave WA and I thought this approach is wrong coz I didn't have a proof :(
      Adding up on this, I thought div2D cannot have such an easy solution so I was convinced this is the wrong approach :'(.
      Do you know how to prove it?

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

        its more like, if the sum is odd then its T, else u look at your first condition, because the first player can always take an element from the max pile, if the sum is odd then he definately wins bcs they will either take all the stones or when a single pile is left, he will be the one to take the stone from it, making the second player unable to take from it, and if the sum is even, then if the first player doesnt always take the max element, then the second player is left with odd sum and an option to take maximums, so then the second player wins, so the first one has to take the maximums in every step, so if the maximum pile isnt bigger than the sum of the rest of the piles then the second player wins bcs, else the first player wins, this is roughly it

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          4 weeks ago, # ^ |
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          Thanks, this makes sense. Btw how to prove it mathematically?

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            4 weeks ago, # ^ |
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            well, u can prove this more thoroughly by proving the fact that the first player can always take the max, but i dont know how to bring math in here

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4 weeks ago, # |
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Approach for B?

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    4 weeks ago, # ^ |
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    Sort the array in ascending order and find the two value of X(ceil and floor) for which pow(X,(n-1)) is closer to maximum value of the array. Let say you have an array [1,2,7] so the number whose (n-1)th power is closest to 7 are 2 and 3 (pow(2,2)=4 and pow(3,2)=9) now take these two values and iterate in the array and calculate what is the answer if we take 2 and if we take 3 and then print a minimum of these two.

    My submission 91391756

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4 weeks ago, # |
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whys is this Giving WA?

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4 weeks ago, # |
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Nice problem, like this round

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Please don't tell me that the constraints in D were so low only to confuse the heck out of me.

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    4 weeks ago, # ^ |
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    there was a solution in O(sum(a)^3)

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      4 weeks ago, # ^ |
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      Seeing the constraints made me think that the solution is dp. But greedy passed the pretests, can you explain the solution in O(sum(a)^3) ?

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        4 weeks ago, # ^ |
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        sorry, actually it`s O(sum(a)*max(a))

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I feel like dumb after i fixed the bug for C that i was missing n = 1, just a minute before the contest. Really painful.

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What is the logic in Div2 B

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    4 weeks ago, # ^ |
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    for n >= 62(max size of long long) the answer should be sum abs(a[i] — 1) else you just consider the powers of c till a[max](1 / (n — 1)) and calculate the answer

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      4 weeks ago, # ^ |
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      I got it, but can you please help me in finding x^(1/n). I know how to find x^n but never used x^(1/n) (without using inbuilt pow function)

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        4 weeks ago, # ^ |
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        I guess you can use Newton raphson's method or similar iterative approximation techniques

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    4 weeks ago, # ^ |
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    Use ternary search for appropriate c

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    4 weeks ago, # ^ |
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    Sort the array in ascending order and find the two value of X(ceil and floor) for which pow(X,(n-1)) is closer to the maximum value of the array. Let say you have an array [1,2,7] so the number whose (n-1)th power is closest to 7 are 2 and 3 (pow(2,2)=4 and pow(3,2)=9) now take these two values and iterate in the array and calculate what is the answer if we take 2 and if we take 3 and then print a minimum of these two.

    My submission 91391756

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4 weeks ago, # |
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Div2 C was by far one of the most interesting observations used on an ad-hoc problem.

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    4 weeks ago, # ^ |
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    Div2 C was a pretty darn clever problem, ngl

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      4 weeks ago, # ^ |
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      There was a similar one in a global round! Couldn't do it then!

      Upsolving helped :D

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        4 weeks ago, # ^ |
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        Can you give the link of the problem in global round?

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    4 weeks ago, # ^ |
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    I mean... You can't say "by far" and then say "one of the..." xD

    It was a super cool problem!

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      4 weeks ago, # ^ |
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      "By far" was for me... "one of the" for the more experienced people. Didn't want to declare something without allowing public opinion. :p

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    4 weeks ago, # ^ |
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    "It can be proved that the solution is always possible". Imagine if that hint wasn't there!

