lewin's blog

By lewin, history, 4 weeks ago, In English,

Hello everyone!

Another year has gone by. The last Codeforces contest of this year will be tomorrow, 29 Dec, 15:35 UTC.

The round details:

  • combined div1+div2
  • 8 problems
  • 2.5 hours
  • rated!!!

I'd like to thank the following people for helping with the round: KAN, winger, AlexFetisov, zemen, xiaowuc1, MikeMirzayanov. Without them, this round would not have been possible.

Scoring distribution will be posted later. Make sure to read ahead on the problems, since there may be some later problems that are easier for you. I hope to see you all at the contest, and good luck on the last chance to increase your rating this year!

EDIT1: The scoring distribution is 500-750-1000-1750-1750-2000-2750-3500

EDIT2: There will be a five minute delay for starting.

EDIT3: Editorial is here: http://codeforces.com/blog/entry/56713

EDIT4: Congratulations to the winners!

  1. Petr
  2. dotorya
  3. V--o_o--V
  4. Radewoosh
  5. Endagorion
  6. rng_58
  7. PavelKunyavskiy
  8. moejy0viiiiiv
  9. mmaxio
  10. Reyna
 
 
 
 
  • Vote: I like it  
  • +1310
  • Vote: I do not like it  

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4 weeks ago, # |
  Vote: I like it -54 Vote: I do not like it

Is it rated or not?

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

    yes is rated!!!! , this is clarificated in the round details.

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

Be careful, you wrote "17:35 UTC" instead of "15:35 UTC".

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

Expert this contest!! Good luck to all and have fun, hopefully 7k will participate. Thanks Mike for everything this year.

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

Mathematically speaking, would the ratings of Div2 participants be affected in any way in a Div1 + Div2 contest as opposed to only Div2 contests?

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4 weeks ago, # |
  Vote: I like it -41 Vote: I do not like it

"Make sure to read ahead on the problems, since there may be some later problems that are easier for you." — smelling something fishy. Hoping it will a be memorable contest.

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

What does the Good Bye contest say: "Long time no C"

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

"Make sure to read ahead on the problems, since there may be some later problems that are easier for you"

Love the suspense! Can't wait!

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4 weeks ago, # |
Rev. 2   Vote: I like it +14 Vote: I do not like it

Can't wait to participate the contest, if I don't drop to div2 I can then finally propose a CodeForces contest. :D

Note to self: Don't stay overnight for a programming contest ever again.... ZzzzzZZZZzzzz

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    4 weeks ago, # ^ |
      Vote: I like it -28 Vote: I do not like it

    Well, will that contest be rated?

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

    You can propose a contest if you are expert.

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

      Except it would take me another 15 contests to propose one. :/

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

        Serious question, do they give priority to Div1 problemsetters over Div2? If so I didn't know.

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

          I don't know, but they probably give higher priority to high quality questions?

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

          According to the coordinator, proposals are reviewed in "the order in which they appear on the list," which is most probably chronological order, I suppose.

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

This was a fun contest,let’s have more combined contests!

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

Wish everybody high rating in the last contest in this year and good holiday mood!

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    4 weeks ago, # ^ |
      Vote: I like it -28 Vote: I do not like it

    Why are wishing high rating in a not rated contest.

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

      Have you gone mad? Why couldn't you see that this is a rated contest!!! It is written clearly on the post. Stop irritating peoples with your irrelevant comments.

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

    You too!

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

    Mathematically, "everyone" can't have a rating increase :(

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

      what if everyone got the same place as their rating points rank?

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

        2 people can have the same rating but not the same rank, so it still can't happen.

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

          they can if they get same exact scored

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

            Does it matter if they have different ratings. Will rating change though?

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

      Wish everyone "non-decreasing" rating!

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        4 weeks ago, # ^ |
          Vote: I like it -34 Vote: I do not like it

        Wish everyone " increasing " rating !

