csacademy's blog

New Online Judge Platform — csacademy.com
By csacademy, 9 years ago, In English

Hello, Codeforces!

We are glad to invite all of you to test out our new Online Judge platform at csacademy.com. We're a Romanian based start-up that focuses on online education. Up until this point we've been working on creating a new environment for competitive programming contests.

Our first beta round took place in January and it was an IOI-style contest of medium difficulty. You can have fun solving the problems in our archive. Pay attention though, it is necessary to have an account in order to solve any problems on our website. You can connect via Facebook or Google+, or you can simply create a new account by providing a valid email address. Once you have an account you can choose a username, but all Codeforces handles are already reserved (so no tourist for the locals :D). We have created for you the possibility of connecting your Codeforces user here. Once connected, your Codeforces handle becomes available, otherwise it stays reserved for an indefinite amount of time.

Our second beta round will take place on Friday, Mar/04/2016 17:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous round, the difficulty will be moderate (similar to a Codeforces Div. 2). You will have to solve 6 problems in 2 hours and 30 minutes.

This time around the format of the round will be different:

  • There will be full feedback throughout the entire contest.
  • Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
  • Tasks will have dynamic score. According to the number of users that solve a problem the score will vary between 100 and 1000.
  • Besides the score, each user will also get a penalty that is going to be used as a tiebreaker. The penalty is computed taking into account the minute of the last accepted problem and the number of wrong submissions (only submissions for accepted tasks count).

More about our platform:

  • For the best user experience we recommend using Google Chrome. We are still in beta and we didn't have time to check if everything works on other browsers.
  • We currently support C++14, Java8, Python2 and Python3. We recommend using only C++ and Java for a contest, as the time limits are not calibrated for Python.
  • We have a pretty cool online editor. We use it ourselves, so give it a try ;)

If you find any bugs please email us at [email protected]

People currently involved with CS Academy include:

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial is ready. Congratulations to all the users and we hope you had a great time. Beta round 3 is around the corner, keep your fingers crossed!

EDIT2: We're hosting Beta Round #3.

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Comments Comments (100)
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9 years ago, # |
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Once you have an account you can choose a username, but all Codeforces handles are already reserved

Why? :(

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

    We did this so that people already known to this community and their friends by a certain name can automatically claim it. Users can claim their Codeforces handles from their profile page. Unfortunately, some usernames (any starting with a non-alphanumeric character) are not allowed. Sorry about it. We can manually link some usernames if you make a good case for it. Email us.

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      9 years ago, # ^ |
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      Account settings page is empty for me

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        9 years ago, # ^ |
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        What browser do you use?

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          9 years ago, # ^ |
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          Chrome on Ubuntu (but it's some old version)

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            9 years ago, # ^ |
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            I've sent you a private message.

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      9 years ago, # ^ |
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      Ah, now I understand! I thought reserved means that they are forbidded for anyone (even the coders who own them) :)

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9 years ago, # |
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why i cannot see any problems in past contest ?

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    9 years ago, # ^ |
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    Unfortunately you cannot read any problems if you are not logged in.

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

      what is the point of this feature ?

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

Using Codeforces to popularize its competitor....shrewd.

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

    Nothing can beat Codefoces.Even Topcoder fails to beat us ;) Codeforces is the best. No doubt at all <3

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

      We're not trying to beat Codeforces, we just wanted to create a platform based on our personal needs.

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        9 years ago, # ^ |
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        yeah, I know. Best of luck :)

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

        personal needs? For example? I just want to know, why people need so many online judge platform, as we notice that the number of OJ is increasing day by day?

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9 years ago, # |
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it would be really cool if workspace opened with user's program template already typed in it.

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

    We'll implement this soon, it should be done by round 3.

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

Just registered. Look like will have fun :)

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9 years ago, # |
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Even after logging in All i see are empty pages . I use chrome on windows 10

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9 years ago, # |
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I use Internet Explorer 11 and have same problem as SarvagyaAgarwal

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

So, what is the difference of your platform and codeforces (or similar ones)?

