Devil's blog

Codeforces Round #659
By Devil, 6 months ago, In English

Hello, Codeforces!

I'm very glad to invite you to the first Cuban round Codeforces Round #659 (Div. 1) and Codeforces Round #659 (Div. 2) which will take place on Jul/24/2020 17:35 (Moscow time).

All problems in this round were created and prepared by marX, gilcu3, dcordb, jcg and me. We tried to make them interesting and diverse and hope that you will enjoy them!

You will be given 2 hours to solve 6 problems in both divisions, and we highly encourage you to read all of them :)

We would like to thank:

The score distribution will be announced shortly before the round (or earlier).

UPD: Here is the score distribution:

Div2: 500 — (500 + 750) — 1750 — 1750 — 2500 — 2500

Div1: 1000 — 1000 — 1750 — 1750 — 2000 — 2250

Good luck and have fun!

UPD: The editorial is ready Editorial

UPD: Congratulations to the winners!

Especially for tourist, Benq and Radewoosh who solved all the problems!!!

Div. 1:

  1. tourist

  2. Benq

  3. Radewoosh

  4. ksun48

  5. jiangly

  6. yosupo

  7. ecnerwala

  8. Egor

  9. Marcin_smu

  10. ainta

Div. 2:

  1. AhoCorasick

  2. okikust

  3. crystal302

  4. ServantSaber

  5. Kirill_Kudr22

  6. fakeQingyuShi

  7. tripPple_A

  8. CodeSlayer4425

  9. ZADaCHI

  10. ITO

 
 
 
 
  • Vote: I like it
  • +732
  • Vote: I do not like it

Comments Comments (628)
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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I hope for an interesting first cuban round :)

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    6 months ago, # ^ |
      Vote: I like it +43 Vote: I do not like it

    This round was not at all interesting.

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    6 months ago, # ^ |
    ← Rev. 2   Vote: I like it +150 Vote: I do not like it

    It looks like someone forgot to mention that the contest was for Russian 5th to 8th graders. (No offence intended).

    Anyways, this just makes it more exciting. Thanks for this round.

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    6 months ago, # ^ |
      Vote: I like it +86 Vote: I do not like it

    New round to avoid : Cuban Round

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    It became really interesting when I tried submitting the first problem and not to mention, when I started reading Problem B.

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    6 months ago, # ^ |
    ← Rev. 2   Vote: I like it +98 Vote: I do not like it

    Who is this Koa the Koala and why does she want to cross the shore?

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      6 months ago, # ^ |
        Vote: I like it +76 Vote: I do not like it

      Google's first result for "can koala swim?"

      "Koalas drown in swimming pools when they are looking for water to drink. Although koalas can swim, if there are no assisted ways for a koala to climb out they will eventually drown."

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    6 months ago, # ^ |
      Vote: I like it +41 Vote: I do not like it

    did someone forget this was a coding round and not a reading round?

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    why is everyone downvoting because of the contest... :(

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    6 months ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    I started reading the first problem , and before i could even see the test cases , the round was over...

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

      I suggest improving your reading comprehension before trying a competition. Good Luck!

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    I would rather do Eva than doing these problems

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

    Score for B1 should be more than C. Currently B1 score is significantly low than that of C. And every one knows the level of these 2 questions.

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      The contest is in general more difficult than other Div. 2 contests; but yes, we definitely should look into the reason that problem B1 and C had such a contrast between difficulty and score.

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    6 months ago, # ^ |
      Vote: I like it +21 Vote: I do not like it

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    After seeing too many Red coders as testers, we should prepare ourself for such a lengthy, disordered(e.g. problem B and C order) round.

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6 months ago, # |
  Vote: I like it -82 Vote: I do not like it

Shitty memes incoming!!!!!!

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6 months ago, # |
  Vote: I like it -34 Vote: I do not like it

.....

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6 months ago, # |
  Vote: I like it -44 Vote: I do not like it

Lol you are from Havana University

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6 months ago, # |
  Vote: I like it -16 Vote: I do not like it

what is cuban round ?

