Stepavly's blog

Codeforces Round #650 (Div. 3)
By Stepavly, history, 4 years ago, translation, In English

Hello, Codeforces!

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Hello! Codeforces Round 650 (Div. 3) will start at Jun/16/2020 17:35 (Moscow time). You will be offered 6 problems (one of them will have subtasks) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have a rating 1600 or higher, can register for the round unofficially. The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. We tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as trusted participants of the third division, you must:

  • take part in at least two rated rounds (and solve at least one problem in each of them),
  • do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

The problems for this round were invented by MikeMirzayanov, me and Supermagzzz and prepared by me and Supermagzzz.

Thanks to MikeMirzayanov for platforms and coordination of our work. Thanks to harlequen, manta1130, lynmisakura, Gassa, Rox, antontrygubO_o, armoking, JustasLe, iankury, Sho, bugdone, Khairy for help in round preparation and testing the round.

Good luck!

Editorial

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  • Vote: I like it
  • +384
  • Vote: I do not like it

Comments Comments (352)
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4 years ago, # |
  Vote: I like it +147 Vote: I do not like it

I literally started missing vovuh

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

    Yes we all do :(

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    4 years ago, # ^ |
    ← Rev. 2   Vote: I like it +450 Vote: I do not like it

    Hi everyone who mentioned me in this blog (I wonder that there are so many mentions!). I didn't do any rounds because of my university exams period. But now it is ended and I'm done with it. So I'll return a bit later with another Div.3 round (I need time to come up with problems, discuss and prepare them). Do not worry about me, I am fine :)

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

      and being so busy you found time to reply us all. Thats what increases our love for you.

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

      Then i am excited to see you participate in some div3 rounds.

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      4 years ago, # ^ |
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      we are for div-3 and div-3 for you

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

      More up-vote than the main one.. it's all about vovuh popularity :3 <3

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

    Is it rated.

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      4 years ago, # ^ |
        Vote: I like it +43 Vote: I do not like it

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

      yes, if your rating is less than 1600 Div 3 contest will be rated for you. but as I can see you are unrated so yes this contest will be rated for you

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

        Hmm, then why am I not rated for this contest?

        Edit: Sorry, I didn't know that it just need to be waited.

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

          Rating gets change after 12 hours of hacking phase, in Div. 3

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

    And I started missing Vova in the contest. Spoiler: https://mirror.codeforces.com/contest/1324/problem/E

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

how can I become a tester?

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4 years ago, # |
  Vote: I like it -64 Vote: I do not like it

Editorial before contest ;)

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

    this ain't codechef! ;p

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

      CodeChef_admin teja349 Look what world thinks about you. Thanks to the long challenge

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

        There is a lot of cheating going on codechef long long challenge.

        Search on Telegram, there a special group ( dont remember exact name but its similar to "codechef discussion" ) dedicated to discuss the test cases and solutions.

        Also on YouTube found some guys explaining the solutions in comment boxes.

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

          I really dont know why u try to blame codechef or codechef admin for such thing. They are just organising contest they are not saying u to cheat and u know what its people like u who cheat in the contest search for links on telegram and so so... and really dont know why people cheat just to gain good rating ... well my friend rating at any platform wont fetch u any job or such its the knowledge that can ... so just stop blaming and start studying

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

          Hell yeah!! The name of telegram grp is exact same. Another reason to scrap long. I saw people there are congratulating each other and saying I got +210, i got +190 blah blah. And when i saw the shared files and photos then i realised how they acheived so. I still remeber codechef used to be good platform but now it is not so, you will barely see any (non indian) suggesting codechef. It can still regain its glory but for that they have to take some serious action and yeah plagiarism detector in long challenge is ineffective as one can easily make changes in entire code as long challenge is very supportive in such case as it give plenty of time

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

            Forget about non-Indian...I barely see any Indian suggesting Codechef nowadays XD...

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

        He's the codechef admin?!!!!!!!!

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

          I tagged codechef admin and cache they are different person. Cache was admin of this contest

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

            Oh I'm sorry.. I didn't notice that was a separate handle..

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

vovuh Will always be in our memory

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

Consecutive div3 without vovuh :|

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

Hope solving upto C will be enough to increase rating for newbies like me :|

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

I wish all rated(<1600) users in this DIV-3 will be Unrated in the next coming div-3 rounds! :-)

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4 years ago, # |
← Rev. 2   Vote: I like it +7 Vote: I do not like it

I'm just curios, did vovuh retire?

Also almost-copy-pasted-part is a lie. :(

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

I have only taken part in one rated contest, I guess this one's unrated for me.

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

    you are rated.. Read the line carefully >> "Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you."

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4 years ago, # |
  Vote: I like it +210 Vote: I do not like it

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

    told ya he needed warm up :))

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

    .

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      4 years ago, # ^ |
      ← Rev. 2   Vote: I like it +22 Vote: I do not like it

      Come on, I am here for a year practising almost every day for months

      Is this how months of practice looks like? There is a reason why people who are green are green.