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

    We're planning to concentrate more on the educational aspects. We have created some interactive lessons, but we haven't made them public yet as we had to prepare these two rounds. We'll get the lessons up and running next week.

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

Seem cool,hope to have fun together.

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9 years ago, # |
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Looks Okey . And Interface is also good . Hope to have some nice problem and to have a Nice Contest to all the Registrant . I am hoping to have some new experience specially about the Dynamic Scoreboard .

All the Best & Keep it Up . It is a great Initiative .

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

Are the contests rated? JK, JK before all the downvotes come.

I really like the interface. I am a high school (ages 13-18) CS teacher, and am very interested in watching this project grow and see if it would integrate into our competitive programming course.

Good luck!

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

    We have a rating algorithm, but we are still tuning the constants behind it. This round will be a great opportunity for us to test the algorithm.

    So yes, this round will be rated retroactively.

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      9 years ago, # ^ |
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      I wasn't really concerned about that. It just seems like everyone here wants them to be rated but honestly what does a rating mean? I don't care.

      What I really would like to see from this, and I don't know if this is what you are planning, but a way to look up a tutorial of a concept and a ton of problems that you could do on that topic. All ordered in a way that matches how it was explained and slowly require students to make small adjustments then when they are making pretty large adjustments or combining things.

      Atleast that is the site I would like to find for competitive programming.

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

        That's exactly what we're aiming for.

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

Russian conditions problems? I'm google-translate-man.

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

    Unfortunately we don't have translate support yet (not even for our native language, Romanian). Hopefully in the next year or so we'll be able to add multi-language support. Russian is first on the list.

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

Just want to point out how cool it is that the CF site put this post on the front page, it really goes to show how they care more about the coding community that just say themselves. I feel that a lot of other places would not allow other sites/people to promote themselves, for instance I don't think topcoder would ever put post about another independent site on its front page. So it is very nice that we have CF as an nonprofit site that does not care about making money and all that, allows everything to be much more objective that way.

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9 years ago, # |
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Seems interesting, I will give Iit a try :D

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9 years ago, # |
← Rev. 2   Vote: I like it +42 Vote: I do not like it

It's really cool of Codeforces to share other contests' websites. It shows how Codeforces is not commercially oriented but rather trying to be helpful and supportive to the competitive programming community.

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9 years ago, # |
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I want to change my handle to ATofighi (It's was my old handle) in your site... How can I do it?

Thanks

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

    We manually changed it for you. Please check if everything is ok.

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

Thank you Codeforces and MikeMirzayanov for all the help. Your support for the community is greatly appreciated.

Starting yesterday we've had a large number of new registered users. Actually, there have been so many new users that we decided to migrate to a new server. It might take a while for the DNS to update, so you might experience problems trying to access csacademy.com for the next half an hour.

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9 years ago, # |
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It would be cool if you could also link the Codeforces handle to the Topcoder handle.

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    9 years ago, # ^ |
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    We wanted to do that but in the meanwhile TopCoder decided to remove the private message functionality. If you have any idea how to check account ownership please let us know.

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9 years ago, # |
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why all pages are blank ??

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9 years ago, # |
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I registered and it only asked my email for registration. I confirmed the email and signed out. Where is the option to set a password?? I cannot sign in using that email again

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    9 years ago, # ^ |
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    You can reset your password.

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      9 years ago, # ^ |
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      Ok. But why didnt it ask for a password the first time i signed up? Its weird

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        9 years ago, # ^ |
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        You are asked for the password only after your email is verified. We're still working on our user flow.

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9 years ago, # |
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Is it possible that out-of-contest submissions can be implemented?

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    9 years ago, # ^ |
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    We'll add the problems in the archive when the contest ends. During the contest you can read the statements but you cannot submit unless you are registered.

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

Всё ровно CF лучше

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    9 years ago, # ^ |
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    Никто и не говорил, что он хуже.

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9 years ago, # |
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No content in the contest page.

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9 years ago, # |
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I was sign in with Google chrome, i also register Arhiva & round 2. but i cann't see any thing in Arhiva aslo in round 2 page...

