Ari's blog

Codeforces Global Round 9
By Ari, 4 years ago, In English

Hi!

On Jul/04/2020 17:45 (Moscow time) we will host Codeforces Global Round 9.

It is the third round of a 2020 series of Codeforces Global Rounds. The rounds are open and rated for everybody.

The prizes for this round:

  • 30 best participants get a t-shirt.
  • 20 t-shirts are randomly distributed among those with ranks between 31 and 500, inclusive.

The prizes for the 6-round series in 2020:

  • In each round top-100 participants get points according to the table.
  • The final result for each participant is equal to the sum of points he gets in the four rounds he placed the highest.
  • The best 20 participants over all series get sweatshirts and place certificates.

Thanks to XTX, which in 2020 supported the global rounds initiative!

The problems of this round were prepared by a team of authors: adamant, antontrygubO_o, Ari, dengyaotriangle, hugopm, Kuroni, enoone, and Ynoi. We would like to thank the following people:

You will be given 2 hours and 30 minutes to solve 9 problems, and we highly encourage you to read all of them :)

To save testers the work of writing their opinion in the comments, we have compiled some of their opinions for them!

Round Feedback

Good luck!

UPD: Score distribution:

500 — 750 — 1500 — 1750 — 2000 — 2000 — 2250 — 2750 — 4000

UPD2: Editorial

UPD3: System tests have finished, congratulations to the winners!

  1. tourist
  2. scott_wu
  3. yosupo
  4. Um_nik
  5. Rewinding
  6. lqs2015
  7. heno239
  8. Motarack
  9. zeronumber
  10. Itst_boyfriend
Announcement of Codeforces Global Round 9
  • Vote: I like it
  • +2693
  • Vote: I do not like it

Comments Comments (449)
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4 years ago, # |
  Vote: I like it +3388 Vote: I do not like it

As a tester, give me contribution.

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    4 years ago, # ^ |
      Vote: I like it +49 Vote: I do not like it

    You are so honest. Otherwise, most of time tester tries to gain contributions by just commenting something shit....

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    4 years ago, # ^ |
      Vote: I like it +177 Vote: I do not like it

    The only thing I remember about Monogon is that his first ever contest after being such a beauty was ruined due to long queues and finally the round became unrated. Awaiting another round from you.

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

    ok

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it -16 Vote: I do not like it

    Sorry for that..

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

    You are now in top 10 contributors. Cong!!

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

    may be for the first time a tester is going to get more contribution than the setter xd
    need 247 more only :P

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

    The most upvoted comment ever?

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

    If only herd immunity was as easy as herd behaviour...... P.S. you have my vote.....

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

    I hope Monogon prepares a round after gaining such support from the community. We will try to make the contest announcement blog the most upvoted blog on CF.

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

    You have it, >2000 upvotes :D.

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    4 years ago, # ^ |
      Vote: I like it +251 Vote: I do not like it

    As the most upvoted comment in history, I think this proves that the greedy works.

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

    Damn! Even, most of the "contest announcement" blogs have less upvotes.

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

    Would it break the tourist's global round 5 record?

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

    This has to be a record of some kind.

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

    Can monogon's comment beat tourist's rating someday? =O

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

AC Round #3

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

    What is AC Round ?

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

      AC is a discord server for competitive programmers. Most of the authors/testers of this round are members of the server. This is the third round made by AC members, here and here are the first two rounds.

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4 years ago, # |
  Vote: I like it +208 Vote: I do not like it

This has to be one of the best contest announcement.

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

I am not tester, but i strictly reccomend you to participate in this contest!

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4 years ago, # |
  Vote: I like it -60 Vote: I do not like it

I'm a tester, and this round is very good.

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it -8 Vote: I do not like it

    Why am I getting downvoted? I'm stating my opinions as a tester.

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

      Cause everyone saw that, you are not in the tester list :v

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4 years ago, # |
  Vote: I like it +119 Vote: I do not like it

As a participant, I need more time to recover from the previous contest.

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4 years ago, # |
  Vote: I like it +304 Vote: I do not like it

They stole my contribution =(.

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

Ok then

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

very comedically humorous Ari

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

Is feedback meant for frightening us?

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4 years ago, # |
  Vote: I like it +48 Vote: I do not like it

As a participant, I am already scared

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4 years ago, # |
← Rev. 2   Vote: I like it +204 Vote: I do not like it

Finally this day has came, a round with adamant as an author.

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

thanks for the meme!

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

The announcement just ensured that one more time we are gonna miss MiFaFaOvO vs tourist match.

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

    Tbh, it looks more like ecnerwala vs tourist to me. Just an opinion tho.

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

      I don't get why you guys are more interested in tourist than yourself.

      Is that why you are green/cyan?

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

        I find inspirations seeing the success of some great coders so that i am interested about them.You better focus on your own success (as you are a colorless or a fake account).

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

Glad a real CF round is coming,last round killed my spirit...

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

    Hope this doesn't happen

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

      .

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

        Do you want to say anthing about this

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

          Yes I wasted a lot of time and truly it sucks . Moreover it made me realized that I should focus on solving problems instead of making memes. I had no intention of disrespecting you but only making letting you know about my mistake.

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

            Thanks for letting me know. I had no intention of disrespecting you too.

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

As a participant, I am eager for tourist vs Um-Nik

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

    That's rather as a spectator. You don't need to participate for that.