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6 months ago, # |
  Vote: I like it +302 Vote: I do not like it

As a tester, I finally get to make one of these posts.

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6 months ago, # |
← Rev. 4   Vote: I like it -55 Vote: I do not like it

This comment was downvoted by trolls

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    6 months ago, # ^ |
      Vote: I like it +78 Vote: I do not like it

    Come with me sir, we're gonna find out who tf asked.

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6 months ago, # |
  Vote: I like it +73 Vote: I do not like it

Last time with this much red coders, we saw something dangerous.

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

When last contest is rated and you want another contest to participate in and you are happy and confused at the same time!!!:

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6 months ago, # |
  Vote: I like it +56 Vote: I do not like it

Will it be IQ test round? I like IQ tests.

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    6 months ago, # ^ |
      Vote: I like it +424 Vote: I do not like it

    As a tester, I can confirm you need a brain to solve these problems.

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      6 months ago, # ^ |
        Vote: I like it +56 Vote: I do not like it

      Writing 'As a tester' was really important for that confirmation :p

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      6 months ago, # ^ |
      ← Rev. 2   Vote: I like it +56 Vote: I do not like it

      hu_tao How much problems did he reject this time xD :)

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        6 months ago, # ^ |
          Vote: I like it +112 Vote: I do not like it

        I'm pretty sure he rejected ~15 problems

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          6 months ago, # ^ |
            Vote: I like it +19 Vote: I do not like it

          After the contest can we have the rejected problems for practice?

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      6 months ago, # ^ |
        Vote: I like it +29 Vote: I do not like it

      After the contest, I was convinced that I have no brain :(

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      6 months ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      Man...I should have read this before the contest:(

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

      As a human being, I can confirm that everyone has a brain smh.

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    6 months ago, # ^ |
      Vote: I like it -25 Vote: I do not like it

    no

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6 months ago, # |
  Vote: I like it +103 Vote: I do not like it

As a tester, I’m glad I tested.

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    6 months ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    Seems like we are again going to have round 657 with less than few hundreds people solving C

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    6 months ago, # ^ |
      Vote: I like it -8 Vote: I do not like it

    [Enjoy your contribution] .

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    As a participant, I should've known what you were saying.

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    6 months ago, # ^ |
      Vote: I like it +62 Vote: I do not like it

    Now we know what happens when DEVIL himself wishes Good luck

    Capture)

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6 months ago, # |
  Vote: I like it +30 Vote: I do not like it

There is an amazing team behind this contest. I'm looking forward to participate. Good rating everyone

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6 months ago, # |
  Vote: I like it +74 Vote: I do not like it

As a non-tester, I'm glad that I'll be able to participate in it <(")

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    6 months ago, # ^ |
    ← Rev. 2   Vote: I like it -27 Vote: I do not like it

    There was an attempt. Note-The comment I replied to had downvotes when I wrote the comment

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    So, how did the contest go for you ? XD

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      My ratings didn't go down, so it was good I guess :\

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

So happy

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    Still holding to this opinion after the contest? ¯_(ツ)_/¯

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      It's irony, the contest is so happy, it's like yesterday's contest.

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6 months ago, # |
  Vote: I like it +11 Vote: I do not like it

Imagine getting back from retirement for a Cuban round, writers are all amazing. Looking forward to it, see you in the standings, altho I prolly don't pass a,b :). Удачи

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6 months ago, # |
← Rev. 2   Vote: I like it +13 Vote: I do not like it

The Div1 part of the contest is shown in Calendar on saturday, too. I think this is not intentionally.

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

We still remember the last red round

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6 months ago, # |
  Vote: I like it +9 Vote: I do not like it

After a long time Um_nik became as a tester. I hope this round will be great.

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6 months ago, # |
  Vote: I like it +13 Vote: I do not like it

It's a good opportunity for me to become PUPIL again :)

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6 months ago, # |
  Vote: I like it +37 Vote: I do not like it

Congratulations! :)

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6 months ago, # |
  Vote: I like it +44 Vote: I do not like it

Yes, i have heard of Cuban. Krasnodar is the best city.