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

        Wish me increasing rating! I don't care about other persons' ratings.

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

          Wish you increasing rating!

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

Happy new year codeforces !

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

Will the ratings be calculated separately for div 1 and div2 even though we are in the same contest? I feel that, unless rating changes are calculated differently, div 2 participants will be less likely to gain rating if they are in the same pool as div 1 participants.

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

    that just means div1 people gain more rating!

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +42 Vote: I do not like it

    I think otherwise. As the cf rating formula uses rank/(expected rank) as rating change coefficient, Div. 2 participant's are expected to be after div1 ones, so if they do a bit well they could get way bigger change that normal div.2. But if div1 gets beaten by few div2 people he'll farther from first place whereas expected ranks stays the same.

    PS. Out of my experience I do get biggest changes on combined rounds.

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4 weeks ago, # |
  Vote: I like it +102 Vote: I do not like it

I hope 2017 ends making me a Specialist.

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4 weeks ago, # |
  Vote: I like it +95 Vote: I do not like it

I bet for 10K+ Registrants! <3

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

    Last year there were 9.5k

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

      It will be a bigger contest! Great!

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

        we beat last year by ~300 registrants...not a huge jump but progress none the less

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

    9.8K! Missed by 200, Will be ready next year with a few fake accounts :)

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

So what's your New Year's Resolution ?

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

Are both div1 and div2 participants taken into consideration while calculating the rating change of a div2 guy?

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

Editorial right after the contest will be great, hope you will work on it.

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

If this contest goes unrated MikeMirzayanov will give 100 + rating to everyone , Happy coding guys and girls !

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

    There is no point in rating if it's not earned.

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

    Rating is just a reflexion of your brain's state.

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

      So true! Don't let just rating be the only ultimate motive of your problem solving.

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

So exciting! I still have a long way to go, hopefully 2018 will be better for me

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

How to solve D ? Update: I have mistakenly commented here. :p :p

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

Restrations.. :p 2015  2016  2017 Pending.....

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

educational round rating update and goodbye 2017 will overlap :|

PS: For the first time you can enter a round with a rating and end it with another one!

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

Probably lewin is thinking of a script such:

if(comment.writer == "metsuka"){
    GetRidOfThisComment(comment);
}

P.S. : baw bekesh biroooon!

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

LoL there is already another div2 contest in the new year!

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

Why still do not turn on New Year's magic?

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

    was looking for that comment.. it's been a while since last I saw my name in red :)

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

    maybe because it's not the new year yet

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4 weeks ago, # |
  Vote: I like it +39 Vote: I do not like it

Codeforces is reliable, as usual...

During virtual contest...

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

Considering that educational round's system-testing will happen during this contest , wouldn't it be too much of a load for the server since this contest is anyways going to have much more traffic that average?

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

    It's not your problem. Just worry if its going to be rated

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

    educational round testing will start after end of this contest. It was mentioned in it's blog.

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

Good luck everyone on the contest and in new 2018 year!

I want to believe that codeforces will have less lags in next year then in this year!

And also thanks to the guys who created an anime-contests, they was really good. I want more anime-contests in the future, does anyone else want it too?

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

Will we be able to change our handles this year?

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4 weeks ago, # |
Rev. 2   Vote: I like it +33 Vote: I do not like it

My rating changes at Good bye contest:

  • Good bye 2014: -114
  • Good bye 2015: -28
  • Good bye 2016: -71
  • Good bye 2017: -???
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    4 weeks ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    +129

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

    Starting new year with less rating doesn't feel like a good bye from 2017 :(

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it +86 Vote: I do not like it

    Your expression, that is:

    Good bye yy: yy*21.5-43382.75-(-1)^(yy)*32.25

    So, Goodbye 2017 you will get 15 increasing rating.

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

Won't the questions sorted by difficulty like in regular contests?

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

Good luck to all the participants! I hope all the participants will get high rating! Happy New Year 2018!!!