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

tags: "doomsday" oof

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

People trying to be sarcastic in comment section Problem Setters And Testers : Say No More

Ps : Is it best announcement ever? :P

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4 years ago, # |
  Vote: I like it +116 Vote: I do not like it

jqdai0815 : " I'm happy sitting atop the CF rankings. You guys give the contest."

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4 years ago, # |
← Rev. 3   Vote: I like it +69 Vote: I do not like it

You will be given 2 hours and 30 minutes to solve 9 problems, and we highly encourage you to read all of them :)

Is this statement meaningful or is this general good advice for any round?

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4 years ago, # |
  Vote: I like it +139 Vote: I do not like it

But man, by the time I understand 9 problem statements, 2,5 hour is already gone, and I already forgot 8 of them...

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

As a russian guy, I don't understand tester's feedback.

Joke

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

Looks like it's going to be a difficult contest.

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4 years ago, # |
  Vote: I like it +220 Vote: I do not like it

"As a problemsetter, I am sorry"
As a contestant,

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4 years ago, # |
  Vote: I like it +256 Vote: I do not like it

......

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

As a participant, I will participate.

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

Looking forward to the problems. The announcement is hilarious and I hope the problems will be as well.

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4 years ago, # |
  Vote: I like it +235 Vote: I do not like it

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4 years ago, # |
← Rev. 2   Vote: I like it +21 Vote: I do not like it

Don't worry, you guys are gonna enjoy the round :)

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

Probably, one of the best contest announcements.

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

As a contestant, I quit.

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

i'm confused, should we be playing or not?

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4 years ago, # |
  Vote: I like it +185 Vote: I do not like it

I see that I'm going to love this round...

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

    No, you'll say that there is another platform for such contests

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      4 years ago, # ^ |
        Vote: I like it +106 Vote: I do not like it

      To be honest, adamant and antontrygubO_o together as problemsetters give hope that we'll finally see some balance.

      But also the opposite is possible: that every problemsetter has just a position (A-I) assigned and all the problems will be chosen completely independently from the others and we'll finish having a 100% "another platform" contest.

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

Hoping to become an Expert after this round :)

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4 years ago, # |
  Vote: I like it +441 Vote: I do not like it

Do you want to get fewer participants with this anti-advertising of the problem set? If the goal is to avoid the server load, just say that there will be a lot of math in div2 problems.

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

    LOL ! People will still try out of courage and for rating ! If it goes well they will be commenting like Best ProblemSet ever ! and if not they have their cliche MathForces

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    4 years ago, # ^ |
      Vote: I like it +431 Vote: I do not like it

    There are a lot of math in div2 problems.

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

    Errichto It's been a long time since we saw you setting problems ! Come Back ! Soon ! :)

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    4 years ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    Even better, just say the whole round is Geometry

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it -16 Vote: I do not like it

    When you khow people scared with math then do you do something like tutorial on how to get well in math? Errichto

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

      I doubt that abundance of tutorials is going to cure aversion to "math".

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

    I think. they r going for reverse psychology here....!!

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

First time, I see meme in contest announcement.There must be a reason behind it. We should be aware of that.Good luck to everyone. :p

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

How pupils become tester? :D

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

As a contestent, I want rating.

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

xd

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

Same story, again and again, my smoll pp skills and big pp problems.

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

Best CF Round invitation ever =P

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

as a participant, i am also scared and i don't want to participate!)

GL&HF to everyone!!!

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

....

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

    As a tester, My advice is to think 1 more day, because problems are more scarier than you are thinking...XD

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

I don't know why but it is giving me vibes of an amazing round.

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4 years ago, # |
  Vote: I like it +167 Vote: I do not like it

.PicsArt_07-02-02.16.38.jpg****

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

9 Problems with an army of testers and 8 writers. Excited

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

IT IS TAGGED DOOMSDAY!!!

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

New here, it is going be my first Global Round and the comments already scare me. Is it a good idea for a new guy to take part in it? or will it be discouraging?

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

    If you are new dont think of rating from the beginning try giving as many contest as you can. Thats what i learnt

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

9 problem that's huge. I appreciate the hard work to make a contest.

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

    Yes appreciate problem setters for these kind of contests

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      4 years ago, # ^ |
        Vote: I like it +41 Vote: I do not like it

      "You will be given 2 hours and 30 minutes to read all of them." I think that's what he is trying to say.

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

Links of previous global rounds:

Codeforces Global Round 5

Codeforces Global Round 6

Codeforces Global Round 7

Codeforces Global Round 8

Hope this helps!

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

    Appreciate your work but we can directly search any round and go to contest link in the announcement.

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

      The reason why it is not useful is probably not that "we can find it ourselves" but that this list was also shared in the previous global round. In fact, link to a web app was shared which can do this right away.

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

This global round seems to be very special among all previous global rounds because of its awesome announcement!!

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

I was going to make a century of losing rating in last contest...I think,this is another opportunity to complete the century...Shouldn't I be happy!!! SENTY_EMO

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

how is global round different from other rounds???

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

As a contestant, I will take part in the contest. :)

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

Can someone tell me what happened to static a2oj? I used to solve problems from there difficulty wise and now, instead of that a different website with that names comes and all the problems of the ladder are locked there.