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    6 months ago, # ^ |
      Vote: I like it +55 Vote: I do not like it

    No no no, not that Cuban. This Cuba

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      6 months ago, # ^ |
        Vote: I like it +29 Vote: I do not like it

      Why do you downvoting me? That was just a joke. Of course i know what cuban means. Why do you upvoting some captain obviousness who didn't get the joke and tried to "explain" me what Cuban is?

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        6 months ago, # ^ |
          Vote: I like it +16 Vote: I do not like it

        Some people just don't get sarcasm, man. I upvoted you and am glad that your comment is now receiving upvotes too.

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    6 months ago, # ^ |
    ← Rev. 2   Vote: I like it -26 Vote: I do not like it

    .

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6 months ago, # |
  Vote: I like it +53 Vote: I do not like it
Div2 A
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6 months ago, # |
  Vote: I like it -23 Vote: I do not like it

As a participant, I am all scared looking at so many Reds

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

You can do it! who want to become green, blue, ...

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6 months ago, # |
← Rev. 3   Vote: I like it -24 Vote: I do not like it

Alright.

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6 months ago, # |
← Rev. 2   Vote: I like it -69 Vote: I do not like it

Ok

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    6 months ago, # ^ |
      Vote: I like it +14 Vote: I do not like it

    shut up!!

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      6 months ago, # ^ |
        Vote: I like it -18 Vote: I do not like it

      Your DP says that you stopped caring a long time ago then why is it bothering you. Everything gonna be alright!

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

Very excited for my first contest! I have covered all the basic data structures in past 1 month . Now I am looking to take part more frequently . Any suggestions on how to be consistent and any further resources ??

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

    Bad Luck ! You chose the wrong contest.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    https://www.youtube.com/watch?v=dQw4w9WgXcQ This link is to an excellent youtube video. He covers a lot of things that I believe every competitive programmer should learn, be sure to check it out!

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      paid attention to how many dislikes there were?

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

        The video is great bro, you're an absolute idiot if you think its bad.

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          6 months ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          I don't think he's bad. Regarding your categoricalness, I think the following: that you are over 40 years old, or you are from Cuba

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6 months ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

In codeforces round When I submit the problem and it gets pretests passed in very first submission. Ooh that feelings can't explain in words. When I am writing this I am crying with smiling face

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

    I think you haven't experience that feeling when you submitted it WA 10 times and the 11th time is got Pretest passed. Literally crying with smiling face.

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6 months ago, # |
  Vote: I like it +26 Vote: I do not like it

As a tester, I wish every participant good luck and high rating on this (very nice) round!

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

I Hope Cuban round will be as good as Cuban Cigar. :)

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6 months ago, # |
  Vote: I like it +47 Vote: I do not like it

A very interesting score distribution!

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    6 months ago, # ^ |
      Vote: I like it +16 Vote: I do not like it

    score and difficulty level no match at all !

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6 months ago, # |
← Rev. 2   Vote: I like it +116 Vote: I do not like it

Perfectly balanced, as all things should be

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6 months ago, # |
← Rev. 2   Vote: I like it +60 Vote: I do not like it

( ° ͜ʖ °)

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    6 months ago, # ^ |
      Vote: I like it +168 Vote: I do not like it

    He should have waited for CF round #666.

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      6 months ago, # ^ |
        Vote: I like it +57 Vote: I do not like it

      How about we reserve CF Round #666 to be held on 13th November, 2020 (Friday the 13th) and ask Devil to hold it?

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        6 months ago, # ^ |
          Vote: I like it +28 Vote: I do not like it

        Only 7 contest in 4 month? I will lose my sanity

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

          Maybe we can try "some" educational rounds!

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      5 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Round 666 is coming up :)

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    6 months ago, # ^ |
      Vote: I like it +22 Vote: I do not like it

    lets make it 666 again

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    6 months ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    The cursed contest.