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Let's hope the main tests pass :P

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Could not solve even B this time :( Any idea on how to do it

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    4 weeks ago, # ^ |
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    Could not solve even B this time

    You're Not Alone.

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      4 weeks ago, # ^ |
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      a real relief to find that an expert(not for long time xD) is with me.

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    4 weeks ago, # ^ |
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    Sort the numbers ascending. Now if the list is like really long, like over 50 elements, the only c you have to consider is c=1, even for c=2 the last c**i will be way to big.

    For arrays under 50 elements, one can brute force all possible c numbers up to 10**5 and pick the best one. The search for c can be optimised using stricter upper bound and binary search but with generous time limit its not needed.

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      4 weeks ago, # ^ |
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      I implemented the same n=50 approach. Dont know what went wrong ;/

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      4 weeks ago, # ^ |
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      thanks ! i will try this method.i was trying to reduce the value of c by using value of n.Don't know why it gave WA on pretest 4 though

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      4 weeks ago, # ^ |
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      How can you use binary search?

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        4 weeks ago, # ^ |
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        Lets say the biggest c I have to consider is 10**6.

        I will start with c = 500_000, calculate the absolute difference and then I will check c=499_999 and c=500_001, if c=499_999 is better and c=500_001 is worse then it means I am overshooting, and have to reduce the c.

        Next I take c=250_000, check if I am overshooting or undershooting by checking c=249_999 and c=250_001, if I undershooting next c will be 375_000 etc.

        So like a slightly modified binary search with gradient checking.

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

          Are you assuming that as $$$c$$$ grows the result is continuously improving until it reaches the optimal value, and after that it is getting increasingly worse?

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          4 weeks ago, # ^ |
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          Can you prove that the function is increasing (for you to return true or false even with gradient checking)?
          I'm not sure if i'm convinced.

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    4 weeks ago, # ^ |
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    Me too, 3rd problem was clever though!

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4 weeks ago, # |
  Vote: I like it +269 Vote: I do not like it

I'm sorry guys, but Div1 C killed this round for me. The idea is straightforward, but dealing with all the details was too hard for me. Besides, I noticed that $$$r_1 \le r_2 \le r_3$$$ only 15 minutes before the end of the contest :(

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    4 weeks ago, # ^ |
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    Wow, didn't even notice it till the end, wrote min statements everywhere to handle cases for that ._.

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    4 weeks ago, # ^ |
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    $$$r_1 \leq r_2 \leq r_3$$$ — what?

    Although the solution without this constraint is too complicated as well.

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    4 weeks ago, # ^ |
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    I just noticed after reading your comment. Thanks.

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    4 weeks ago, # ^ |
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    The key observation for me (which I was missing for an hour) was that there exists an optimal solution that's ever only $$$O(1)$$$ steps to the left from the rightmost position reached. Once I got that, the solution became quite manageable.

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4 weeks ago, # |
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a video solution for problem c(seems good problem).

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Div2 B. Im trying to brute force. 1 < i < sqrt(max(list)) But I got TLE on pretest 4

How to approach it?

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    4 weeks ago, # ^ |
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    I used ternary search on $$$c$$$. Passed the pretests.

    EDIT: No it doesn't work that way. My solution failed in the real tests. There could be local minimas too, and I didn't think of that.

    The correct way to solve it is to notice that you can not have a value for $$$c^i$$$ for any number greater than 2e9. (As you can always select $$$c=1$$$). So, if you have $$$n$$$ numbers then you can find the upper limit of the range of values for $$$c$$$. That is,

    $$$up^{(n-1)}<=2e9$$$

    . To be more careful, I selected 1e10 instead of 2e9. So I got up = pow(10,10.0/(n-1)). Now you can go from 1 to up, and keep track of the minimum abs diff.

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

    Sort the array in ascending order and find the two value of X(ceil and floor) for which pow(X,(n-1)) is closer to the maximum value of the array. Let say you have an array [1,2,7] so the number whose (n-1)th power is closest to 7 are 2 and 3 (pow(2,2)=4 and pow(3,2)=9) now take these two values and iterate in the array and calculate what is the answer if we take 2 and if we take 3 and then print a minimum of these two.