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

Finally, memes are on Contest announcement blog post :v

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

Explain me the difference between Educational round and Global round in div 2 like contest there is time penalty what about Codeforces Global Round .Thank you.

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

    In Global round also every problem score decrease with time . It's almost like Div-2.

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

    1. Global round is rated for everyone, educational round is rated for people who have rating less than 2100

    2. Global round has some fixed points for each problem which reduces slowly as time goes on, all problem has equal points on educational rounds.

    3. Hacking runs parallel with contest in global round, there is hacking phase in educational rounds after contest finished.

    4. Wrong submission on finally accepted solutions will cost you 20 points in global round, in educational rounds it will cost you additional 10 minutes time penalty.

    5. On global round last pretest passed solution will be judged and resubmission will cost you 50 point and in educational rounds all pretest passed(accepted) solution will be judged and 1st solution that passed system test will be considered.

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

      How do you compare 20 points vs 10 minutes of penalty? What is the exact relation (if there exists one)?

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

        I compare in sense of what will happen one submit a wrong solution.

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

thanks to all of them for frequent rounds

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

Next round after the global round is one week later.Are we not going to have any round before that?

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

    There are almost 2 educational and div3 rounds in every month.So probably we will be having both also if a contest is added for date x it does not mean mike can not add a contest which has date strictly lesser than x.

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

A meme in the announcement .. you got my upvote

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

    Hey Boss how to get like your meme idea.. I want to make my contribution 0.

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

      the idea just flashes in my mind and I search for photos that can present the meme and edit it on paint
      I can give you an advice some of my memes goes this way you just compare 2 completely opposite situations like this one
      it's how I used to be when I started and how I'm like now this meme is actually sad for me XD
      or like this one
      it starts with someone asking them to be quite while it ends up with a party so there should be an element of surprise if it's something expected or usual then this is a bad boring meme and it should be about codeforces and competitive programming not jokes about html that's out of the context

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4 years ago, # |
  Vote: I like it +179 Vote: I do not like it

You will be given 2 hours and 30 minutes to solve 9 problems, and we highly encourage you to read all of them :)

Problem I.

You are given two integers a and b. Print a+b.

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

I am excited for the round..hope for the best

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

dude that feedback gave me chill more than any meme xD xD

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

WTH to me. i was going to attend the contest today at 20:35..

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4 years ago, # |
  Vote: I like it +87 Vote: I do not like it

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

I like this meme!

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

I love the announcement """""D

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4 years ago, # |
  Vote: I like it -48 Vote: I do not like it

In problem B,can anyone explain this formula => a+(a+1)+(a+2)+...+b=(a+b)∗(b−a+1)/2 and what is it called

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

I hope there are a few or no problems based only on observation

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

    I hope a problemset like that of the previous round doesn't happen again. Problems A-D: Observation. A-C are 1 liners. D is two nested for loops which can be written with 3 lines. Problem F: Think for half a second, implement for half an hour.

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

In China, there is a well-known serie of huge datastructure problems called Ynoi.... Is it gonna have huge datastructures like ctholly tree?

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

As a stupid American, I don't get the testers' jokes.

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4 years ago, # |
  Vote: I like it -21 Vote: I do not like it

As a participant, I have a hunch that I should hide my brain during the contest

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

Excuse me. Can someone tell me how the round is rated? I mean: is it rated like div.1, div.2, or div.3? I'm not very familiar with the contests of CodeForces (as you can see I'm a Newbie). Thanks for helping!

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    4 years ago, # ^ |
    ← Rev. 3   Vote: I like it -20 Vote: I do not like it 
    Sorry for wrong...
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      4 years ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Alright. Actually I thought that it is rated in a way like div... but it seems that it's different. Thanks anyway.

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

so here comes the DOOMSday

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

For the first time, I am feeling nervous that something bad is going to happen with me in this round :(

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

    and what are the good things that happened to you in any round till now

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

Codeforces contests are like a sport for me . I enjoy the problem mostly without noticing my rating .

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

is this one as easy as div 2?

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4 years ago, # |
  Vote: I like it -74 Vote: I do not like it

tourist after reading round feedback

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

As a participant, I am scared.

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

how the contribution is calculated.

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

    It works like the hippos, you have to effectively shed your territory.

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4 years ago, # |
← Rev. 2   Vote: I like it +64 Vote: I do not like it

Ari Hey, I understand that you want to make a point, but don't you think tagging them is unnecessary? I believe noone likes to be tagged just to see themself being thanked every week.

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

GOOD LUCK TO EVERYONE!!!

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

Out of curiosity, What's the record for the most downvotes? (Can this comment break that record? xD)

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4 years ago, # |
  Vote: I like it +149 Vote: I do not like it

gamegame and dorijanlendvaj, for their help in improving the humor of the round.

During round :

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

Honestly, Is this contest suitable for a newbie????

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

    Don't.

    tbh tho A and B solvable.

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

      Need to learn a lot. Couldn't solve even 1 ques. :(

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

        If you want easier problems to try on, i personally think the first few problems on AtCoder Beginner Contests are quite suitable. Have fun!

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

    Yes, AB should be easy enough. Go do it!

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

10 minutes delay, sorry. I'm trying to fix Ruby installation.

