ch_egor's blog

Codeforces Round #657 (Div. 2, based on All-Russian olympiad in the name of Keldysh) [Rated]
By ch_egor, 4 weeks ago, translation, In English,

Hi!

This Sunday will take place All-Russian olympiad for students of 5-8 grades, in the name of Keldysh. Good luck to all the participants! Olympiad is conducted under the guidance of the Moscow Olympiad Scientific Committee, in particular GlebsHP, ch_egor, Endagorion, gritukan, Zlobober, _meshanya_, _kun_, voidmax, grphil and, of course, Helen Andreeva.

We are happy to announce the Codeforces Round #657 (Vintage Codeforces Round #3) based on the problems of this olympiad! It will be a Div. 2 round, which will take place at Jul/19/2020 12:00 (Moscow time). You might have already participated in rounds based on the school olympiads, prepared by Moscow Olympiad Scientific Committee (rounds 327, 342, 345, 376, 401, 433, 441, 466, 469, 507, 516, 541, 545, 567, 583, 594, 622, 626) as well as vintage rounds (rounds 626 and 628).

The problems of this olympiad were prepared by DebNatkh, grphil, KiKoS, voidmax, I_love_myself, 300iq, isaf27 under the supervision of grphil.

Thanks ch_egor, vintage_Vlad_Makeev and _meshanya_ for their help in organizing the Codeforces version of this contest and MikeMirzayanov for the Codeforces and Polygon.

Also I would like to thank the Tinkoff company and personally Tatyana TKolinkova Kolinkova for great help with organizing the competition.

Good luck!

UPD1: Scoring distribution: 500 — 750 — 1250 — 1500 — 2500 — (1500 + 1500)

UPD2: Editorial

UPD3: Winners!

Div. 2:

  1. imachug
  2. yjw0203
  3. kaixinqi
  4. penguinman
  5. FrickingFrikkie

Div. 1 + Div. 2:

  1. antontrygubO_o
  2. risujiroh
  3. tmwilliamlin168
  4. sansen
  5. LayCurse
 
 
 
 
  • Vote: I like it
  • +236
  • Vote: I do not like it

Comments Comments (467)
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3 weeks ago, # |
  Vote: I like it +11 Vote: I do not like it

Number of problems?

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3 weeks ago, # |
← Rev. 2   Vote: I like it -86 Vote: I do not like it

im-back.jpg

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    3 weeks ago, # ^ |
    ← Rev. 2   Vote: I like it -69 Vote: I do not like it

    You can not call it back , until it finish !

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      3 weeks ago, # ^ |
      ← Rev. 2   Vote: I like it -46 Vote: I do not like it

      Yeah.. until then lets hope for one! :-)

      P.S. I don't understand why my comments are getting so much downvotes. I am only trying to maintain harmony. :-(

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3 weeks ago, # |
  Vote: I like it -46 Vote: I do not like it

I am excited to see problems of Russian olympiad

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3 weeks ago, # |
← Rev. 2   Vote: I like it -138 Vote: I do not like it

.

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3 weeks ago, # |
← Rev. 4   Vote: I like it -61 Vote: I do not like it

[DELETED]

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3 weeks ago, # |
← Rev. 2   Vote: I like it -57 Vote: I do not like it

.

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3 weeks ago, # |
  Vote: I like it +177 Vote: I do not like it

The last time I saw these many reds was when I witnessed an accident.

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3 weeks ago, # |
  Vote: I like it +35 Vote: I do not like it

What are vintage rounds?

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3 weeks ago, # |
  Vote: I like it -9 Vote: I do not like it

Can I be BLUE....

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3 weeks ago, # |
  Vote: I like it +737 Vote: I do not like it

No offence to anyone

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

    So true!

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

    Damn true. Even the school kids will solve till F and we would be struggling with C and D XD

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    3 weeks ago, # ^ |
      Vote: I like it +66 Vote: I do not like it

    Well I take offense

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

      Some big aim you had in your first year! Most desi Indians only think about hacking Facebook when starting in CS :P

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

    Our education system needs improvement, If I would have started coding from my 5th grade then I think I would have been red coder till now, and I beleve its true for all Indians.