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9 years ago, # |
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We're really sorry for all the users who cannot access our content. It's a browser compatibility problem that we're not going to be able to solve in time for the contest.

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

In case anyone has the same problem as me: (for me) under linux it's not working under either firefox or google chrome but it's working under chromium.

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9 years ago, # |
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What browser do I have to use to access the contest? I want to take part.

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    9 years ago, # ^ |
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    A new version of Chrome will do.

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

Nice problems, and the site worked perfectly, it didn't shut down, I expected it to as this was the first contest with such registers, i hope it will grow up more and more...

Waiting for Beta Round#3 ^_^

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

    Indeed, really nice problems. I enjoyed the contest a lot!

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

      Yes it was...

      I liked the "run examples" button, it's really helpful, especially when you have large input.

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9 years ago, # |
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May I submit the problems after the contest? I haven't noticed such opportunity.

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    9 years ago, # ^ |
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    You can find all the tasks in the archive.

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

      Thank you! Words of gratitude for the contest and your work! I really admire your site. Wish you an enormous inspiration for a fast improvement and developing!

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9 years ago, # |
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How to solve Lightbulbs

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    9 years ago, # ^ |
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    The editorial will be published in a few minutes.

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

    I don't know how to prove it, but I found the pattern by doing a DP and trying out a few test cases. Add to a vector all the bits that are turned on in the initial state (count bits from left to right starting with 1). Then for every bit 'b' in that vector, add 2b - 1 to the answer if position in the vector is even, or subtract it if it's odd.

    I'd like a proof though.

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9 years ago, # |
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Interesting problems and amazing visualization tools, never seen such things before! Thank you for your work! I am wondering how to view other's code after the contest?

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    9 years ago, # ^ |
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    Thank you very much! Unfortunately you can't see other's source code for now. Still working on it.

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

Thanks! Really nice contest. System worked really fast, never seen that before. UI is pretty cool too. Keep working guys! =)

Waiting for updates and third beta-round =)

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

    Thank you and congratulations! We're happy you enjoyed it.

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9 years ago, # |
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I checked the scoreboard at the end of the round and i was fifth, the penalty for wrong submissions was 25 minutes.

Now i checked i am 7th with 10 minutes penalty for wrong submissions.

My handle on the scoreboard is Ahmed Ossama.

Was the penalty for wrong submissions changed after the contest or did i miss anything?

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

    Initially the penalty for a problem was log2(no_of_bad_submissions) * 25. We changed it after the contest to log2(no_of_bad_submissions) * 15. We decided that 25 was a bit too harsh. We hope these kind of changes don't bother you so much, as we are still trying to find the best constants.

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9 years ago, # |
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wow :D Awesome experience :D

I enjoyed the contest very much :)

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9 years ago, # |
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I only had like 10-15 minutes to be in the contest, but looking at your website, it sounds really cool, I'll be sure to participate in your future rounds.

Note: Safari on OSX does not work. ( it gives a blank page on everything except the homepage). Yet it works perfectly on chrome.

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9 years ago, # |
  Vote: I like it +33 Vote: I do not like it

Since this was beta, I'd like to give some feedback:

  • First of all, thanks for the contest, it was really good!
  • I tried the online editor and I liked it, keep it up! The visualization was nice, although it seemed useful only for lightbulbs.
  • The last line of code is inaccessible to the mouse because it's under the editor buttons.
  • The stderr tab refreshes only after click in it, before that it shows data for previous run.
  • If test 1 passes and test 2 fails it's hard to debug. Writing to stdout causes test 1 fail (so test 2 is not ran) and stderr doesn't show for sample tests. I had to copy the testcase and run it as custom.
  • As someone mentioned, that would be nice to have code template already loaded but that's not a priority.
  • At compilation I get warnings for unused result of scanf. They are not useful and only make compile error list longer and harder to read. I recall there was a flag to g++ to remove these warnings, however I can't find it now.
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    9 years ago, # ^ |
      Vote: I like it +13 Vote: I do not like it

    Also I found that when you type in a question, you cannot delete what you have written i.e the backspace button does not work.