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    4 years ago, # ^ |
      Vote: I like it +31 Vote: I do not like it

    No problem sir. Codeforces is such a good platform that these types of delays doesn't hurt if contest go on smoothly

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

    Contest smoothness >>>>> 10-15 minutes delay

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

My adrenalin just got wasted

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

Delayed by 10 minutes :/

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4 years ago, # |
  Vote: I like it -264 Vote: I do not like it

What the fuck? Why is CF so bad in punctuality? -_-

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    4 years ago, # ^ |
      Vote: I like it +31 Vote: I do not like it

    you should write the words carefully.They are doing hardwork for us

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

      Agreed but they can't just play with our time? Can they? :)

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

        They don't force you to play this.. are they ?

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

          Did someone force you to comment here? XD

          No hard feelings brother!

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

            Did someone force you to reply here?

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

              Did someone force you to make an entry? :3

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

        Try to compete in virtual contest then.

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

        Did codeforces questioned you ever ? or did they ever ask you to pay for such an amazing platform? Be patient.

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

          Tell me the day you need to pay to codechef or topcoder or any other site that exists!

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

            True, but be patient at the same time.

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

              Yeah bro absolutely! All the best to you for the round! Have a large delta!

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

            Someone is talking about codechef , LOL. Can you please deactivate your codeforces account? And enjoy codechef. All the best :)

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

              Can we deactivate it ? :/

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

            Do we need to state the difference in the quality of Codeforces and Codechef?

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

    A delay of 10 minutes is much better than an unrated contest or queueforces!

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

    Calm Down,man. We all are human, we all make mistakes.

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

    Don't thank MikeMirzayanov if you can't, But please don't hurt the sentiments of the fellow codeforces users.

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

Oh shit! Now I'll have to listen to Twice once again.

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

    Oh shit! You had to listen Twice twice, it's two squared)

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

This ten minute extension is ruining the moment :(

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

my precious time....22:35->22:45

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

Delayed??

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

Is today's contest suitable for newbie and lower pupil?

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

    Yes...I think by solve a,b we can increase our rating easily !!

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

    A and B should be solvable by everyone, I think. But even if they weren't, participating in a contest is always suitable.

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

    Even if you couldn't solve any problem during the contest, you will learn something from the editorial afterward.

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4 years ago, # |
  Vote: I like it -49 Vote: I do not like it

What the fuck! Another 10 minute wasted. 10 min wasted before starting by waiting.

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

    Codeforces is doing hardwork for free. You should not say these 10min wasted. Its way much better than an unrated contest due to long queues.

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

Ok, all set, 5.4.3.2.1 let's start..........not now, come again after 10 min xd

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4 years ago, # |
← Rev. 2   Vote: I like it -16 Vote: I do not like it

[deleted]

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

An interesting observation: all the people complaining about adrenaline being washed out etc. are below blue and below.

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    4 years ago, # ^ |
      Vote: I like it +31 Vote: I do not like it

    Interesting observation: all the people always having problem about something and not taking a joke as a joke are purple and above

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

Codeforces Global Round Exists:

meme.jpg

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

As a contestant, I just read the questions

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

This was the Hardest A i have seen till now.

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

    Not at all :| Hard but not hardest !!

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

      How can you tell me on my behalf.i said i have seen till now,read the comment again.

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

        Cause you attend 62 more contest..it is not so hard.

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

          I think i got horrified from the contest announcement.XD

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

    For me A was harder than B and C. Took me a while to reach the solution

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

      Same here solved A in total 1:30 hrs and C in 10 minutes. xD

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

        But C's logic was beautiful though, i was scared that am i missing some case here.

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

As a tester, I am very happy that I can enjoy others suffering in the contest. This line become true lol. But really awesome problemset

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

i should have taken those feedbacks seriously :(

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

Very good contest nice problemset

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

hope mifafaovo gets dethroned by umnik this time!

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

[*] rating

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

As a participant, this round gave me PTSD. XD

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

    I gave this contest in the hope for specialist but it seems that still specialist is far away from me...

    BTW logic for 3rd one is

    "NO" if(a[0] > a[n-1] ) , else "YES"

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

    I think I need more IQ to solve problem like these, not algorithm knowledge. :)

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

Arggg. Tough round. Great problems, though!

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4 years ago, # |
  Vote: I like it +161 Vote: I do not like it

Ari: how many constructive problems do we need?

Other setters: Yes

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

Great round with difficult problems. Hoping for a fast editorial.

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4 years ago, # |
  Vote: I like it +241 Vote: I do not like it

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

I wonder who did created problem D.

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4 years ago, # |
← Rev. 2   Vote: I like it +185 Vote: I do not like it


Never again.

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

    Thus, hocky went and made a catfish farm instead. He is now known as the catfish farmer.

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

Is there anyone else who could solve D in like 10-15 minutes and has no idea about solving C? Bad day!

Anyways how to solve C?

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

    The last element must be greater than the first

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

    how to solved D ?

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

    arr[0] < arr[n-1] => YES else NO

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

    if(a[n-1]>a[0]) cout<<"YES\n"; else cout<<"NO\n";

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

    if $$$a[0] < a[n - 1]$$$ then "YES" else "NO"

    Consider this example

    5 6 7 4 8 9 10 13 11 12

    This can be visiualize as

    $$$[increasing] [increasing] [increasing]$$$

    5 6 7 4 8 9 10 13 11 12

    But How we are breaking this sequence ?

    We are considering $$$first$$$ and $$$last$$$ will remain in the end of the process. So our focus is to remove all the element in between.