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4 weeks ago, # |
  Vote: I like it +89 Vote: I do not like it

 I guess there must be a question on tree(Christmas tree)

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    4 weeks ago, # ^ |
      Vote: I like it +63 Vote: I do not like it

    There is a comment for 2 year ago.

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

Good luck. Have fun!

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

I wonder if there are T-shirts for the well-performed?
I'm looking forward to that!

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

We are waiting for Scoring distribution

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

The contest is combined for both divisions The red contestants:

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

4500 registrations and 8.5 hours left. I think we'll have at least 8.000 participants. I hope that the site will work

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

祝大家元旦快乐!

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

Happy new year Codeforces!!!

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

scoring distribution will be 500-750-1000-1500-2250-3000-3250-3500.

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

is there any possibility to change cf handle ?

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

happy new year guys in advance and marry christmas guys <3

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

Let's hope we can see the fight between tourist and moejy0viiiiiv

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

Will magic color effect be activated this year ?

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4 weeks ago, # |
  Vote: I like it +39 Vote: I do not like it

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

Can i change my handle?

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

So, all the 8 problems are set by lewin and the others who are mentioned in the post just helped to prepare the round, not setters, right? WOW ! Great !!

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

Wish a color-change round!

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

Rush to purple or higher :)

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

    is that possible in codeforces rules? i mean going two levels up using one contest

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

      I think a lot of people jumped from candidate master straight to international master by getting around top 50 in a div1 contest.

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

Is it advisable for a contestant who gets around 1000 rank in Div2 contests to participate in combined (Div1 + Div2) rounds?

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

    It's advisable for any contestant to participate in any round.

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

    The goodbye contests are the best ever contests of codeforces ,i absolutely advice every programmer to participate in it

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

another goodbye contest , great =)

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

This is such a big contest! Feel a little nervous:)

Try my best to get a good ending of 2018.

Hope everyone will have a good ending in 2017 and get a higher rating in 2018.

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

Can every contestant get +50 without reason as a new year motivation gift? :D MikeMirzayanov

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

Open Hacking in the last EDUCATIONAL ROUND + System Test on EDUCATIONAL ROUND + Handling 10,000 participants in GOOD BYE 2017 Contest. REST IN PEACE CODEOFORCES SERVERS

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4 weeks ago, # |
Rev. 4   Vote: I like it +99 Vote: I do not like it

for CF-Predictor users:

Rating prediction for Good Bye 2017 wouldn't be as accurate as always, because previous educational round not judged yet, so div2 users that participate in it have unknown rating. I decided to use predicted ratings from educational contest as initial for Good Bye 2017.

===================================================================

Good luck & high rating and Happy New Year!

===================================================================

Предсказание рейтинга для Good Bye 2017 к сожалению будет не таким точным, как обычно, потомучто до сих не проведена финальная проверка последнего educational раунда. Таким образом у участников educational раунда (из второго дивизиона) не известный рейтинг на момент начала Good Bye 2017. Я решил, в качестве апроксимации начального рейтинга перед сегодняшним контестом взять предсказания по educational раунду. Надеюсь, что расхождение будет не очень значительным:)

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

If the sys test process is programmed to start automatically right after the educational round end, don't forget to disable it, or we will be getting 2 hours queue.

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

Can i cancel registration?

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    4 weeks ago, # ^ |
    Rev. 2   Vote: I like it -14 Vote: I do not like it

    there is no option (false statement) , but if you won't participate (do not submit anything) rating wont change.

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

    go to the contest participants list, find your name, click the red X

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

Is 2.5 hours enough for 8 problems to solve? Thanks!

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

I lost a girl recently ,so I hope I could do better in codeforces....

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

I'm anticipating a lot of math problems. Everytime lewin organizes a round, there are plenty of beautiful math problems that I always fail on :(

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

But... it's not even december 31st..