      Edit: I used Codeforces Visualizer to plot this.

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

        Destruction level 1e9 + 7. xD

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          4 years ago, # ^ |
          ← Rev. 2   Vote: I like it -25 Vote: I do not like it

          .

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

            The graph clearly shows "Your way of practice". Mine is even poorer than yours and I clearly know what my way of practice is.

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

        BTW which website is it ?

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

        Sorry I'm new here. How do I know the rating of a problem? How do I get problems of a particular rating? And how can I access such data for myself?

        Ty :)

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

          Problemset. Here you can filter problems according to it's rating. The filter is on the right.

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

            Thanks! What level of problems should I be solving relative to my rating?

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

              It varies from person to person.Looking at your graph you should probably be trying problems ranging from 1400-1700(same as mine) .If you find it too difficult gradually,come down to easier questions and practice them till you get a firm grip.If you find the questions easily solvable ,move up to higher rated problems.Always remember the key point is solving problems slightly above your comfort zone.You can use various sites like a2oj (https://www.a2oj.com/Ladders.html) and (https://www.a2oj.com/Categories.html) and code-drills(https://recommender.codedrills.io/) to practice as well.

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

        Where can i find this graph for myself?

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

          You have almost the same solve count as me on Stopstalk. But, It's hard to measure the difficulty of those numbers. Try doing more 1400-1500-1600 difficulty problems on Codeforces. By the time you do more than 100 of >=1500 problems, you won't be pupil anymore.

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

    that's great I demoted to pupil

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

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4 years ago, # |
← Rev. 2   Vote: I like it -55 Vote: I do not like it

Always in Div.3 contest

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4 years ago, # |
  Vote: I like it -33 Vote: I do not like it

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

my first div 3 contest as an expert excited

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

    Now you can play without tension...I don't know when I will be a expert

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

No offence .. It's just a meme ..

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

We are missing vovuh

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

    Did you mean the other way around? I guess Vovuh and Stepavly should be swapped in this.

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4 years ago, # |
  Vote: I like it -44 Vote: I do not like it

We are getting almost copy pasted blogs, one day we will get almost copy pasted problems.

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

    yeah you can make your own codeforces for that

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

    I think spending time on problems is of greater importance than spending time on writing beautiful or new blogs

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

RIP — vovuh, heh i will miss your contests(

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

Hope this round will give me positive rating change.

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

    Just make 1 submission (correct or wrong doesn't matter) and then even God can't stop you from getting positive rating change. XD #newratingsystem

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

All Div-3 contests Div-3 Round 1 http://mirror.codeforces.com/contest/977 Div-3 Round 2 http://mirror.codeforces.com/contest/978 Div-3 Round 3 http://mirror.codeforces.com/contest/988 Div-3 Round 4 http://mirror.codeforces.com/contest/999 Div-3 Round 5 http://mirror.codeforces.com/contest/1003 Div-3 Round 6 http://mirror.codeforces.com/contest/1005 Div-3 Round 7 http://mirror.codeforces.com/contest/1006 Div-3 Round 8 http://mirror.codeforces.com/contest/1015 Div-3 Round 9 http://mirror.codeforces.com/contest/1029 Div-3 Round 10 http://mirror.codeforces.com/contest/1066 Div-3 Round 11 http://mirror.codeforces.com/contest/1077 Div-3 Round 12 http://mirror.codeforces.com/contest/1092 Div-3 Round 13 http://mirror.codeforces.com/contest/1095 Div-3 Round 14 http://mirror.codeforces.com/contest/1102 Div-3 Round 15 http://mirror.codeforces.com/contest/1108 Div-3 Round 16 http://mirror.codeforces.com/contest/1118 Div-3 Round 17 http://mirror.codeforces.com/contest/1133 Div-3 Round 18 http://mirror.codeforces.com/contest/1141 Div-3 Round 19 http://mirror.codeforces.com/contest/1144 Div-3 Round 20 http://mirror.codeforces.com/contest/1154 Div-3 Round 21 http://mirror.codeforces.com/contest/1157 Div-3 Round 22 http://mirror.codeforces.com/contest/1165 Div-3 Round 23 http://mirror.codeforces.com/contest/1176 Div-3 Round 24 http://mirror.codeforces.com/contest/1183 Div-3 Round 25 http://mirror.codeforces.com/contest/1196 Div-3 Round 26 http://mirror.codeforces.com/contest/1203 Div-3 Round 27 http://mirror.codeforces.com/contest/1213 Div-3 Round 28 http://mirror.codeforces.com/contest/1216 Div-3 Round 29 http://mirror.codeforces.com/contest/1234 Div-3 Round 30 http://mirror.codeforces.com/contest/1249 Div-3 Round 31 http://mirror.codeforces.com/contest/1256 Div-3 Round 32 http://mirror.codeforces.com/contest/1272 Div-3 Round 33 http://mirror.codeforces.com/contest/1283 Div-3 Round 34 http://mirror.codeforces.com/contest/1294 Div-3 Round 35 http://mirror.codeforces.com/contest/1296 Div-3 Round 36 http://mirror.codeforces.com/contest/1311 Div-3 Round 37 http://mirror.codeforces.com/contest/1324 Div-3 Round 38 http://mirror.codeforces.com/contest/1328 Div-3 Round 39 https://mirror.codeforces.com/contest/1335 Div-3 Round 40 https://mirror.codeforces.com/contest/1343 Div-3 Round 41 https://mirror.codeforces.com/contest/1353 Div-3 Round 42 https://mirror.codeforces.com/contest/1360

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

What does a penalty of 10 minutes mean? If you have a wrong answer submission you lose ten minutes?