    My submission 91391756

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4 weeks ago, # |
  Vote: I like it +171 Vote: I do not like it

What was the point of Div1C? It had a really long and complex statement, but once you understood what was actually being asked, it was easy and fairly uninteresting :/

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    4 weeks ago, # ^ |
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    Honestly, I don't see the point of Div2 BCDE either. The difficulty gradient was quite unbalanced.

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I implemented Div2 C at last moment is this code correct or still it require something else!

https://ideone.com/HJ3kDp

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    4 weeks ago, # ^ |
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    My idea is first we can make any possible number with two numbers whose gcd is 1. thus for each Ai I was trying to make -Ai. IN 2 operations by using n and n-1 length of segment in first 2 operations. In one remaining operation first remaining value was tackled by me separately thus a total of 3 operations!

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4 weeks ago, # |
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Out of curiosity, did anyone manage to get pretests passed on Div 1 C using the +1 / +2 dp and running an exponential brute force at the end instead of handling cases?

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4 weeks ago, # |
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Div2 C was nice :) took too much time to solve it

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Looks like solving linear congruences a∗x≡b (mod n) was an overkill for C lol.

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    4 weeks ago, # ^ |
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    Can someone explain how to solve it?

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      4 weeks ago, # ^ |
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      Yep. Actually all you gotta realize is that multiples of consecutive numbers can form any number.

      So step 1: Select 1 to n, and add -1LL*(a[i])*(n)

      Step : Select 1 to n-1 and add 1LL*(a[i])*(n-1)

      Now numbers 1 to n-1 must 0 by now. You can make the nth number 0 by adding (n-1)*a[n-1].

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        4 weeks ago, # ^ |
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        What a clever solution!!!

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

      For C: If we can make all a_i multiple of n then we can make all of them 0 in one step using -a_i.

      Now, a_i+(n-1)*a_i=n*a_i So if we select segment with length n-1 then adding (n-1)*a_i will make all element divisible by n.

      Using this we can make all element divisible by n in two step and finally 0 in last step.

      You should handle overflow issue and n=1 case carefully.

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        4 weeks ago, # ^ |
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        I can't believe I missed this observation :(

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Devil fooled me with div2A

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4 weeks ago, # |
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Someone, please explain B and C. In B I iterate over constant c until power(c,n) <= 1e18, and permutation I choose the sorted one.

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

    For C: If we can make all a_i multiple of n then we can make all of them 0 in one step using -a_i.

    Now, a_i+(n-1)*a_i=n*a_i So if we select segment with length n-1 then adding (n-1)*a_i will make all element divisible by n.

    Using this we can make all element divisible by n in two step and finally 0 in last step.

    You should handle overflow issue and n=1 case carefully.

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      4 weeks ago, # ^ |
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      Thanks, Got it! Can you tell me what's wrong in my B approach...

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        4 weeks ago, # ^ |
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        I will see it once i solve B successfully.

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    4 weeks ago, # ^ |
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    For B I tried all values of c until c^k < 10000000000, because A[i]<10^9 and and abs(A[i]- 10000000000) would be too big. my submission

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    4 weeks ago, # ^ |
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    For B : Sort the array in ascending order and find the two value of X(ceil and floor) for which pow(X,(n-1)) is closer to the maximum value of the array. Let say you have an array [1,2,7] so the number whose (n-1)th power is closest to 7 are 2 and 3 (pow(2,2)=4 and pow(3,2)=9) now take these two values and iterate in the array and calculate what is the answer if we take 2 and if we take 3 and then print a minimum of these two.

    My submission 91391756

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      4 weeks ago, # ^ |
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      What was the answer for Test case 2 ? The 10^9 one , I Mean the number they were power of ?

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        4 weeks ago, # ^ |
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        31622 and 31623 are the closest to 10^9 and 31623 will give us a minimum for 31622 2000017493, for 31623 1999982505

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Problems B and C gave me PTSD.