    See,

    4 $$$<$$$ 5 $$$(first element)$$$, this will insert break in our sequence, from this index we will start making new increasing sequence.

    Similarly observe, 13 < 12 $$$(last element)$$$, this will insert a breaking point.

    Now, if you think a little about it, you will see we can merging first increasing sequence and last increasing sequence like this

    5 6 7 4 8 9 10 13 11 12 ==> 5 6 7 4 11 12 ==> 5 6 7 11 12

    So the sufficient condition would be $$$a[0] < a[n - 1]$$$ for answer to be exists.

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    4 years ago, # ^ |
    ← Rev. 3   Vote: I like it +5 Vote: I do not like it

    34 people (and 2 in under the next such question) have replied to this comment but no one has even slightly explained why this is true. What's the use of such responses?

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

      Many of them don't know. :p

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

      I proved it first before solving it. PLease Correct me If I go wrong any where. Let me explain the proof very clearly. if the minimum element of permutation that is '1' is last element of the array then plainly answer is No because no matter which ever operation you performed.the last 2 elements after operation will have minimum element that is '1' on RHS which means it is not possible to satisfy the condition that is a[i]<a[i+1].

      Now if 1 is in a[0] that is in first place then the answer is always "YES" , just converse of I said above.

      Now when '1' is in middle , things become nontrivial. For example 1 is in middle and after applying some sort of operation we reached a state where we have 3 elements and '1' lies in the middle of these elements , then lets say these elements are a 1 b.

      then if a<b then we can delete 1 from the middle and at the end we will have two elements a b since a < b then we can achieve a single element but when a > b we cannot.

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

    Observation 1: you can't make any operation that decreases the 1st element Observation 2: you can't make any operation that increases the last element If the 1st element is greater than the last elements, then in the best case you'll end up with 2 elements [a1 a2] where a1 > a2. Otherwise there is an easy method to eliminate all but 1 element.

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

    You have to remove the greater element in permutation while you can. If this element become the last in sequence, print YES, if you cannot remove the greater element, print NO. This is the key idea

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

Can someone tell how to solve problem C?

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

    If v[1] > v[n] print "NO"

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

    Check if the first element is smaller than the last element

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4 years ago, # |
← Rev. 3   Vote: I like it +107 Vote: I do not like it

Problem setters and testers to all the participants rn:

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4 years ago, # |
← Rev. 4   Vote: I like it +21 Vote: I do not like it

G is a good problem for Div2D?

I guess a subsegment of the problems is reversed before the contest...

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

You will be given 2 hours and 30 minutes to solve 9 problems, and we highly encourage you to read all of them :)

Did they want us to suffer? There is no gap only between A and B, E and F

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

I really need to start thinking in multiple directions before coding. Had I done that I could have solved A much much earlier :(

Leason learnt.

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

Probably should've listened to the Round Feedback.

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

I am pretty much impressed that a trivial thing can be stated in such a difficult way (problem E).

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

    I haven't done anything trivial in E.

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

    Imo the thing not THAT trivial either

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

      I'm not saying solving this problem is trivial, of course. I can accept the opinion that the bubble sort might be non-trivial.

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4 years ago, # |
  Vote: I like it +91 Vote: I do not like it

Why did you put the easiest problem as G?

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

E killed my will to live, how to solve that?

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

    Transform the array into a permutation by considering pairs ($$$a_i,i$$$). Use bubble sort on the inverse of that permutation; each swap of elements which differ by 1 only remove that inversion.

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    4 years ago, # ^ |
      Vote: I like it +35 Vote: I do not like it

    In a non-sorted permutation there is always a pair of consecutive numbers which are in wrong order. You can swap them and it doesn't affect any other inversion.

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

      I tried to implement this for like an hour or more :/ Need to study the solutions.

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

        Hi, I'm still a little confused with the statement that "it doesn't affect any other inversion".

        In eg: 3 1 2, when we swap (3,2) we get 2 1 3, but here we created a new inversion (2,1).

        Can someone explain this please? Thanks.

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

          With 3 1 2 there are two inversions. Positions (1,2) and (1,3). We swap (1,3) because of the min diff of those two inversions. Then we swap the other inversion (position 1 and 2) resulting in 1 2 3.

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

            Why can't we perform swap of positions (1,2) and then (2,3). The value array will transform as follows : 3 1 2 -> 1 3 2 -> 1 2 3

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

              No. 3 1 2 swap positions (1,2) -> 1 3 2 swap positions (1,3) -> 2 3 1

              Note that we do not swap "the positions of..." or something like this. We swap the positions as given in the inversions.

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

                Thanks a lot, the last line cleared all my doubts.

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

What was the approach for A? Felt like I was over-complicating it

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

    print in alternating signs, that was enough

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

      Any proof as to why that always works?

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

        bcs negative minus positive is negative, and positive minus negative is positive

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

        Because in that way every adjacent difference have opposite sign too. That's sufficient.

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

        because positive number — (negative number) will always be positive and negative number — (positive number) will always be negative. this will give equal number of (Ai+1 — Ai) positive and negative numbers.

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it 0 Vote: I do not like it 
    + - + - + continue until n;
or - + - + continue until n;
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4 years ago, # |
← Rev. 2   Vote: I like it 0 Vote: I do not like it

if(CF Rounds==Ad-hoc Problems)

cout<<"100% true";

else

cout<<"0% true";

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

Can anybody tell how to do D problem ?