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

    The points you lose for submitting 10 min later will be the points deducted for 1 wrong submission.

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

    Let's take an example. Suppose you are submitting your question A after 5 minutes of contest's start time. If it is going to be correct you will be given penalty of just 5(minutes to solve question). Now suppose it is wrong on some test case.You find fault in logic and submit it after 15 minutes from the start time. So total penalty for this question would be 15(minutes to solve question) + 10(for 1 wrong submission)=25. For every wrong submission you will be awarded with 10 minutes penalty. I hope this cleared your doubt about 10 minutes penalty.

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

      You could have simply said that we get 10 minutes behind than the actual submission time.

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

        Well I tried my best to explain him 10 minutes behind the actual submission time.....

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

Live upsolving 5 mins after the round ends: https://youtu.be/Fcxm3iROflI

Good luck!

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

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

    Stfmu!

    Having a good day
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      4 years ago, # ^ |
        Vote: I like it -16 Vote: I do not like it

      My guy almost thought he is going to get +ves for the comment ((

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

        You see LIGHT in my profile pic..?

        YES!! I've always admired THE negative. [wicked smile]

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

    not when u code in python:)

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

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

vovuh will you make div(1, 2) contest in the future??

most of the participants will be looking forward to the contest that you are making.

good luck to everyone who are participating in this contest!!!

and if you are interested and don't know look into it(there is an extension which predicts your score change after contest called CF-Predictor)

(Good luck & high rating!)

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

You have 6 Hrs 30 Min to provide fastest editorial. :)

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

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

I thought vovuh was a university student... Though youth doesn't prevent him from being strong and orzable.

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

    Actually, I am stupid and "high school" was a semantic typo because I don't remember what is high school exactly and of course because I am stupid. Sorry :(

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

    What does orzable have to do with it?

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4 years ago, # |
← Rev. 2   Vote: I like it -59 Vote: I do not like it

Is it rated?

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

waiting for this contest <3

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

Worst Problem Today: CF Predictor is disabled.

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

    I've updated the extension, you probably didn't accept new permission. Please let me know if you have latest version of the extension (1.3.0) it's enabled and still doesn't work.

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

"do not have a point of 1900 or higher in the rating." 1900 or1600?

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

    lets say at some point in time you've been 2000. then you do a huge drop and go to 1200. in this situation your current rating is under 1600, but you have a point in which your rating has been above 1900 and because of that div3 will not be rated for you. hope that helped

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

hope to solve a b c or a b c d

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

Looks like most unbalanced Div 3 ever. Solve first 3 and then netflix and chill.

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4 years ago, # |
← Rev. 3   Vote: I like it -7 Vote: I do not like it

stringforces!

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4 years ago, # |
  Vote: I like it -50 Vote: I do not like it

Worst contest of all time.

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

    same to me..a b solved with 8 min..but c killed me..i solved at last with 6 WA.

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

notDiv3 Forces

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

Comments summarized -
Make Div.3 great again.
Bring vovuh back.

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

    Today's contest was great. wasn't it?

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      4 years ago, # ^ |
      ← Rev. 3   Vote: I like it +18 Vote: I do not like it

      yes but I think problems are more suitable for DIV-2.

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

        Yeah, i agree that problems were tougher than usual Div3's.

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

Could you anyone explain answer 15-beautiful to the task E?

20 10
aaebdbabdbbddaadaadc

Counts:

[a,b,c,d,e]
[7,5,1,6,1]
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4 years ago, # |
  Vote: I like it +1 Vote: I do not like it

As usual xD.D always alot harder than C

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

F1 seems weirdly familiar: https://mirror.codeforces.com/contest/606/problem/C

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

How to solve F1 !?

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4 years ago, # |
← Rev. 2   Vote: I like it +15 Vote: I do not like it

C to D long difference -_-

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    4 years ago, # ^ |
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    Hey, how to upload a meme?

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      4 years ago, # ^ |
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      1. upload image on imgflip.com
      2. you can add some text on the picture.
      3. copy the link and paste in the comment picture option.
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4 years ago, # |
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corner cases in C sucked the crap outta me

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4 years ago, # |
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How to solve C? This one was hard for me

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    4 years ago, # ^ |
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    man are you nude in pic ?? !! hell !!