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6 months ago, # |
  Vote: I like it +9 Vote: I do not like it

Wait, do we have subtasks in div2(asking because of the score distribution/and that it isn't mentioned)

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I suppose because in the format given like (750 + 750 ) suggests so

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    It is written there will be 6 problems, so I think (500+750) => B1 and B2, B1 being subtask:)

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6 months ago, # |
  Vote: I like it +1 Vote: I do not like it

I think that you should also author the seventh round following this one.

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6 months ago, # |
  Vote: I like it +14 Vote: I do not like it

hello darkness, my old friend

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

Will Tourist top the tables today??

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6 months ago, # |
  Vote: I like it +16 Vote: I do not like it

Hope,this first cuban round will be very interesting :D

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

Interesting score distribution! GL & HF!

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6 months ago, # |
← Rev. 5   Vote: I like it -12 Vote: I do not like it

ups

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6 months ago, # |
  Vote: I like it -27 Vote: I do not like it

Insha Allah, would be able to cross 1500 today!!.

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6 months ago, # |
  Vote: I like it +11 Vote: I do not like it

A sub-task for B? This is going to be wild.

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6 months ago, # |
  Vote: I like it -10 Vote: I do not like it

Difficulty 1750, hope I could solve them.

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6 months ago, # |
  Vote: I like it +66 Vote: I do not like it

My schedule this summer,

EAT -> PARTICIPATE IN CF CONTEST -> READ EDITORIAL -> SLEEP

REPEAT

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

good luck to you ！！！

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6 months ago, # |
  Vote: I like it +5 Vote: I do not like it

MikeMirzayanov Just curious to ask when running 2 contests (Div1 and Div2) you use the same server fot both the contests or 2 different servers (with Div1 having less specification server because of load)

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

awaiting a great round

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6 months ago, # |
  Vote: I like it +2 Vote: I do not like it

Another Anton Round!

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

tourist registered for the contest, I think he'll take his position today!

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6 months ago, # |
← Rev. 2   Vote: I like it -7 Vote: I do not like it

i am having 1940 rating. and I don't want it to decrease for next 2 month so just wondering if someone can tell me how much maximum rank can ensure me 0 decrease? like any idea? is around 1000 fine

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    If you tell me, in detail, why you want your rating to stay at 1940 for next 2 month, I will seriously consider helping you. thanks

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    6 months ago, # ^ |
      Vote: I like it +15 Vote: I do not like it

    There is a way:copy code and get "skipped".But your account might be blocked

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I am very glad to accept your invitation. I would also like to thank everyone who contributes to the making of this contest. Good luck and have fun!

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6 months ago, # |
  Vote: I like it +33 Vote: I do not like it

photo-2020-07-24-17-23-42 .

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    6 months ago, # ^ |
      Vote: I like it +64 Vote: I do not like it

    The meme is as hard to understand as solving Div.1F

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

    incase anyone didn't get the meme carefully read the second line of the announcement!

    See Here
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6 months ago, # |
  Vote: I like it +99 Vote: I do not like it

The new strategy to decrease server load is working!

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

Seems Red Coders doesn't think of beginner coders !!

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6 months ago, # |
  Vote: I like it +19 Vote: I do not like it

Again a Div1 type contest :(

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6 months ago, # |
  Vote: I like it -28 Vote: I do not like it

The worst contest I've seen and thanks for 2-hour-long terrible time.

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6 months ago, # |
  Vote: I like it +10 Vote: I do not like it

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6 months ago, # |
  Vote: I like it +32 Vote: I do not like it

Glad I didn't submit even a single code!

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6 months ago, # |
  Vote: I like it +1 Vote: I do not like it

div2 feels like div1 :(

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6 months ago, # |
  Vote: I like it +144 Vote: I do not like it

Last contest was such a class. Back to unnecessary complicated questions. All problem setters should learn something from 1-gon and Ashishgup.