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

Hope for shorter statements :)

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

I hope it's not goodbye for 2017, but goodbye for current rate and Welcome for new Rate and new Div

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

Happy new year !!! In this 2018 I hope that we will be better than last year, and of course I wish good luck to the all contests in 2018.

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

After a long time contest=(Div1 + Div2)! :p

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4 weeks ago, # |
  Vote: I like it +131 Vote: I do not like it

CF new winner moejy0viiiiiv !!!

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

Goodbye Div 1 Contest. :|

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

are we going to see first 10k participation :D

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

well,hope i'll gain some rating.

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4 weeks ago, # |
  Vote: I like it +83 Vote: I do not like it

Waiting for around 15 minutes to post this. Have Fun

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

so this year we have 9k+ registered users for this contest. i thought maybe it will cross 10k. but nevermind, all the best guys.

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

Goodbye Candidate Master. Hello Expert. :P

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

in queue :| right before contest :|

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4 weeks ago, # |
Rev. 2   Vote: I like it +61 Vote: I do not like it

Will there be a delay to reach 10K?

UPD: as expected the first 5 mins delay :"D

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

Good luck, everyone!

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

It is Delayed to reach 10K :D

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

Have been while to see delays...

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

"you may click the link to enter the contest area"

never been so deceived in my life :(

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

Did anyone else get 0:00 on timer and contest not yet started message??

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

What will the rating change base on? My current rating or my rating after edu. round?

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

HOpE there will be no problem like site not available :/

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4 weeks ago, # |
Rev. 3   Vote: I like it -6 Vote: I do not like it

Codeforces is slow right now. :(

UPD - Seems fine now :)

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

the server is acting up again

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

dafuq is this contest :(

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

    It's all math and geometry (aka my nightmare).

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4 weeks ago, # |
Rev. 2   Vote: I like it +14 Vote: I do not like it

seems like it's DIV 1 + DIV 1.52017

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4 weeks ago, # |
Rev. 9   Vote: I like it +111 Vote: I do not like it

I hate this contest so much. First three problems are as easy as it could be, they are just stupid, not for the codeforces, and then just wtf.

I mean, usually people easily make a smooth transition from simple problems to hard problems, what the hell happened to the authors this time? There is even nothing to hack.

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

    Third one is easy if you have any idea about geometry, which I don't.

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

      If you don't know geometry, use a binary search by answer :)

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

        that gave me 3 TLE's

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

          When you do binary search on doubles, you might want to consider stopping after a certain number of steps instead of when left and right are (almost) equal. i.e. do for(int step=0; step<50; ++step) { ... } instead of while(right - left > eps) { ... }. I modified this in your code and "upgraded" it (if you can call it that) from a TL on test 4 to a WA on test 7.

          quick EDIT: I looked over your code a little bit more and fixed this line: return (one * one + two * two) < (twoR * twoR + EPS); to this: return (one * one + two * two) <= (twoR * twoR);

          ... and got accepted. (In general) Don't use eps for comparisons, only for checking equality. So in principle binary search works, you just need to know how to work with doubles :P

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

    You know what to do, do you?

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

    Arguably,I think problem A is easy for any contestant,and too easy for contestants like you,however, its level of difficulty would be equivalent to any previous A problems,but the test cases ruined the trick that many people may fail on in sense that it made the problem statement too obvious,so, problem A had a nice logical trick but it could be made more competitive than that, it was more of logical puzzle than competitive programming problem

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

    Have you read F?

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

The problem provider use Math f**k me.

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

good bye 2017, happy new year every1

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

If I submit 2 solutions and both clear the pretest will I still face a penalty of 50 points During this contest me second solution which I submitted after 4 min of the first sol my score was approximately 50 less

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

    Resubmission gets you penalty every time except compilation error or wrong answer on sample 1.