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    4 years ago, # ^ |
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    1. between two 1 >> count number of zero ..count-=k and ans+=count/(k+1);
    2. and for first until found 1>> count number of zero ..and ans+=count/(k+1);
    3. and for last_1 to last>> count number of zero ..and ans+=count/(k+1);

    4. But if all zero then ans=(n+k)/(k+1);

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4 years ago, # |
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What is this lol?

https://mirror.codeforces.com/contest/1367/submission/84003910

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4 years ago, # |
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I submitted the solution for E here: https://mirror.codeforces.com/contest/1367/submission/84020235 It gives the correct output locally, as well as on codechef's online IDE. What's going on? Can anyone help?

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4 years ago, # |
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Can someone explain their approach to F? I was thinking that the answer is something along the lines of $$$n - LIS(a)$$$ but I couldn't prove it

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    4 years ago, # ^ |
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    Yes we have to find the LIS but it should also be the subarray of sorted version of that array.

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    4 years ago, # ^ |
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    There is one more condition that LIS should be consecutive in given sorted array.

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4 years ago, # |
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vovuh back!""/>

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4 years ago, # |
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Am I the only one who was facing difficulties in implementing D?

I should have tried E first.

Looking forward for short ways to implement D.

PS. Solved D,5 mins before the contest ends. Fingers crossed for system tests.

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4 years ago, # |
← Rev. 2   Vote: I like it +7 Vote: I do not like it

Problem F1 is a variation of this problem: https://mirror.codeforces.com/contest/1231/problem/E

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4 years ago, # |
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The problems were nice!

But the Huge difficulty gap between Problem C and D made the contest "FastTypeForces" !

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4 years ago, # |
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Can Anybody tell that is there any corner case in Problem C? Getting WA on test 2. Solution — 84019963

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    4 years ago, # ^ |
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    Brother your solution is failing on some test cases... One example
    n=5 k=1
    string= 10100
    Your output= 0
    Answer should be= 1 (10101)
    Please check your code accordingly.......

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      4 years ago, # ^ |
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      Thanks Brother for replying,

      I think Answer should be 1. Why are you counting the '1' which is already given? we have to find additional tables that we can occupy.

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4 years ago, # |
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Dont konw why get WA on 3 in problem D until the end of the contest. Interesting maybe I implement something stupidly wrong.

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4 years ago, # |
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Tough div3 round!!

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4 years ago, # |
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I found the answer for F1 as n — (longest sorted subsequence length). Why doesnt the same logic work for F2? My logic was basically keeping the already sorted things at their place and moving other numbers to sort them.

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    4 years ago, # ^ |
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    1

    4

    2 0 0 3

    Longest sorted subsequence is 0 0 3, but you cannot move 2 to the middle in one move.

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      4 years ago, # ^ |
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      By longest sorted subsequence i did not mean Longest increasing subsequence. Sorry for the confusion. What i meant was if we sort the given sequence lets say

      S = 2 0 0 3

      and the sorted sequence becomes

      S' = 0 0 2 3

      I am calling the longest sorted subsequence as the largest subsequence in S which is a substring of S'. So for your example it will be 0 0 and the answer comes to be 2. Again, sorry for the confusion of terminology.

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        4 years ago, # ^ |
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        it will work, your way of finding the lis which occurs as sorted subarray is wrong. let's compress the array so that it contains elements from 1 to n. The problem is when an element(let's say $$$x$$$ and $$$x$$$ -1 is already taken in LIS) has multiple occurences than we need to ensure that if we take $$$x$$$ + 1 then all the occurrences of $$$x$$$ are already taken in LIS. This is the thing you are missing (i too missed this).

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        4 years ago, # ^ |
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        How does one come up with such observation? Its like, I thought of LIS but after seeing the last sample test case I thought may be this observation of mine is farfetched. Do I need to solve similar questions before I get any close to acing div2 and div3?

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          4 years ago, # ^ |
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          https://mirror.codeforces.com/problemset/problem/1363/F

          i couldnt understand the question to the link i gave you, before. Its editorial had similar wording. So while i was trying F i thought of the operation as cyclic shifts and modeled it similar to this question. I remembered in the actual editorial (there was an editorial of this question which i cannot find link to, this question was copied from there). In the actual editorial they talk about if both types of shifts were allowed. So i modeled on that solution. I think in the end it is how many questions you have solved and how much did you learn from them. Keep solving and you will get these questions soon :)

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4 years ago, # |
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StringForcessss

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4 years ago, # |
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bring back vovuh

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4 years ago, # |
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In my opinion too hard problems for div 3 and I felt like it was div 2 with more problems than usual

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4 years ago, # |
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D is for div2

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4 years ago, # |
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Problem F is very similar https://atcoder.jp/contests/agc024/tasks/agc024_b?lang=en , but I can't solve F2 ( ；∀；)

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4 years ago, # |
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How can i solve D and E? I solved A,B,C fast but I can't get an idea how to solve these two