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      3 weeks ago, # ^ |
      ← Rev. 2   Vote: I like it -21 Vote: I do not like it

      Nah ! If i ask a random 5th grade Indian student to start cp ,he/she would not be even be excited or motivated about it. Exceptions do exist but i am talking with respect to general population . I was more interested in playing football and cricket at that age .

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

        but what they taught in schools can be changed to what we want to be taught depending upon your interests which will eventually help us in future

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

        Even I was more interested in playing cricket, but I do wonder if I got introduced to CP I may have latched on to it because I had a good interest in maths and aptitude at that age and also CP has a gaming front to it with all the rankings and points, you just need a given the proper introduction and some good peers to compete with :)

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

      Yeah many of us feel the same, but no probs curently CP is rapidly evolving in India. India will have good number of GM's after a decade or so. And we need to create awareness about CP for a 5th grade student.

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

      I remember learning paint in 5th grade in school lol

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

      If coding from (5th grade -> today) = red coder then coding from (today -> today + 10 years) = red coder too. On top of that at this stage one will need much lesser time maybe 4-5 good years is enough.

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

    The same happens in Peru, but with the 5th semester students. From the 1st to 4th semester they just use microsoft excel.

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

    I wanted to code when I was a kid but didn't know where to start

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

    Logged in, only to upvote you.

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

    Our tradition is to memorize maths to pass exams.

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

    Would gladly take this over 70 years of communism.

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

    So hard to accept our education system

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

      you can't blame it on education system ..... NO

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    3 weeks ago, # ^ |
      Vote: I like it +31 Vote: I do not like it

    If this contest was for 5-8 grade students, I feel like I am a new born baby.

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

      This contest for 5-8 grade students and I couldn't solve any question. Seems like I dont know cp.

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

    Can feel this bro :')

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3 weeks ago, # |
← Rev. 2   Vote: I like it -37 Vote: I do not like it

Schools are like:

  • Taught in Class: Div2 A

  • Solved for practice: Div2 B

  • Homework: Div2 C

  • Exams: Div2 D,E,F

credits: adzo261

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

why is that unusual time ?

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

    Because problems took from olympiad and for prevent leaking it, round will be in the same time as olympiad

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3 weeks ago, # |
← Rev. 2   Vote: I like it -28 Vote: I do not like it

It is rated.ok

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3 weeks ago, # |
  Vote: I like it -40 Vote: I do not like it

Is it rated?

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

me in 8th grader : tell my friend to open page 69th of biology book where there is a picture of penis anatomy
russians 8th grader : solve div2 problems

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

Will the round be rated ch_egor? Asking because its not stated in the blog post:)

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

great !! we have 300iq now ... I am excited !!

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3 weeks ago, # |
← Rev. 2   Vote: I like it -6 Vote: I do not like it

m

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

That's a lot of red handles

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

Why are there so many down-voted comments in this blog?

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

(Notice the unusual timing)

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

I think people should think before voting because even the comments which are not at all negative are downvoted heavily.

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

Please do the contest later, in Central America it is 3 am

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

we will b enjoying this contest

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

This is 5 AM in America where I live

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

    Considering the lockdown, does the time even mean anything anymore?

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

      Yes, there's something called body clock, which when affected can cause various health problems

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

Score Distribution?

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

As per IST, I have Leetcode weekly (08:00) Cf div 2 (14:30) Codechef Cook off (21:30) Best weekend ever :) !!

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

Any reason why start time is 09:00 UTC, but not 09:05

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

    Probably because it's going to be held in parallel with All-Russian olympiad. Also to avoid clash with Topcoder and Codechef rounds.

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

Hope the problem statements are clear and interesting xD

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

hey !

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

How many problems and Score Distribution?

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3 weeks ago, # |
  Vote: I like it +111 Vote: I do not like it

Unfortunately, the last 6 months we have seen this instead of the exciting confrontation between tourist and MiFaFaOvO :)

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

    Nice!!!

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

    Rating: users participated in recent 6 months

    Since his last contest was on Feb 17, either he'll take part in another contest or disappear from the global rating in a month.