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

      even if both sol are correct and accepted? Thanks

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

        Yes. Even more: if you got accepted and then WA, your WA will be scored (I'm not sure if that's true if the WA fails pretests, but it definitely is true if both solutions passed the pretests: in that case, your last submission is considered to be your choice).

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

          ohhh.Tysm as I didn't knew about this as I am new to this platform

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

    In the score table, you can see each resubmission is -50. Only the last submission that passes pretests will be judged. Everything else will be ignored.

    So, yes, you still get a penalty.

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

    Yes, you will face a penalty of 50 points, similar thing happened with me.

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

I don't understand why my submission for 2C fails pretest#1 even though it matches the output in the problem statement :S

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

    Check your precision

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

      15 decimal points ..

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

        Check if any debugging statements are being executed.

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

          Thank you! That was it, silly debugging statements clogging the output ..

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

            Yeah happened many times with me.Try not to repeat the mistake.

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

    go to custom invocation and test the test

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

      Thanks for the tip it helped me find the problem

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

To-whoever-is-reading-this-Happy-New-Year--wish-you-the-best-this-year

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4 weeks ago, # |
  Vote: I like it +38 Vote: I do not like it

Am I alone who's hating this fucking "Expected number" ? :/

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

    I usually like this kind of problems, though, I suppose, many of contestants never solved this problems, but this time it's something beyond common sense.

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

good bye 2017 && rating

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4 weeks ago, # |
  Vote: I like it +103 Vote: I do not like it

What’s up dotorya, I am koosaga from South Korea. I’m a huge fan of you. You were 2nd in Facebook Hacker Cup 2017, your team was a Grand Champion at ICPC Daejeon 2017, you and your team continued to amaze Petr for a long time. It is unbelievable. I think your team will be a champion at ICPC WF 2018. I’m doing CP for 4 years and still I’m not like you. I want to improve my skill and be a great competitive programmer like you. How can I be a great competitive programmer like you? What is your training method?? Do you have any secret tips???? Please answer my question. Thanks in advance.

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

    (+ I was writing this 15 minutes before the contest ends, and I'm so sad that Petr got first place — no personal feelings, but it's more fun to troll dotorya when he is in first place)

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      4 weeks ago, # ^ |
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      I have same questions for you :) . How can I be a great competitive programmer like you? What is your training method?? Do you have any secret tips???? Please answer my question. Thanks in advance.

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      4 weeks ago, # ^ |
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      Yep me too(I have been recently following dotorya and he's awessome). But I was sadder before for that Petr would be losing his place for the silliest reason possible. And actually that last minute manoeuvre by Petr made the contest twice as much fun to watch.

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

        I didn't thought that he will lose his first place, but it really happened. Amazing piece of sports :D

        However, I don't know why Petr gained +250 from the Hack. AFAIK He should only gain +200. (3 * 100 — 2 * 50) (UPD : It was fixed somehow)

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

          The last hack happened 1 second after the end of the contest.

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            4 weeks ago, # ^ |
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            Yup I thought you should get +3 -2, but somehow it was written like +3 -1 (-1) and the one from 147:02 didn't count. That was what happened when I took screenshot, but it was resolved right after I wrote the reply. Sorry for the confusion :/

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            4 weeks ago, # ^ |
            Rev. 2   Vote: I like it +35 Vote: I do not like it

            for Petr even time slows down. and a black hole is created,

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          2 weeks ago, # ^ |
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          hey, can I talk to u please, ??

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4 weeks ago, # |
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What is the solution for F?

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4 weeks ago, # |
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Is F an analysis of various cases ?

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    4 weeks ago, # ^ |
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    what is test case 4 of F?!