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    4 years ago, # ^ |
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    Problem D

    • Let $$$X$$$ be the number of position $$$i$$$ such that $$$B_i$$$ is $$$0$$$ and $$$t_i$$$ is still undetermined.
    • Choose the biggest character $$$c$$$ such that it is unused, smaller than any already used character and it appears at least $$$X$$$ times in $$$s$$$. Assign $$$c$$$ to all of those $$$X$$$ positions described in the previous step.
    • For all the position $$$j$$$ where $$$B_j$$$ is non-zero, subtract $$$|i-j|$$$ from $$$B_j$$$ for each position $$$i$$$ of those $$$X$$$ positions we got in the first step.
    • Repeat these steps until all the characters of $$$t$$$ are determined.
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4 years ago, # |
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Codeforces should add a new feature for rating a round. from C to D hardness jumped like anything and this isn't good for us. at the last it was just a typing round. maybe testing could have been better.

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4 years ago, # |
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Here's how I solved D:

We have our array b. We start filling our final string at those positions where b[i]=0 {because we can fill all these positions with greatest alphabet having relevant count}. This means, first iterate over string and calculate count of each character in our original string s. Now, at each iteration, we fill all indices at which b[i]=0 with the character that is lexicographically greatest, and has a count greater than or equal to no. of indices having b[i]=0. Dont forget that with increasing iterations, the character in the final string that you fill in at all 'i's such that b[i]=0; should decrease lexicographically.

Also at each iteration, for each index value where b[i]=0; update the values in array b for every j (b[j]!=0) by b[j]= b[j]-abs(j-index[i]) {where lets say index array contains all positions in b where b[i]=0}. This is done to ensure that the contribution of positions we've already filled, is not taken further into account while filling the final string in further iterations.

Do these iterations uptil the level, all positions in the final string are assigned some character.

You can visit my profile and see my code. Its pretty understandable.

Btw It was a beautiful contest. I couldn't have time to solve E although it seemed doable to me.

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4 years ago, # |
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Was E today easier than usual div3 Es?

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    4 years ago, # ^ |
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    slightly but it is ok it was more because D was hard

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4 years ago, # |
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why there are hacks on D?

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4 years ago, # |
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Video Tutorial C:https://www.youtube.com/watch?v=lCNk_D5m6-I

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4 years ago, # |
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LOL F1 was much easier than D,E

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4 years ago, # |
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Ashishgup is back!!

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4 years ago, # |
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Edit: Found a simpler method.

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4 years ago, # |
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I got this diagnostics from my submission 84025940 for 1367D - Task On The Board. Does anyone know what this means?

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    4 years ago, # ^ |
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    The error is in reference with the cf evalutor, read the check log you will get it. Yours code is generating warnings but no compilation or runtime error. The ans it is printing is causing the error in the evaluator

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4 years ago, # |
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F1 is very similar to this problem from SPOJ which I already solved. I didn't read F1 during the contest (thinking it would be very difficult) and now I submitted the same code just with one change and got accepted :-( and F1 is more easier than D and E

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4 years ago, # |
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What's the meaning of giving such useless pretests? Isn't it better to run the whole dataset after the contest and no testcase run during the contest? If pretests of problem D didn't give the AC verdict,I would make some cases and run them for my code. The case missing in the pretest set is like:

1 aaabbc 4 3 2 1 0

Simple and necessary case.

What's the meaning of pretests? mocking?

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    4 years ago, # ^ |
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    Exactly my question. If you don't even care enough to give some critical in pretests what's the use of even giving some of those?

    Many setters even exclude all the critical cases intentionally to make every contestant suffer after the contest ends. I don't actually get the actual reason behind this. Contestants love a contest with some strong pretests, not your silly evil game.

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      4 years ago, # ^ |
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      You should work on testing your own code. TopCoder for example gives very simple pretests. If pretests catch everything, then hacks will be impossible.

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        4 years ago, # ^ |
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        Yeah, I guess. The best thing we can do from our side to write the cleanest as possible code possible, I guess.

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    4 years ago, # ^ |
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    mian hehe

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      4 years ago, # ^ |
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      I have hacked my own submission with this case. I will be pleased to know how the case is invalid.

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      4 years ago, # ^ |
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      You might have given 1 aaabbc 4 3 2 1 0 in the hack. The correct format is
      1
      aaabbc
      4
      3 2 1 0

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    4 years ago, # ^ |
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    The first example case tests the same thing and your code somehow gets marked as OK despite an invalid answer. I don't think the pretests are weak, I think the checker is broken.

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      4 years ago, # ^ |
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      No, I was not taking care of the frequency. Say, I want to put a character in the indexes where b[I] = 0. Let, I have chosen character 'x' and I don't have enough characters to put in the indexes where b[i] = 0. My code was not handling that and got AC. It's not fair at all.

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    4 years ago, # ^ |
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    MikeMirzayanov Stepavly Supermagzzz What the FUCK man. You FUCKING FUCK.