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

    At least he's visiting the site which means he is still alive. :)

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

where's Vovuh ????? :-(

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

I am expecting a lot of math problems, hope that I am wrong

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

Never mind. :)

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3 weeks ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

What's the Score Distribution? ch_egor

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

No Score Distribution and No. of Problems yet? ch_egor

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3 weeks ago, # |
  Vote: I like it +84 Vote: I do not like it

where scoring distribution and number of problems will be published?? ch_egor

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

Scoring distribution says it's gonna be SpeedForces.

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

the first round during my summer vacation lol

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

I'm sure some people will join 5 minutes late thinking that round will start at 14:35 IST. :v

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

I am not able to find "register" button...

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

Is this Div1?

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

    Seems so! Not able to TOUCH a question!!

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

      I think we really need the help of pavan putra hanuman to solve the questions in this contest Xd.

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3 weeks ago, # |
  Vote: I like it +81 Vote: I do not like it

There has been a small typo guys.. it is a Div 1 round..

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3 weeks ago, # |
  Vote: I like it +44 Vote: I do not like it

one hand pushups were easier for me than this round's problems!

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3 weeks ago, # |
  Vote: I like it +50 Vote: I do not like it

I've never seen such DIV 2 contest.

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3 weeks ago, # |
  Vote: I like it +45 Vote: I do not like it

Now I get why Russians dominate in competitive programming. :)

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3 weeks ago, # |
  Vote: I like it +82 Vote: I do not like it

This is for 5th-8th grades?? OKK

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

I wasn't able to enter codeforces for almost 20 minutes. Anyone else facing the same issue?

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

Should have rather rushed Bombsite B. On a serious note, is this really what 7th Grade Russians study? That is really impressive, no wonder Russians are such good coders.

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

Great div1 round!!!!!!!!!

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

2 minutes silence for all those who were too eager for the round to be rated.

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3 weeks ago, # |
  Vote: I like it +31 Vote: I do not like it

After walking through first 3 question:

How to unregister???

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

OK now I'm looking forward to the editorial after the contest.

I'm feeling numb :( Is it a Div.2 round or Div.1 Round?

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

    Round by Red round for Red . Screaming Red.

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

    Lul bruh, I have the exact same pattern of submissions, except I'll become specialist by today evening.

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

This is meant for students of grades 5-8? Wow.

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3 weeks ago, # |
← Rev. 3   Vote: I like it +1 Vote: I do not like it

worst div2 i ever seen !!

upd: I said worst cause its seems more div1 than div2 but named div2.

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

is this round rated??

plz reply

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3 weeks ago, # |
  Vote: I like it +64 Vote: I do not like it

I am proud that I have participated in Div 1 round.

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

I was getting 504 server error during first 20 minutes. I am feeling blessed.

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

    Are you the lucky one?

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

    I was having the same issue for a very long time. I think this happened with many people and not just a few of us. There were more than 15k people who registered and on the scoreboard there are only 8000 who have attempted a single problem.

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

      I think this could have been because it was very early morning in the US, so lots registered but not many woke up that early.

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

    You can always use these lightweight websites m1.codeforces.com m2.codeforces.com m3.codeforces.com in such trouble of server in my case these websites work almost everytime in a live contest.

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

    glad to hear it wasn't only me xD

    I was afraid I was the only one

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

feels like DIV1 to me

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

New technique to manage server load.

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3 weeks ago, # |
  Vote: I like it +175 Vote: I do not like it

This is Div 1 :(

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

Are you trying to kill those poor 5-8 graders ?

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

    They might have completed the problemset by now. Russian kids are seriously genious.

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

No wonder why tourist is so perfect.

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3 weeks ago, # |
  Vote: I like it +41 Vote: I do not like it

is there any way to undo submission?

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

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

Ah, it was good that my connection was lost during the first 30 minutes.

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3 weeks ago, # |
  Vote: I like it +91 Vote: I do not like it

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3 weeks ago, # |
  Vote: I like it +105 Vote: I do not like it

When you realize that this was actually a Div. 1 contest

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

Hell lot difficult contest!