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

    try to make every element equal to its index ( 0 based )

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4 years ago, # |
← Rev. 5   Vote: I like it -15 Vote: I do not like it

Solution for A B C D:

A:

for _ in range(int(input())):
    am = int(input())
    arr = list(map(int,input().split()))
    for i in range(am):
        arr[i] = abs(arr[i])
    for i in range(am-1):
        if (i&1):
            if arr[i] < arr[i+1]:
                arr[i+1] *= -1
        else:
            if arr[i] > arr[i + 1]:
                arr[i] *= -1
    print(*arr)

B:

Check if there is no cells greater than 4

Check if there is no cells next to border greater than 3

Check if there is no corner cells greater than 2

If all option is true, we can do it Like this

2 3 3 2
3 4 4 3
2 3 3 2

C:

If arr[0] < arr[last] answer is «YES»
Otherwise is «NO»

D:

Repeat till array is sorted{
	Find the MEX
	if MEX == n:
		check if array is already sorted
		if no:
			find the first arr[j] != j:
			    arr[j] = MEX
	else:
		place MEX at arr[MEX] 
}
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4 years ago, # |
  Vote: I like it 0 Vote: I do not like it

Since when was it that, during the System Test phase, only the submissions in queue are marked ? in the Standings page, and those which are not remains showing blue score?

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4 years ago, # |
  Vote: I like it +190 Vote: I do not like it

15 minutes into the contest: Will make it 2200+ today.
After about an hour and a half: depressed

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

Meanwhile testers after warning us ;)

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

Really nice problems tbh xD Sadly I only solved AB

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4 years ago, # |
← Rev. 2   Vote: I like it +117 Vote: I do not like it

Best 8 minutes at the end of the contest ever:

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4 years ago, # |
  Vote: I like it +77 Vote: I do not like it

testers were right

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

Can someone share their approach for D? I tried to convert the given array to {0,1,2,3... n-1} in a step-by-step manner, but It was taking more than 2*n operations.

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

    Same with you.

    I always WA on 1. When I implement it right, then it overflows 2n in the last 4 minutes, which I have not got enough time to solve it before the contest is over.

    I think it will have a smarter way to solve it, because the brute step-by-step is very easy to be found out .

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

    I did the same thing, if MEX < n , a[MEX] = MEX , else I made the largest element such that a[i] != i , equal to MEX. I used a set to keep track of largest element and its index

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

ConstructiveForces

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

How to solve F??

I kept on playing as 2nd player and kept on losing on 1000th turn of testcase 1 (or I have not understood the interaction correctly)

My logic was, for every turn (except for the last one) we will check that we do not make the following two situations after adding y to a (assuming the last move was not on a)-
1. a=b or a=c
2. a is the max of the three piles and a-max(b,c)!=max(b,c)-min(b,c)

If these 2 conditions are satisfied, we can add y to a, else we can check for the remaining pile in the same manner. To start off we can start with any pile which satisfies these 2 conditions.

For the last turn, I will only check condition 1.

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

    the first player always can win

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

    Can you explain your solution D

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

      Yeah, I first removed all the duplicates by always operating on a value which has appeared before in the array. After this our array will be a permutation of [0...n-1].

      Now I just need to sort it. Assume all the array elements as nodes of a graph and there is an edge between i and arr[i].

      this graph will be having multiple cycles. For every cycle with more than 1 node in it, we can operate on any node in this cycle, suppose value of this node is val, after operating it will become n (since our array was a permutation of [0...n-1]). Now important thing is next time when we will operate the value of the node on which we will operate will become val. So why not operate on the node at valth position (since after sorting arr[i] will be equal to i). So we will do that and change val to value of operated node. This will end as the graph is made of cycles.

      After doing this for all the cycles, we will have the sorted array.

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

G (tree modifications)

Let's color vertices with red and black so that any edge always connects a red and a black vertex. Then it's easy to note that each operation either reduces a black vertex or a red vertex (makes it the opposite color).

I counted Nred and Nblack and print the answer as min(Nred, Nblack) — 1.

WA6

Where am I wrong in my assumptions?

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

    Where are you wrong? In your code I guess

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

      Could you see please? Checking my code was all I was doing the last 10 minutes, no luck 85992861

      -- I guess nn is the issue.

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

    I think you didnt initialize your array "nn"

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

      Huh, I can't express the mixture of emotions I have now... Using C++ for contests only has its dark side. And I'm a Java guy, yes...

      Thanks, bro)

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

        I don't now how it is in Java, but PLEASE do not declare arrays locally. Either use vectors or global arrays.

        P.S. Tip: "min" function exists

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

D was a great problem in my opinion.

Approach

Submission

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

    thanks

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

    I had the same idea, and would've solved it if given 5 more minutes. I wasted so much time proving C although I guess most of people just wrote the one liner with a strong intuition. My own fault :(

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

    Easier procedure:

    Step 1: Write $$$mex$$$ to $$$a[mex]$$$ until $$$mex == n$$$.

    Step 2: Find position $$$i$$$ such that $$$a[i] != i$$$. Write $$$n$$$ to $$$a[i]$$$.

    :D

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

      I also tried this approach sir..May be my fault

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

      I solved the same way, but due to poor implementation I got 5 wrong answers

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

    Damn, man. I did step 1, couldn't figure out to do step 2 in less than 2*n operations. Thanks a lot for the approach.