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4 years ago, # |
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MikeMirzayanov Stepavly i wonder how did this pass ? the complexity is O(n*n*n) 84019953

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    4 years ago, # ^ |
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    The sum of n for all test cases in one test does not exceed 3000.

    I THINK its ok with the constraints.

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      4 years ago, # ^ |
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      3000^3 should be TLE :/

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        4 years ago, # ^ |
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        I think it is $$$\frac{3000^3}{8}$$$, which is aprox 3e9 and slightly fits into 2000ms.

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    4 years ago, # ^ |
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    Your algorithm has a good constant factor and TL is quite big.

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    4 years ago, # ^ |
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    it's just O(n*n)

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    4 years ago, # ^ |
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    Maybe it's due to compiler optimization...

    The algorithm is exactly $$$O(n^3)$$$ but the compiler greatly optimized it...

    In fact, that program need to run about $$$4.5*10^9$$$ operations in the worst case (when $$$a_i$$$ is strictly increasing), which should take over $$$20$$$ seconds without optimization :(

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      4 years ago, # ^ |
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      Yes I know that my program need to run 4.5e9 in the worst case .. and i tried to hack it but i couldn't .. so i think that is unfair :/

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4 years ago, # |
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Can any one Explain E problem?

`Thanks in advance`
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4 years ago, # |
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For people who prefer video editorials, I discuss the solutions to all problems at the end of my screencast of the round.

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4 years ago, # |
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I hope "accepted" and "pretest passed" will not follow the rule of social distancing

but vovuh should not keep social distancing from Div3

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4 years ago, # |
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83942386 why is it giving MLE for the first question ????

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4 years ago, # |
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Is there some problem with the checker for Problem D ?
For the case-
aabc
3
2 1 0
Many submissions give "bbc" as output and checker give them Ok response

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4 years ago, # |
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why am i getting this error in trying to hack a solution ? Validator 'validator.exe' returns exit code 3 [FAIL initial string should satisfy distance condition (test case 1) can anyone help ?

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    4 years ago, # ^ |
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    I guess you are talking about problem C.
    From error it seems that that you are entering string that itself is not satisfying the condition of minimum distance. Eg. For n=5 and k=1 you cannot enter input string as 10011

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4 years ago, # |
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why not my dashboard is not showing i have participated in this contest and even not any changes in rating

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    4 years ago, # ^ |
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    i can see you in the standing and wait for rating change.

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4 years ago, # |
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Is the round rated yet?

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4 years ago, # |
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Have all the submission's been re-judged after the hacking phase? it doesn't look like it.

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4 years ago, # |
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My solutions are in queue since 30 minutes!

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    4 years ago, # ^ |
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    maybe server is down,once my solutions were in queue for 4 hours..

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4 years ago, # |
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Hey all, I am a newbie and I saw many blogs about problem D of yesterday's contest . So I want to know that whether this contest is rated for me or not . I am able to solve only problem A and B

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    4 years ago, # ^ |
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    Rated for you.rating change doesn't not related with newbie or you saw problem D in many blog..rated for all are rating less than 1600.

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      4 years ago, # ^ |
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      Ok fine but why till now no improvement in rating. Is it unrated ?

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4 years ago, # |
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Hey i gave this contest and my rating is not updated yet I am new to codeforces how much time it takes to update rating??

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4 years ago, # |
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solved E without graphs.. gcd and some basic operations : solution

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4 years ago, # |
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Why has the rating not updated yet?

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

In problem D, there was an issue in the checker program, which affected some participants. I am now investigating this incident. I'll exclude from the rating all those who were affected by this mistake. During the research, I will temporarily hide the problem from the contest, then it will return. I believe that the problem affected no more than a few percents of all participants in the round. I apologize: I was one of three people who read the checker but did not notice a typo in it.

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    4 years ago, # ^ |
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    But pls make sure those who have submitted correct , they should be rated with problem D,because i see a sudden drop in my standing

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      4 years ago, # ^ |
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      Yes, the people who submitted it right must be given points for it and the system testing should be done again.

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      4 years ago, # ^ |
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      Same thinking with you :(

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      4 years ago, # ^ |
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      What's actually a hacking phase in codeforces? I'm new at it and I've seen people talking about hacking a problem or solution (don't know exactly what it is). Can someone explain about it little bit?

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        4 years ago, # ^ |
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        After the contest is over, your solution can be viewed by anyone. You can then run the solution on your custom testcases known as hacks. if the solution fails, then the hack is succesful.

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          4 years ago, # ^ |
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          Wait but if the code fails on someone's custom testcases then how did it pass the codeforces' test cases in the first place?

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            4 years ago, # ^ |
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            During a live contest, your solution is not tested on all the testcases as it will increase judging time. So a small number of strong testcases called pretests are used. But sometimes the pretests turn out to be weak.

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      4 years ago, # ^ |
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      Bro it's hide the problem temporarily only. After research were complete it again return it

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    4 years ago, # ^ |
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    Will the ratings update be delayed because of this?