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

Was this div 2? this was Div 1 ! Even more difficult , Div 0 maybe

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

I registered for the contest, I planned to participate in it, but I slept and couldn't wakeup on time. I was feeling bad but then i read the problems and number of submissions. Thank god, i didn't wake up on time! xD

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

You miss 100 percent of the shots you don't take.

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

why there is no extra registration?

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

    so that no one else falls into this trap

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

this is my first ever contest....I havent even solved a single question

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

Codeforces Round #657 (Div. 1, based on All-Russian olympiad in the name of Keldysh) [Rated] .. Looks better Now :)

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

Can I see how many problems those 5th-8th graders solved? Might be a motivation for me or myth buster for many!!

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

Before reading the comments I thought I don't deserve to be yellow on CF...

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

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

The the last four div2 contests (excluding the Global round):

654 — widely disliked

655 — good set but queueforces

91Edu — good set but major crash

657 — Mere mortals can't solve more than 2

(I agree I'm not of high enough calibre to say all of this but damn it a man needs to vent — I've been at 1750 for 10 contests and I couldn't solve a single one — damn pretests 2)

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

    Try to concentrate more on developing problem solving skills than on rating.

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

    Finally, I found you another expert, that did 0. And you have a much higher rating than me. I am sorry but I feel better now. ;_;

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

    A hint : abacab*bacaba needs to Output "NO"

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3 weeks ago, # |
← Rev. 4   Vote: I like it +60 Vote: I do not like it

Me after not being able to solve a single problem

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

couldn't solve a single problem :(

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

Russian 5-8 Grade students solving this... **Meanwhile Final Year graduates in India- I can Hack Facebook in 2 mins.

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3 weeks ago, # |
  Vote: I like it +46 Vote: I do not like it

My son was in 8 grade, Now I don't have a son...

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

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

So much implementation :(

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

Div 0 round

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

What is wrong with my A:87342260

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

    1 11 abac???caba, answer should be no as they want "abacaba" exactly once

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

      You are right, Thanks for the test. Does that mean that I just need to add some cases to my code? Or I will code another solution

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

What is the third testcase for C?

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

It's a record. First time 20k participant in div — 1 round.

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3 weeks ago, # |
  Vote: I like it +181 Vote: I do not like it

New technique to manage server Load

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

How to solve C?

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

    We will only buy more than one flowers of only one type iterate to choose this and greedily take other flowers who have ai >= chosen bi

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

      I tried to do like this but it hasn't worked(

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      3 weeks ago, # ^ |
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      I tried similar approach but couldn't get past test 5. What did you fix to pass that?

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        3 weeks ago, # ^ |
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        I didn't consider if no ai > chosen b

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          3 weeks ago, # ^ |
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          I did that too at the end, still failed :( Guess something is wrong with my implementation. Thanks.

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          3 weeks ago, # ^ |
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          Oh I found my mistake, I didn't handle this case: Number of Ai >= b is already >= n, in that case, I shouldn't take this b.

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      3 weeks ago, # ^ |
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      my idea was similar but I implemented it wrongly I guess. Thanks for replying.

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      3 weeks ago, # ^ |
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      I did the same and got WA2 T_T

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3 weeks ago, # |
← Rev. 2   Vote: I like it +8 Vote: I do not like it

Probably it was the hardest was the A ever

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

I don't see why is it rated for me when I'm clearly not a div1 participant

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3 weeks ago, # |
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How the hell those russian kids are solving? I am feeling like idiot.

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

any hint for problem C !

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

    you knew that you should take a[i] at least once to take b[i]. so, first sort all array A, then if we take a[i] once, then we have two options in the next step. take a[i + 1] or (b[i] for all remaining flowers), so think where you will know that you will take b[i] for all remaining flowers. i think this enough as hint. if u wanna more hint or there is anything ambiguous , tell me.

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3 weeks ago, # |
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What's tc18 for F1?

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3 weeks ago, # |
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It is kind of funny I visit the CF blogs comment section to see memes.