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      4 weeks ago, # ^ |
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      test 4 is probably you need to make a cycle. something like. GRBRBRBG

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    4 weeks ago, # ^ |
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    i have a pretty simple greedy.
    Claim1: Answer is a spanning tree in most cases.(I Will describe corner case later)
    Claim2: Green component is connected by itself
    Now its pretty easy to see that after connecting Green with a chain , we need to connect reds and blues between 2 greens in a block with a chain sort of thing(We leave out the biggest gap here) Corner case (instead of connected 2 consecutive greens with a chain and reds and blues with spanning tree , we can instead make a cycle , ie connected green -> red -> red -> ... -> red -> green and green -> blue -> blue -> ... -> blue -> green).

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    4 weeks ago, # ^ |
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    Yes it is, and it is the worst type of question for a sleepy programmer to pick up in a contest. :/

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

Hack for C.

5 2
1 10 7 3 6

Output: 2.000000000 2.000000000 4.645751311 5.464101615 8.518734657

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4 weeks ago, # |
Rev. 3   Vote: I like it -39 Vote: I do not like it

edit since I've calmed down slightly

If you are going to write problems, PLEASE make sure that if you find the optimal solution, you will get the problem right instead of having to fiddle around forever with random implementation details. There is no purpose in having contestants sit around trying to reimplement standard data types or come up with increasingly "creative" (re: sketchy) ways to get around overflow or try to shave off constant factors, at least in a purportedly algorithms-based contest. Whether you implement this by increasing the time limit or setting the problems limits to something more reasonable (k=1000 is just unnecessary considering the normal Python implementation runs fine with k=500 or so) doesn't really matter, but shifting the focus away from algorithms and onto constant time improvements really defeats the purpose.

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

    I don't believe the problem is intended for you to implement fractions, but work with modular arithmetic by calculating the modular inverses by means of FLT or Euclidean algorithm.

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

      Well, official solution reimplements fraction data type, so I think this was intended. Of course modular inverses are a very easy solved problem that is used only at the end.

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        4 weeks ago, # ^ |
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        I read the solutions, and it has no mention of implementing fraction data type. What I mean by working with modular inverses is you don't ever need to work with fractions at all. Instead of a / b use and you obtain the same result, not just the last calculation. With the number of prime factors you can include as part of your input, overflow is bound to happen.

        See for yourself : 33784912

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          4 weeks ago, # ^ |
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          Ok, it is possible that I'm misreading the official solution and there is some graceful way of handling overflow. This isn't really my main point though; I don't care much about whether overflow exists supposing there is a simple way of dealing with it. My main concern/complaint is that doing this problem in Python is evidently practically impossible even with the optimal solution (there are no accepted solutions in Python), and considering that this could have been remedied with a trivial tweak to the limits (that wouldn't allow solutions of suboptimal time complexity), it seems that this was done intentionally which I cannot understand the purpose of.

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            4 weeks ago, # ^ |
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            Well then I don't understand you. The reason your Python solution probably failed is because you allowed the size of your factors to become so large they consume too much time per multiplication, addition, etc. You obviously should have evaluated the time and realised this solution is not practical. I was unaware Python does not support modulo calculations (sarcasm).

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              4 weeks ago, # ^ |
              Rev. 2   Vote: I like it -14 Vote: I do not like it

              I suppose we will have to agree to disagree then -- in my view the implementation is essentially just a means of proving one's solution, and choosing limits so that implementations in some languages are essentially not possible (at least without a lot of constant time twiddling) seems to me to place the focus off of problem solving, which in theory is what these contests aim at. But as I said, I can understand that others will have different interests and will prefer these types of constant-optimization challenges. Of course thanks for your opinion.

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                4 weeks ago, # ^ |
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                So to summarise your point, you believe big-Num multiplication is "constant time twiddling"? Because I doubt your solution fails by only a constant factor.

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    4 weeks ago, # ^ |
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    I see now official solution is to give wrong fraction but one which gives same final answer. Ok, I guess it is possible to figure out this "trick" during contest, but IMO solving the problem should be the important part of the problem and if limits are chosen so that the official solution cannot be implemented (basically word for word) in Python then something is fundamentally wrong with the writing approach. Of course I understand that everyone's taste is different and some people prefer to optimize constant factors, but IMO this isn't really what these kinds of contests are for.