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    4 years ago, # ^ |
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    MikeMirzayanov, if my D was hacked because of the issue with the checker, I don't think the contest should be unrated for me because I spent two hours on the contest from my valuable time. Please consider the D as a wrong answer just like any other hacked answer and rate the contest for the affected people. I worked hard for all the problems and I am sure so did the other affected people.

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      4 years ago, # ^ |
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      I agree. The decision doesn't seem fair to me.

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        4 years ago, # ^ |
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        For the first time, I was on the verge of becoming an Expert and now, I am unrated in the contest. This is largely unfair. I request the organizers MikeMirzayanov and Stepavly to please reconsider.

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      4 years ago, # ^ |
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      After solving A B C pretty fast if I had left D i would have gained aroung 50 but for trying D and almost solving it (just missing the frequency check) the contest is unrated for me. Doesnt seem fair.

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      4 years ago, # ^ |
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      Have they made it official that the contest is unrated? If so, then could you please provide me a link or let me know where you found it?

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        4 years ago, # ^ |
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        My account is missing from the standings. So are the ones who did D wrong.

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          4 years ago, # ^ |
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          same here!..This is totally unfair. Just treat the prob D as the wrong answer and make the contest rated.

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      4 years ago, # ^ |
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      How you can be unrated for problem D , that you did not solved yet.. just wrong answer on test 1. my friend Adicr7 also got WA on 2 but he is still rated..your on may be other reason ..

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    4 years ago, # ^ |
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    This seems quite unfair to me, as I solved A,B and C fast. Although D solution was hacked, but still my rating would have increase. But suddenly, now I am unrated for the contest.

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

Please explain me where problem D is ??

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

    In problem D, there was an issue in the checker program, which affected some participants. I am now investigating this incident. I'll exclude from the rating all those who were affected by this mistake. During the research, I will temporarily hide the problem from the contest, then it will return. I believe that the problem affected no more than a few percents of all participants in the round. I apologize: I was one of three people who read the checker but did not notice a typo in it.

    -MikeMirzayanov

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

    Can you read a few comments up?

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

    _Tien_ See MikeMirzayanov's comment here

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

Why is the problem D removed?

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

    Read a few comments up

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

      I wonder why would anybody post such a question without checking the comment section for the answer first.

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

        extremely sorry I didn't see the above comments, will take care next time onwards

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

    Read comments above you.

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

    There is a problem with the checker For the case- aabc 3 2 1 0 Many submissions give "bbc" as output and checker give them Ok response

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

This was my first contest on codeforces, but its not showing any rating for me?

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    4 years ago, # ^ |
    ← Rev. 3   Vote: I like it +18 Vote: I do not like it

    You have to wait(This is not atcoder). I guess it will be updated within an hour.

    Upd: I was wrong. 1 hour has passed. But not updated yet.

    Upd2: 2 hours!!

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

    Because ratings are not updated yet.

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

how much more time will it take for rating to show

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

Hope problem D will return soon.:D

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

    Already returned...

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      4 years ago, # ^ |
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      I'm sorry. :(
      I just learned the issues about problem D a few minutes ago and didn't notice that.

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

When the ratings will be updated ...

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

    Same here, I hope it's going to happen soon

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

One of my friends solved 5 problems and rating predictor was showing +139.Later his D got hacked.still rating predictor showed +58.Now this round is unrated for him.This is so pathetic.

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

Don't know why but my rank is just toggling between 558 and 670 every time I refresh, looks like rankings have not been finalized yet

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

[sheeeeeeeesh]

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

    Can you say it in a way that everybody understands?

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

    I understood.Actually large amount of pretests create long queues for that reason the time needed to show verdict becomes too long.But setters want to set strong testcases so that it may pass system test.But it is completely your misfortune to get wa or tle or some other verdict except accepted after system test or hacking phase.

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

hi i want to tell that "rishab1815" mushkilWaqt_CommandoSakt and "Rishabsoni1815" Rishabsoni1815 are both my accounts

Attention!

Your solution 83955381 for the problem 1367B significantly coincides with solutions rishab1815/83955381, Rishabsoni1815/84010648. Such a coincidence is a clear rules violation. Note that unintentional leakage is also a violation. For example, do not use ideone.com with the default settings (public access to your code). If you have conclusive evidence that a coincidence has occurred due to the use of a common source published before the competition, write a comment to post about the round with all the details. More information can be found at http://mirror.codeforces.com/blog/entry/8790. Such violation of the rules may be the reason for blocking your account or other penalties. In case of repeated violations, your account may be blocked.

please see in this matter @codeforces MikeMirzayanov

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    4 years ago, # ^ |
      Vote: I like it +44 Vote: I do not like it

    You cannot use multiple accounts in a contest.This is a violation of contest rules

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    4 years ago, # ^ |
      Vote: I like it +59 Vote: I do not like it 
    The registration confirms that you:

* have read the contest rules  by the links http://mirror.codeforces.com/blog/entry/456 and http://mirror.codeforces.com/blog/entry/4088
* will not violate the rules described on http://mirror.codeforces.com/blog/entry/456 and/or http://mirror.codeforces.com/blog/entry/4088
* will not communicate with other participants, share ideas of solutions and hacks
* will not use third-party code, except stated in http://mirror.codeforces.com/blog/entry/8790
* will not attempt to deliberately destabilize the testing process and try to hack the contest system in any form
* will not use multiple accounts and will take part in the contest using your personal and the single account.
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4 years ago, # |
← Rev. 2   Vote: I like it -13 Vote: I do not like it

i have two ID on Codeforces. Unfortunately, I have submitted solutions of a contest from both of my id and hence, I got an email regarding clash of solutions. What should i do to prevent both of my ids from being blocked??

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

    Now you have to suffer for your deeds.

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      4 years ago, # ^ |
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      So, what will be the severest result?

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

        it may happen definitely that one of your account will be blocked or also possible that both of your account. Don't go blindly for ratings , make yourself a good coder ...

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

    If you have done this for first time,your id will not be blocked.But repeatedly doing this may result in blocking or some other severe punishment.

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      4 years ago, # ^ |
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      all of my submissions were skipped....

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

        This time you will only get skipped. But the next time your ids will be vanished.

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

[Now Changed]

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

    [Not Changed]

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

      Some people faced hack on D and in the last they became unrated. I know , some of them solved a b c very fast and will get + rating. But think logically if judge them just skip D who faced hacked on D, some people get — rating for only system problem..So some people always faced unfair. GL and hope for your best..

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

        Yes, but whenever there was a problem in tests or something else, the round became unrated. Now they simply crossed out a layer of players indiscriminately. A strange decision, it was possible by individual decision of the participant to remove or not remove him from the competition

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        4 years ago, # ^ |
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        And what's more — my decision D wasnt hacked — it didnt pass the final tests.

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          4 years ago, # ^ |
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          i feel your pain bro. I think you will back to be more strength full and do good. GL & take love

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4 years ago, # |
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my rating is 1328 but i am newbie , I want to know the boundary of pupil. Please tell me

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4 years ago, # |
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Can anyone tell me why my rating is not updated? My solution to problem D was Hacked(Is is the reason?)

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

    Yes

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

      Hacking a task is the reason that the rating will be given less, or it will be removed altogether, but it`s not the reason for removal from the list of participants, most likely it is a system bug, task D either disappears, then appears, and problems arise in people who decided or tried to solve D

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

    contest is declared unrated

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      4 years ago, # ^ |
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      Is is unrated for only those whose problem D got wrong?

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

        Yes...whose problem D was wrong first then got accepted or got hacked...or those who hacked solutions for problem D

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

I am in position 3670 with ABC solved and I got rating update from 1217 to 1263. In the same position 3670 with ABC solved, another one got update from 1227 to 1339. Can anyone explain this system?

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

@MikeMirzayanov i participated in this round but my rating is not updated.

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

I registered and participated in the contest but my rating didn't change . After the problem D came back to rank list I was removed from the official rank list . Why ? Please anyone tell me. @MikeMirzayanov

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

Could someone please help me figure out the error in my code? https://pastebin.com/wvfqbw6Z Fails a particular case in test case 2.

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

    It would better if you'd share the link to your failed submission (instead of pastebin). It would at least be clear what problem you are talking about.

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

    on line 34 (without comment-i just count from up)

    need to change from>>> l = one_pos[0] — k — 1; //left free length to >>> l = one_pos[0] — k; //left free length

    ** just need to remove -1 .. i think you did it mistakenly..

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

lol.I just deleted from the final results. They didn’t even give a rating. WTF @MikeMirzayanov:D?

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

    In problem D, there was an issue in the checker program, which affected some participants. I am now investigating this incident. I'll exclude from the rating all those who were affected by this mistake. During the research, I will temporarily hide the problem from the contest, then it will return. I believe that the problem affected no more than a few percents of all participants in the round. I apologize: I was one of three people who read the checker but did not notice a typo in it.

    -Mike

    I guess all participant with wrong submissions(accepted initially) for problem D along with the hacked ones are removed from official rank list. And rating has been updated for the rest of the participant.

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      4 years ago, # ^ |
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      well well well. I solved 3 tasks. I took the 900 place.I had to get 45 to the rating. And i was kicked? Really? While the rest of the participants got their rating? Very nice idea.Bravo

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4 years ago, # |
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Why my rating is no change? My rating less than 1600, but now my rating is no change!

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    4 years ago, # ^ |
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    My rating did not change either. Someone tell me that post here #bugyforces , I don't know if it is a joke, but there's nothing to lose, I think...

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

Isn't problem 1367F2 - Flying Sort (Hard Version) too similar to 1223D - Sequence Sorting? I got AC on the easy version by just copying the solution of 1223D.
Submissions: 72059675 84097673

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

Why I'm not in the rank list? My rating didn't change either.

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