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It took me over an hour to realize that I was overflowing long long on problem 2. RIP.

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Could someone please tell what is the problem for my soln to B?

https://codeforces.com/contest/1397/submission/91418834

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How to solve Div2 D ??

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    4 weeks ago, # ^ |
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    I also wonder how to do it. Could someone tell me what the meaning of this sentence : "if the current turn is the first turn then the player can choose any non-empty pile" . Could HL pick the first pile if T pick the first pile at first?

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    4 weeks ago, # ^ |
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    On every turn the player should pick the biggest pile, if he can't, try the next pile, if he still can't the other player wins. you can just simulate the process.

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    4 weeks ago, # ^ |
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    it's a parity problem but with a twist

    scenario 1: Both players can pick from any stack regardless — Then T wins if the total number of stones is odd and HL wins if total number of stones is even

    scenario 2: Each player can not pick from the stack the other player just picked — same as scenario 1 but on the condition if (size of biggest stack) > (size of rest of stacks added together) then T wins automatically since he picks first.

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4 weeks ago, # |
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Some people complained that the pony round had long problem statements

Ha-ha.

Look at Monster Invader. That is how you write long statements

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4 weeks ago, # |
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For correct solution, the timing is updated ,for incorrect it is not updated. Why the rule that the recent solved timing would be considered ?I solved Problem B nearly 30 min from the contest and then at last just to conform ,it resubmitted it with a small change so that it does not fail system test and it updated my timing. Why not make it something like If the first correct attempt fails, then the next one is considered. Also for who are new to codeforces at least the link of the rules could be included in the contest posts.

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    4 weeks ago, # ^ |
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    plz tell approach for B...?

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    4 weeks ago, # ^ |
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    Link to the rules is there when you register.

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      4 weeks ago, # ^ |
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      I actually register just 5 minutes before the contest seeing whether I could give that round or not

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    4 weeks ago, # ^ |
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    You make changes so that it does not fail system test. So your first solution is potentially not correct. So I surely agree to the rules.

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      4 weeks ago, # ^ |
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      And if someone makes wrong submission then is he not doing changes.

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    4 weeks ago, # ^ |
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    Why not make it something like If the first correct attempt fails, then the next one is considered

    Then everyone will submit multiple solutions to 'secure' AC.

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      4 weeks ago, # ^ |
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      You can then also charge him for his previous wrong submissions.

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    4 weeks ago, # ^ |
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    If you do not want you do not have to submit twice.

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

    "Why not make it something like If the first correct attempt fails, then the next one is considered"

    Yeah. And if this one fails too, let's move on to the next one. Let's give participants infinite number of attempts to bypass system testing in case they're uncertain.

    "And if someone makes wrong submission then is he not doing changes."

    If someone makes wrong submission then this solution is definitely not a candidate for system testing. And I believe in most of the cases it is a mistaken submission of a completely different task

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      4 weeks ago, # ^ |
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      If the test cases are strong then obviously only correct solution will pass which don't pass can be skipped in system tests.

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

        Thinking that strong pretests cover all possible cases and give you absolute guarantee is a plain bullshit and naivety

        One hacked solution does not mean pretests are necessary bad. It just means that the solution is hacked. No more, no less. Similarly with system tests.

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

I've written a fairly straight-forward brute for B.

Could someone tell, if i'm missing something? Solution Failing on TC3

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it -7 Vote: I do not like it

    [deleted]

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

      I have put a break condition in case the c^i overflows. also, since the biggest c is 10^5, a negative check for overflow should have done the job.

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

      Found the mistake! The negative check is wrong! It'd overflow multiple times

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4 weeks ago, # |
  Vote: I like it +42 Vote: I do not like it

Was I the only one to not attempt Div-1 C seriously initially considering its low number of submissions in the beginning?

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4 weeks ago, # |
  Vote: I like it +26 Vote: I do not like it

Who else skips a heart beat when you go to the Dashboard during system tests and you see RED on your problems? (and 1 second later realize/remember it's just the bad attempts).

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

Although I couldn't solve C, looking at its solution, I can say it's a pretty coo