I know I am going to get downvoted to hell, but needed to get the truth out.

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    6 months ago, # ^ |
      Vote: I like it +26 Vote: I do not like it

    +1,I love Monogon's problem and this contest is quite bad.

    Some of Ehab's math problem are also good.

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    6 months ago, # ^ |
      Vote: I like it +5 Vote: I do not like it

    Since ^ comment is getting some attention, I want to add if we can come up with a way to voice our opinion about the round? Maybe upvote/downvote a contest or individual problems?

    I am not against harder problems but there's a difference between good kind of hard and bad kind of hard.

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

UPD: Figured what was wrong on pretest 3. Sorry for spreading hate.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I'm a newbie. I didn't even understand the questions.

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

my confidence is indirectly proportional to length of questions

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    6 months ago, # ^ |
      Vote: I like it +11 Vote: I do not like it

    My confidence is directly proportional to length of questions. I cannot solve and more people cannot solve.

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      not being able to solve take a toll on confidence

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6 months ago, # |
  Vote: I like it +37 Vote: I do not like it

Reading div2 B1-B2 problems is more difficult than doing a plank.

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6 months ago, # |
  Vote: I like it +48 Vote: I do not like it

Worst score distribution i have ever seen in Codeforces!!!

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

Div-2 contest doesnt seem to a div-2 type.No balance in problems at all.

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6 months ago, # |
  Vote: I like it +13 Vote: I do not like it

Looks like Devil's plan at work here.

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6 months ago, # |
  Vote: I like it +18 Vote: I do not like it

If the frequencies of these types of contest increases, it will inculcate the feeling of fear in beginners' mind towards competitive coding. No offense to anyone.

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6 months ago, # |
  Vote: I like it -10 Vote: I do not like it

you asked for harder questions, so there you go :P

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6 months ago, # |
  Vote: I like it +60 Vote: I do not like it

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6 months ago, # |
  Vote: I like it +27 Vote: I do not like it

Me after reading Div2 A, B1, B2:

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

Not worth complaining about the difficulty of the problems. Just improve next time and learn from your mistakes.

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6 months ago, # |
  Vote: I like it +19 Vote: I do not like it

Do not trust someone whose account name is Devil

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6 months ago, # |
  Vote: I like it +30 Vote: I do not like it

Kudos to all problem setters and team. What a contest. I realized that need to learn more practice more.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

i was able to solve the first one phewwww!

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    That's an achievement. Not kidding at all. You should be proud of yourself. I am unable to figure out where my code is failing for past one hour.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Yes..me too...really ..pheeewwwwww

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6 months ago, # |
← Rev. 2   Vote: I like it -31 Vote: I do not like it

[Deleted]

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6 months ago, # |
  Vote: I like it +53 Vote: I do not like it

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6 months ago, # |
  Vote: I like it +123 Vote: I do not like it

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6 months ago, # |
  Vote: I like it +135 Vote: I do not like it

Another difficulty staircases

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    6 months ago, # ^ |
      Vote: I like it -37 Vote: I do not like it

    Yeah, and I bet most of users solved problem B by guessing solution, not even having proof...

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      You'd bet that but you'd be wrong. If you actually could guess the solution, then it wasn't too hard to prove three or four cases.

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    6 months ago, # ^ |
      Vote: I like it +10 Vote: I do not like it

    In my opinion

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6 months ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

I thought WA on pretest 2 sucks the most, but today I learnt, WA on pretest 3 sucks the most. Getting WA on pretest 3 in C :(

Nvm I removed an if case and it worked. :)

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6 months ago, # |
  Vote: I like it +27 Vote: I do not like it

tourist returns to #1 !!!

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

Wait... Has Codeforces increased the difficulty of Div.2???

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6 months ago, # |
  Vote: I like it +63 Vote: I do not like it

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6 months ago, # |
  Vote: I like it +120 Vote: I do not like it

<
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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Div2A seems easy (a bit long however), works fine in my testing, but what is in that pretest 2?! Desperate for the editorial!