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    4 weeks ago, # ^ |
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    "come up with increasingly "creative" (re: sketchy) ways to get around overflow" : that's basically half of number-theoretic problems.

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how to solve D?

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    4 weeks ago, # ^ |
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    dp on number of abs x number of as. some straightforward math needed to avoid infinite sums when num ab + num a gets to be larger than k.

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      4 weeks ago, # ^ |
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      please explain a bit more.

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        4 weeks ago, # ^ |
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        editorial explains my solution word for word basically, so just read that

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When you lock an answer and think to hack to jump up on the scoreboard, and you yourself get hacked. Crap :/ Never felt so helpless.

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So I was reading problem E and I wondered if the intended solution used any kind of knowledge on algebraic structures, did anyone solve it like that?

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How to solve H ? I have a idea based on minimum clique partition in the graph of AND-components of size

Unable to parse markup [type=CF_TEX]

, with edges corresponding to XOR constraints, but couldn't debug it in time.
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What is an 'unsuccessful open hacking attempt', showing for Petr in the scoreboard?

edit: now it doesn't show anymore

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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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    Notice that every time you place 'b' amount of subsequences "ab" increases by the current number of 'a' in the string. So dp[x][y] — answer if we have x 'a' in our string and y subsequences 'ab'. If x = 0, y = 0 then dp[x][y] = dp[x + 1][y] ('b' in the beginning of the string don't influence on the answer and we will place 'a' in one moment. The thing is that we can place many of 'a'. If x > k, then we will finish our process after first symbol 'b' will appear. So in this case we can add to dp[x][y] x + y(it will be in answer) and then add the expected amount of 'a' untill we will place 'b'. Denote the last one by E, so find it from the equation: .

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The series for G seemed very 'fractal like'. How do you solve it?

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How to solve D,E,F?

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goodbye rating 2017

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4 weeks ago, # |
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I made 9 successful hacks during the contest. Let me explain what I found...

For problem B, some implementations don't consider the last step. An example of hack is...

2 2

SE

##

0

For problem C, some consider that the intersection will occur between the droping disk and the disk with max index (and, a disk with max y). Examples to both of them...

3 10

10 30 19

5 10

10 10 50 49 30

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    4 weeks ago, # ^ |
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    Could you give the answers for your C test cases? mtkaya

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      4 weeks ago, # ^ |
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      First test: 10.0000000 10.0000000 27.8605711

      Second test: 10.0000000 30.0000000 10.0000000 29.9749844 36.2199824

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    4 weeks ago, # ^ |
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    What is the answer to the B hack case?

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Happy New Year!

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"Good Bye 2017" — last contest in CF in 2017 year — Good Bye to first contest in the next year!!.

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This Year Gift From CF " No one will lose rating from this contest " (Please) :P

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double system-test!

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first of all how the expected value for the 1st example problem of D is 2, as the expected value is 1/4(ab) + 1/8(bab) + 1/16(bbab) +.... which is 1/2. so how it came to be 2 ?

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    4 weeks ago, # ^ |
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    Don't forget sequences 'b..ba..ab', which contain number of 'a' subsequences 'ab'.

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    4 weeks ago, # ^ |
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    you also needs to multiple each of those probabilities with count of ab in them..

    for example.. aab has 2 subsequence so, it will be 2 * (1/2*1/2*1/2)

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Good Bye 2017 is fine, but where is Welcome 2018? P.S: Happy New Year :D :D

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Time to back div2. A_A

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Back to back contests with short queues and instant editorials was the only gift I received this holiday season ;)

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maths too hard~~

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Codeforces aesthetics

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Nice upvote :D

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Did anyone see anything like this when trying to hack a solution?

When will MikeMirzayanov finally understand that Flash's place is in a museum, not on a live website?