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

this contest is for grade 5 to 8,OMG i can only imagine level of Russian kids

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

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3 weeks ago, # |
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Problem A is not as easy as I though, it actually requires more implementation than usual :)

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3 weeks ago, # |
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How to solve C? I tried a greedy strategy but it is not always optimal, and I believe fixing it would require m^2.

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    3 weeks ago, # ^ |
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    Why greedy is not always optimal?

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    3 weeks ago, # ^ |
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    I think it is something related to convex hull optimization technique.

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      3 weeks ago, # ^ |
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      I don't think so! I believe, greedy will work! Even though, I couldn't reach up to a correct solution.

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

    Notice that you will only take b_i of one type in the entire process (if you could improve the answer by taking another b_k, you would just take all b_k as it would be better), and that it is optimal to take all a_j >= to this b_i before taking it and that you must take a_i before you can take b_i.

    Now you can just iterate over b_i in descending order and do something like two pointer to keep track of the sum of a_j >= b_i taken while maintaining a used array to see if you've taken a_i already when taking b_i, so answer will be max of (asum till now + (n — a_taken) * b[i]), minus b[i] plus a[i] if we haven't used it yet.

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

      I tried same thing. But, might have missed out something in the implementation! :(

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        3 weeks ago, # ^ |
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        Did you clear the used array? I got 2 WAs and wasted 10-15 mins thanks to that

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          3 weeks ago, # ^ |
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          Actually, I used 2 PQ's to implement this. Maybe, I missed something in the casework.

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      3 weeks ago, # ^ |
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      Ahh I see. I tried to implement it backwards (iterate over all a_i in descending order and find the best candidate for b, which I thought was O(1) since you can keep track of the max b already taken and not already taken, but the max is not always optimal. Nice solution!

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

It seems Div1 round for Div2 participants. Too Hard! ToT

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3 weeks ago, # |
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Counter case for taking times modulo m / 2 (and ignoring hours), sorting and finding largest range with distance of max m / 2 — k using two pointer in D?

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

    I kind of did the same thing. My solution was failing on this-
    4 24 4 2
    16 0
    17 1
    18 2
    19 3

    Try this

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

"Wrong answer on pretest 2"

5 words which summarize the contest

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3 weeks ago, # |
  Vote: I like it +35 Vote: I do not like it

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

Seems like old codeforces rounds are back. Kudos to the author , Nice educational problemset. I hope more of such rounds which teaches how to solve real algorithmic problems in future, A B C were absolutely fabulous and not as per the score given to them , B is much more worthy than 1000 also. Again Thank You for such a brilliant round.<3

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    3 weeks ago, # ^ |
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    Yes true many people will complain about how bad the round was just because it was hard but the truth is it was really educational as even the implementation was hard and required debugging skills and the problems logic was also good.

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      3 weeks ago, # ^ |
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      Specialists are dumb

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        3 weeks ago, # ^ |
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        Please have a look at my graph before making assumption :P

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      3 weeks ago, # ^ |
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      yeaheverybody is crying but it was quite a challenging round and a nice change

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

Okay, Dear problemsetter,

No matter what you gonna say or not,you must agree on the fact that these problems was rarely similar to div-2 problem format.

Totally disappointed. I know I am not capable enough,but still I am gonna say,this contest was the hardest contest in recent time. It was not for div-2 at all.

Thank you.

No offense.

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

Should I register for next DIV2 round or not?

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

    Never fear for ratings always assume that they are a sideffect of Leaninig. If losing rating hurts you then also its normal try not looking at standings during the contest and also not at all look at your colour, just believe that giving contest and one like this is making you a learn something new, everyday. and also training you on what you already have learnt. Especially do all those contests given in a list combined in the announcement above. These are some of nowadays rare contest problemsets and amazing. Once again do register and solve problems for fun.

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

My First Div 1 contest done !! -_-

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3 weeks ago, # |
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This contest was harder than usual but problem were really interesting!

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3 weeks ago, # |
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Can someone give a hint for D? Is it a ternary search?

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3 weeks ago, # |
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can anyone tell me what is wrong in this solution?? https://ideone.com/rajqqD. This solution is for Acacius and String.