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6 months ago, # |
  Vote: I like it +26 Vote: I do not like it

The language of Div.2 B1 was very bad. :(

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6 months ago, # |
  Vote: I like it +52 Vote: I do not like it

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

I happy for tourist, he will return to it's normal position :) tourist

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    6 months ago, # ^ |
      Vote: I like it +12 Vote: I do not like it

    You should not add someone's handle unnecessarily

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6 months ago, # |
  Vote: I like it -44 Vote: I do not like it

1-gon's Div.1 contest was MUCH better than today's contest. problems were unbalanced and Div.1 B was terrible problem...

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6 months ago, # |
  Vote: I like it +28 Vote: I do not like it

TFW you not only fail to solve div1A, but can't understand why your solution to div1A is wrong.

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

    Same! But I suppose I'm somewhat relieved/surprised to see a grandmaster say this! No offense ofc.

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    6 months ago, # ^ |
    ← Rev. 2   Vote: I like it +34 Vote: I do not like it 
    aabb
xyxy

    I still have no idea how to solve that problem, although something did pass pretests eventually. Had to move to more trivial problems like E instead :)

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Go through all letters in increasing order. For each letter, get the minimum of letters that this letter needs to be converted to (lets aabb — xyxy: a converts to x and y, take the smaller one), then convert all the letters (a) to the lexicographically smaller one (x or y) (note you need to skip letters that are already ok).

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      What do you mean?

      For that one it's aabb bbbb xbxb xyxy

      (according to my code + my manual attempt)

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      6 months ago, # ^ |
        Vote: I like it +5 Vote: I do not like it

      So the transitive reduction of a DAG isn't a subgraph?

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

        Transitive reduction requires that there is a path from a to b if and only if there was a path from a to b in the original graph. This problem doesn't have the "only if" requirement.

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          6 months ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          24 (Dadgum.)

          I thought that adding more edges can't hurt the number of operations...

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      Acc. to my code, aabb->xxbb->xxxx->xyxy

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Yes! Me too. WA on pretest 3...

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I also had a wrong pretest 3 at first and then I implemented a (in my mind) equal solution in a different and it worked lol (solution is back down). What I did it first was: go through letters in increasing order, if a letter is not good then convert it to a letter that also exists and needs to be converted to the same letter (ignore if it's already good, convert directly only if there are no such cases). Idk why this approach is any different than my other, could be just a program error since it's a bit more complex.

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

    I spent two whole hours battling pretest 3, only to no avail.

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6 months ago, # |
  Vote: I like it +46 Vote: I do not like it

It feels like the contest is based on some olympiad for students of 5-8 grades

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6 months ago, # |
  Vote: I like it +11 Vote: I do not like it

I have a strange question. Who is Koa the Koala?

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6 months ago, # |
  Vote: I like it +27 Vote: I do not like it

Kind request to stop such bullshit Div2

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    6 months ago, # ^ |
      Vote: I like it -12 Vote: I do not like it

    I don't think anyone is listening.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

lol, there was a duplicate test case in problem B. ~~~~~ 5 2 3 1 2 3 2 2 ~~~~~

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

    I was unable to reach sample test case left the problem after reading the problem statement only.

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6 months ago, # |
  Vote: I like it +47 Vote: I do not like it

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

I wish this round to be magically unrated....

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6 months ago, # |
  Vote: I like it +17 Vote: I do not like it

bad problems , bad statements . didn't enjoyed this contest .

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6 months ago, # |
  Vote: I like it -9 Vote: I do not like it

This contest is not worth 2 hours of 20k Div-2 participants.

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6 months ago, # |
  Vote: I like it +30 Vote: I do not like it

thanks antontrygubO_o for amazing coordination of this round.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Anybody else having had problems opening the page of their room?

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

Devil $$$2B$$$, Devil $$$1C$$$.

Devil Statement, Devil difficulty.

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6 months ago, # |
  Vote: I like it +16 Vote: I do not like it

Can someone explain why this idea gives WA3 in Div2-C / Div1-A?