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4 years ago, # |
  Vote: I like it -6 Vote: I do not like it 
Give me some hints to solve D please !!
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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it +3 Vote: I do not like it

    Try to make $$$array[i] = i.$$$

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

    change the array to 0 1 2 ... n — 1 for hint : if mex = x and x < n you can choose a(x — 1) if you dont choose a(x — 1) again mex will never equal to x

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4 years ago, # |
  Vote: I like it +401 Vote: I do not like it

Why did you host atcoder contest on codeforces?

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

I don't know how many people have encountered this problem, but I spent more than an hour on it and still didn't fix it :(

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

Nobody said to me July 5th is April 1st requiem

it was fun

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4 years ago, # |
← Rev. 3   Vote: I like it -8 Vote: I do not like it
The most Ad-hoc problems A, B, C
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4 years ago, # |
  Vote: I like it +206 Vote: I do not like it

OK, you've warned us, I'm quiet.

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    4 years ago, # ^ |
      Vote: I like it +60 Vote: I do not like it

    I'd press F to pay respects, but given the circumstances ...

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4 years ago, # |
← Rev. 2   Vote: I like it +87 Vote: I do not like it

E was well known to me xD https://artofproblemsolving.com/community/c6h380159p2102937 Kinda obscure source (Baltic Way 2007), but I remembered this as an exceptionally nice problem.

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

I spent one and a half hour to make a huge implementation on c and found the elegant solution just after i solved it smh

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

Cried after seeing the solution of C? Can someone give a proof for this?

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

    Try with copy pen and observe .

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

      You may have solved with observation, but there is a good proof. Here it is-

      After each move the first element is increasing and the last element is decreasing; if in some moment there is only one element and a[0] > a[n - 1], the first element should be equal to the last element, but it's not possible (k = last element, then k >= a[0] > a[n - 1] >= k, absurd) If instead a[0] < a[n - 1], there is always a move because the array is never completely decreasing

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    4 years ago, # ^ |
      Vote: I like it +8 Vote: I do not like it 
    1. you can only replace the last element with a smaller one
2. you can only replace the first element with a larger one

- based on these observation we can conclusion that in case first > last we can do nothing so the answer is "NO".

- in case first < last we can easily find a way to remove numbers from 1 to first-1 and that will make the first element is the smallest in the array .... and obviously when the smallest element is in the first we can reduce the size of the array to 1.
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4 years ago, # |
  Vote: I like it +1 Vote: I do not like it

What If I resubmit an Accepted code with one line change ?? My solution has been skipped for system testing?

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4 years ago, # |
  Vote: I like it +153 Vote: I do not like it

1252862

Problem C is one of the sign we humans have reached our advanced civilization.

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

I stucked in B and after the contest when I saw the solution of C of top performers I feel bad for me

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

Fast system testing!

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

Fastest system test.

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

Well, my C story: unsucessfully solving C for 30 min while checking out other problems and trying literally every possible idea on C, checking that C has a ton of solves and I should do something with C, coding and submitting unproven greedy which passed, and after contest finding out that it is just a convoluted way to determine in $$$\mathcal{O}(n)$$$ whether $$$a[0] < a[n - 1]$$$.

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

    As a tester, I was struggling with C for too long, and I did something similar to you.

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4 years ago, # |
  Vote: I like it +51 Vote: I do not like it

In B i got 5 WA because of

Spoiler
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4 years ago, # |
  Vote: I like it -40 Vote: I do not like it

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4 years ago, # |
← Rev. 2   Vote: I like it -92 Vote: I do not like it

.

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

    Wasted 45 mins in C finally got a[0] <= a[n-1] after solving many test-cases.

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

    Already told you, your shitty memes will work only on codechef, not here XD

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

Very good conclusion？

Actually，I was deeply surprised when I saw this F and G.

And even I didn't solve the C by the $$$a_1<a_n$$$.

Rather than blame the survey scope of the person who made the question, it's best to regard it as a opportunity to progress.

lol

upd: the data of F is too weak... You can past it even you forgot to judge the "self-kill"...

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

    Interactor was coded to only ever print 0 if it really can't make a valid move, not sure if that's what you mean.

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

the most frustrating thing is I spent nearly half of the whole competition time on F but didn't get the idea until the last 3 minutes and I didn't complete the code... Anyway, nice contest! thanks the authors and organizers. my rating should increase anyway:p

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

i didnt perform well but contest was amazing.

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

I love the problems in this contest!

Writers and testers thakns!!!

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

nearly 21000 participants registered and only about 8000 solved problem A so either participants are becoming too much conscious about their rating that they don't submit if they didn't solve problem A fast or problems were that tough but i don't think A and B were tough.so its actually the former point

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

    Or they just register in advance without knowing whether they will be able to participate

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

85960902 and 85958960 are exactly same solution including macros and comments

85938310 and 85961324 are exactly same solution including macros and comments

Their handle are also same.

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

    Looking on submissions times I can conclude that he tries to avoid rating decrease on main account in such a way. Looks like new cheating technique on CF discovered (actually, modification of "late submission" strategy for multiple accounts).