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    3 weeks ago, # ^ |
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    Buddy submissions won't be visible for 1st hour after the contest(check the announcement) better paste your formatted code here

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

All these comments and the round is still running? seriously guys!!!

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    3 weeks ago, # ^ |
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    what?

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    3 weeks ago, # ^ |
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    I think people didn't have anything else to do.

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      3 weeks ago, # ^ |
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      OK I understand the problems were harder than usual ( and much more interesting :D ) but admins should shout down comments during the contest, what if someone talks about his solution for one of the problems!!!

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3 weeks ago, # |
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How to solve B?

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    3 weeks ago, # ^ |
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    Nvm

    Didn't understand the statement completely

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    3 weeks ago, # ^ |
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    Fix a and then try to find b, c.

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      3 weeks ago, # ^ |
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      did same still WA.

      My code
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        3 weeks ago, # ^ |
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        Actually you should check for both $$$rem = m$$$ % $$$a$$$ and $$$rem = (m + a - 1)$$$ % $$$a$$$

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    3 weeks ago, # ^ |
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    You have $$$n*a + b - c = m => n*a = m + x$$$ where $$$ x = c-b $$$ and $$$ m+x \in [-maxr+m,m+maxr]$$$ where $$$maxr = r-l$$$ Iterate over a and do a binary search over $$$n$$$ and check if $$$n*a \in [-maxr+m,m+maxr]$$$

    So if you have $$$n$$$ and $$$a$$$ you can simply fix $$$b = l$$$ and calculate $$$c$$$.

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      3 weeks ago, # ^ |
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      No need for binary search, just find closest values to m you can get by taking positive amounts of a using division.

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3 weeks ago, # |
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solved 0 questions but still a good round

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3 weeks ago, # |
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Thanks for the great contest.

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3 weeks ago, # |
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Too difficult for me...fighting!!!!

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3 weeks ago, # |
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What is wrong in this code: Todays: B

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

For problem D, I think the hour value of trains wasn't necessary.
Was it supposed to be solved by iterating on all "minute" values of trains as a candidate of $$$t$$$ and then finding how many minute values intersect the range $$$[t-k+1, t-1]$$$?
Ofcourse, this will have few cases to consider like $$$k=1$$$ or $$$t<k$$$ but was this the overall idea for D?

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3 weeks ago, # |
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is it just me?? the codeforces were saying "can't connect right now" by the time contest was starting and after 5 or so minutes later it started. I submitted my C problem solution before 2 minutes but it keeps loading and loading after the contest I checked whether it submitted or not. But it wasn't submitted?

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3 weeks ago, # |
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People before contest were asking — how many problems? Meanwhile ch_egor to himself : Actually there are two problems.

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3 weeks ago, # |
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How to solve C ? is there a greedy approach to it?

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    3 weeks ago, # ^ |
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    optimal flowers choice is to take some flowers only once, and then take one flower and put it to the rest of the slots in bouquet.

    you have to iterate through that flower which is gonna be put to the rest of the slots and update the answer.

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3 weeks ago, # |
  Vote: I like it +28 Vote: I do not like it

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

Can anyone from Russia covert 5-8 grades to the equivalent level of American or Indian Education system, or at least tell me students of what age group study in Grade 5-8 in Russia?

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3 weeks ago, # |
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Problem B seems easier than Problem A.

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

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3 weeks ago, # |
  Vote: I like it +48 Vote: I do not like it

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

I misread the contest as DIV-2 and registered it. I didn't knew it was DIV-1

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3 weeks ago, # |
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why my B solution is wrong?

:(
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    3 weeks ago, # ^ |
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    same w me :))

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    3 weeks ago, # ^ |
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    There are some cases that n*a have to be above m

    In this case for example

    7 8 13

    the answer will be

    7 7 8 , where n = 2 and 2 * 7 > 13

    and the m%i method won't work for these cases.

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

try this test case if you are getting WA on pretest 2, problem A.

1
12
abacab?cabac
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    3 weeks ago, # ^ |
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    My code says "NO", and I was still getting WA on pretest 2

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

      Try this test case for problem A

      1

      11

      ???????caba

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        3 weeks ago, # ^ |
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        ah this is the test case that got me... thank you