If any letter needs to be changed to an alphabetically smaller one, output -1.

Otherwise, build a directed graph (e.g. a matrix) where graph[a][b] = 1 iff we need to change a to b at least one index, a<b.

Then, drop the unnecessary edges. An edge a->b is unnecessary iff there is another path with more nodes that connects a and b. Note that the path will contain strictly shorter (in the alphabetic sense) edges, so we can start with an empty graph and add edges of alphabetic difference 1, 2, 3, ... 19, at each point checking that the letters are not already connected.

The answer is the number of edges in the final graph. I have no idea what I'm missing.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    i did the same thing, WA on tc 3.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    So on the test AB, DC you will print 3, because A->B->C->D, right?

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

      My answer is 2. The original graph does not contain a->b or c->d, and I only ever remove edges.

      Edit: Okay, I see it. The entire problem is that I only remove edges. For example, in aabb -> cdcd the optimal solution is to turn aabb -> bbbb and then two more operations. My solution prints 4 because it cannot add the edge a->b.

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        6 months ago, # ^ |
          Vote: I like it +12 Vote: I do not like it

        Ah ok, AABB CDCD, the answer is 3, because AABB->CCBB->CCCC->CDCD

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      shouldn't it be 2? coz A -> C and B -> D ?

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

    Got it

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    aabb cdcd

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    I did something weird, but it passed pretests somehow... basically ignore the fact that the graph is directed, answer = 20 — number of connected components.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    this problem can be solved by a simple dfs finding number of vertices in every component.

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

      infxx Can you please elucidate? I tried something similar but it didn't work. 87922305

      The major difference I see is that you are making the graph undirected(right?). Why so?

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Norrius What is the fix for this approach?

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      It's really easy: just find the sizes of (undirected) connected components with DFS/BFS, let's say they are $$$c_1, ..., c_k$$$. Then the answer is $$$\sum_i (c_i - 1)$$$, because there is some spanning tree in each of the components, and you know how many edges a tree has.

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

        I don't quite get the intuition behind this fix? Like, how did you get to this? And why does that work? I get this idea that we need to find the minimum spanning tree(taking all edges' weight as 1) for our original directed graph(but there's an issue in it). But I do not get it that how making the graph undirected solves our issue?

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6 months ago, # |
  Vote: I like it +374 Vote: I do not like it

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

well

That was different

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    each participant's state during contest was exactly like your profile pic ...

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6 months ago, # |
← Rev. 2   Vote: I like it +5 Vote: I do not like it

For Problem D in div 2., can we solve the problem for each bit independently?

Edit: NVM I just proved it to my self

Proof: if you have an odd number of bits, set at a particular position for all numbers in the array, the winner will be decided in this round Other wise you have an even number of bits, and your opponent will get the same result as you for that bit position.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

After giving this contest I feel demotivated a lot.But, also excited like Shoyo Hinata.I have to train harder.Thats the lesson of this contest.Move ON.

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6 months ago, # |
  Vote: I like it +48 Vote: I do not like it

1384B1 - Koa and the Beach (Easy Version) is my new favorit of shittiest problem statement ever.

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

    Pictures would have helped.

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      6 months ago, # ^ |
        Vote: I like it 0 Vote: I do not like it

      And some other story, mayby one which makes some sense or none at all... I needed to ask twice before understanding that the girl cannot swim if the water is to deep. How can somebody come up with such wired picture? This is simply the opposite of logic. I mean, why?

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Yeah, adding "More formally, " just made it harder to understand.

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6 months ago, # |
  Vote: I like it +67 Vote: I do not like it

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

Too time-consuming when reading Div2B problem :))

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6 months ago, # |
  Vote: I like it +91 Vote: I do not like it

So laughy to hear, when problems are nice in easy contest, and bad in hard contets. LOL. bad != hard.