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

Today's contest came as a rating dropper for me. A didn't click try solving it for 30 min. Did B fast. Didn't notice that a1<an part. Tried solving it in a different way. Got the idea of D completed the code but because of one break statement kept getting wa. Contest got over than saw my mistake. Great contest Bad Day

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

Hey , I received a message that my code matched with someone. I even dont know this guy. Please recheck our codes and give my rating back for this contest .

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4 years ago, # |
  Vote: I like it +111 Vote: I do not like it

When will the ratings change?

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

Codeforces comment section is addicting.

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

I thought this was code forces, not constructive forces...

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

As soon as I submit a solution, the problem gets locked. I am facing this problem for the past 2 contests. Is there something that can be disabled to solve this issue or it's a bug?

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

    It looks like you locked all the problems around 1:24:00-1:24:30 at slightly different times.

    Was this a scam to make more people add you as a friend? :D

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

      No I have not done it for adding friends. The problem is genuine. The problem got locked after every submission. Once the contest finished, they all got the same time, I dont know how. And even when the problem was locked I was not able to look at the other submissions.

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

      Congrats on becoming Red :D

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

        Wrong, the color of his handle becomes the color of his shirt.

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

    Stop giving your codes to devanshi345 and that might solve the issue. Proof: Devanshi's submission Aman's submission For those wondering how devanshi and aman are relevant, they are siblings. Why would someone make a submission in div3 D and then leave? If you see devanshi's code then you'll see she has added 1 to some variable and then subtracted 2 in the very next line and she has done this twice, you obviously know why. Also I didn't jump to the conclusions directly by looking at one code but I have been observing them closely and have a lot of other codes as proof. Just see devanshi's and aman's submission times for the past few contests, quite strange right? Exposing them won't benefit me and I'm wasting my time and know that well so if anyone has any advice in this context then please stfu and do your job. I felt good after writing this comment and don't care if I wasted my precious 5 mins.

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4 years ago, # |
  Vote: I like it +72 Vote: I do not like it

Codeforces predictor showed that I was going to get 66 rating, but I only got 64. I feel scamed :(

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

    Oh, I see these 2 points in your case meant a lot :D Congrats on approaching to red zone!

    Rating prediction is inaccurate because CF doesn't provide "true" rating for new accounts. If I subtract 2-3 points from a rating prediction for every person, would this make contestants happier?

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4 years ago, # |
← Rev. 2   Vote: I like it -41 Vote: I do not like it

OMG

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

    Other account? Main account? What are you even talking about?! You can’t have more accounts! You are just a cheater.

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

    do you even read agreement before signing up for the contest?

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

    It's not sensible because you consciously registered in both 2 accounts which means you willing to cheat. I am right? :))

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

seems that increasing ratings are getting less and less if you do the same amount of problems in each contest.

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

    To see the first 5 contest you can not judge.cause after 5 contest your rating Will br balanced.its the new rule

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

Could anyone tell me the solution of the A :((

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

The Integer Game question was one of the best and greediest interactive questions I have seen on CodeForces.

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

As a contestant i increased my rating!! Thank you for this great round!!

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

What a good contest! This contest is involving many knowledge points, like constructive, constructive and constructive, or guess one conclusion, second conclusion, and third conclusion. That's fantasitic, isn't it?

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

    Yes, it was a great contest. The implementation of problem D was really good. It would be better if problem-setters include more of the problems on data structures in C and D problem.

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4 years ago, # |
← Rev. 2   Vote: I like it -53 Vote: I do not like it

The contest would've been better if not all questions were of similar category.

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4 years ago, # |
  Vote: I like it +132 Vote: I do not like it

Congratulations to the t-shirt winners!

List place Contest Rank Name
1 1375 1 tourist
2 1375 2 scott_wu
3 1375 3 yosupo
4 1375 4 Um_nik
5 1375 5 Rewinding
6 1375 6 lqs2015
7 1375 7 heno239
8 1375 8 Motarack
9 1375 9 zeronumber
10 1375 10 Itst_boyfriend
11 1375 11 LayCurse
12 1375 12 Golovanov399
13 1375 13 mrscherry
14 1375 14 EnEm
15 1375 15 conqueror_of_tourist
16 1375 16 Swistakk
17 1375 17 hos.lyric
18 1375 18 ohweonfire
19 1375 19 ksun48
20 1375 20 gop2024
21 1375 21 TLEwpdus
22 1375 22 HashimotoNanami
23 1375 23 Sulfox
24 1375 24 stevenkplus
25 1375 25 neal
26 1375 26 Amoo_Safar
27 1375 27 sunset
28 1375 28 SirShokoladina
29 1375 29 kort0n
30 1375 30 zylber
53 1375 53 KayacanV
95 1375 95 PavelKunyavskiy
128 1375 128 aid
145 1375 145 sugarrr
154 1375 154 peti1234
173 1375 173 Pyqe
175 1375 175 SoMuchDrama
210 1375 210 rotavirus
219 1375 219 Rahul
239 1375 239 adurysk
247 1375 246 MonkeyKing
270 1375 270 PogosovArseny
277 1375 277 shenxy13
292 1375 292 hyeon_gyu
360 1375 360 ollpu
433 1375 433 QCFium
439 1375 439 QieziMin
447 1375 447 MinhazIbnMizan
481 1375 481 Kapusha
498 1375 498 SeehtEntity
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4 years ago, # |
  Vote: I like it +31 Vote: I do not like it

instead of calling this contest as global round 9, rename it to constructive algo contest

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

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