Problems were cute && hard, div2 guys just cant solve them and find it is bad && want unrated — it is so stupid && two-faces

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    The problems were pretty good, it's just the fact that C was a lot easier than B in div2 (You can look by yourself). I find B as a very nice problem, but it took me more than 15 minutes to understand the statement.

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      6 months ago, # ^ |
        Vote: I like it +17 Vote: I do not like it

      Yeah, you are right. I am just angry about people who wrote that problems were bad and shitty

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

        I understood you. I'm also finding this annoying. If you understand the statements of the problems, they are enjoyable (in my opinion). I just hope that in the future, the authors will write the statements more concisely and the problems will go in increasing difficulty.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Finally a really accurated opinion. I left this community two years ago, when i retired from regionals. Now two years without basically coding at all, i return for the first cuban round, and i managed to solve A, B1, C and get a positive score given by the fact that when i retired there were approx 4000-6000 participants per round in Div2. I found out that now there are nearly 20k, but 16k of them at least, only know to cry about problems that a retired person can solve with 0 warn up, thanks so much codeforces, for leaving me this bad memory as about the first round written by my country.

    To the person who i'm replying, really my most sincere congratulation, for not being one of those crying babies. Thanks!

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

Anyone else with wrong answer on pretest 3 in C? What was it??? :/

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    me :(

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    6 months ago, # ^ |
      Vote: I like it +1 Vote: I do not like it

    I guess that was the first real test with many test cases. Test 2 contained some corner cases I think

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Me too. T.T

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Same here. Not sure what it was, but I know I did not handle a case like: aabb cdcd (Answer should be 3: converting a->b, then b->c and b->d)

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

C was DSU or DFS/BFS/ Spanning Tree loved solving it <3;

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    It was easy greedy. You overkilled it. Can you briefly say about dsu solution?

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

      I converted all conversions into the form of A to B in a directed graph if at the end of all conversions character A was required to be converted into B . Now if A>B then always answer is "-1" , this is self explanatory. Now I added all the edges to the graph , if A-->B , Now any successful completion or conversion can can be done efficiently if for every pair A to B to which conversion is required we follow exactly one path and no more than that , this conversion can be seen as path from node A to node B in the graph. Now for a connected components if we want minimum paths to follow and connect all characters which are need to be converted into one path, we need to find just a spanning tree of the obtained graph. Thus we can obtain it easily using any technique like BFS/DFS/DSU . Thus it was a good problem of Spanning tree, I think. May be I over-killed it.

      Consider the small case graph where aab-->bcc A->B , B->C, A->C. since the spanning tree of above graph will be A->B->C , which is minimum possible answer for this conversion process.

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        6 months ago, # ^ |
          Vote: I like it +1 Vote: I do not like it

        Wow, that's an elegant approach. Thank you :)

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          6 months ago, # ^ |
            Vote: I like it 0 Vote: I do not like it

          Yours Welcome , What is the greedy approach by the way.

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            6 months ago, # ^ |
              Vote: I like it +1 Vote: I do not like it

            Created a directed graph.

            Then I traversed from the character 'a'. Assuming our current character is 'C'th.

            Using one operation, I changed all character 'C' to the minimal character over all his sons, and now add the new childs to the minimal character.

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

            AM_I_Learning What is wrong with my solution 87922305?

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        6 months ago, # ^ |
          Vote: I like it +1 Vote: I do not like it

        Very interesting approach, thanks for sharing.

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    6 months ago, # ^ |
      Vote: I like it 0 Vote: I do not like it

    Can you please share your approach

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6 months ago, # |
  Vote: I like it -101 Vote: I do not like it

Time for antontrygubO_o to resign. What a disaster.

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6 months ago, # |
  Vote: I like it 0 Vote: I do not like it

problem b is very complicated to understand. This type of problem shouldn't be in div2

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

In my opinion Div 2 C (Div 1 A) was waaaaaaaay easier than Div 2 B.

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

New type of contest to avoid : Cuban Round

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

    derji v kurse, zachem ty napisal ob etom 100 kommentov lol?

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6 months ago, # |
← Rev. 2