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

    This is such great feedback! Thank you!

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

      After thinking a bit I can also list a few things that would be nice to see (but definitely not a must):

      • Allow adding custom testcases (with expected answer) to the sample tests list. I mean, let them all be available by just one click.
      • Make some defense against missclick submit. The buttons are quite close. One idea is to run samples first and if they fail don't count this for penalty. This would also help those who use local editor and for some reason the outcome is different on their machine.
      • That would be nice if I could run my solution (at least the samples) from keyboard shortcut.

      And one more small issue I forgot: hovering over almost any area in statement/workspace results in a "task" label, which is a bit annoying, especially when it covers text.

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

        We do already run examples first and do not count the submission if your solution fails on those. Thank you again for your feedback! We will do our best to solve those bugs and implements the features you requested.

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

Circular Subarray

How to solve this problem ..??

My idea is to find the sums for 1 — N of K Contiguous element circularly . Then sort the results & find out the median elements as Target sum . Now Subtract other Sums from this Target Sum and Add this Absolute values as Answer .

But through this I found my first & last sample are correct .. Other two test does not give the right Answer . Here is My Sample C++ Code

I don't understand the Test 2 & 3 in the problem set . How they are 12 ( 2nd ) & 6 ( 3rd ) ??

Can someone please help me . It'd be a great favor .

Thanks in Advance .

UPD : I figured out the technique of Test Cases but can't solve it .

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

    My solution uses the idea that 2 consecutive ranges of K elements need to have equal sum, which means that Ai = Ai + k for all i. So we can divide the elements into components, with a DSU for example, and then the problem is reduced to making all elements in each component equal.

    I didn't exploit the fact that the best answer for each component is the median, like the editorial says, so since the function decreases and then increases, I ended up doing a ternary search for every component.

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

I can't enter the account settings page on Safari

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9 years ago, # |
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I wish I could see the results of all tests...

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

Wow! Such positive feedback! And useful features too, like code editor, run examples,etc. Must register now! Two great OJs can co exist in harmony I suppose.

Registered. Great UI!! Keep it up! Kinda felt like you've taken the best of all worlds, but who cares! Its really damn user friendly. :D

Can I suggest something? In c++, please change the default template to 

#include<bits/stdc++.h>
using namespace std;

int main()
{
   return 0;
}
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9 years ago, # |
  Vote: I like it +8 Vote: I do not like it

I love the "Simulate the problem here" section <3!!
Thanks a lot!

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

for Matrix Exploration is the intended solution O(nm)? I have a O(knm) but I can't understand why it gets TLE, when knm ≤ 500 * 106. What are the specifications of the machine that runs the final tests?

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    9 years ago, # ^ |
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    as I know , with our computers(+ online judges) about 10^8 operations take 1 second to perform.so it is not surprising to get TLE.

    If you think more about how bfs works , you can change it a bit to reduce your solution to O(nm).

    ( sorry for my poor english )

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      9 years ago, # ^ |
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      Thank you for your response.

      I modified my BFS so that we have k queues, one for every center, and visit the entire matrix by making one step for every queue at a time.

      My solution was accepted, however I am not sure about one thing. I have a global visited array declared like bool vis[500][1000][1000]. If a bool is 8 bits, then this array requires 500*1000*1000*8 bits, which is around 500 MB. Shouldn't that give problems with the memory or I am missing something? It says that maximum memory usage is 46 MB.

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        9 years ago, # ^ |
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        No , you are right. C++ optimizer is very powerful and maybe it did some magics! (I asked from my friend).

        I appreciate your fast action.

        Actually you don't need k queues and such large array.

        as you know, BFS begins from start position and first see all places with distance 0(start) , then 1 , 2 , ... So here, you have more than one start position with distance 0 and you can have just one queue that contains all special places initially.

        also sharing all visits in one array can't cause any problem so vis[1000][1000] is enough.

        my code

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

I couldn't see tasks or contest dashboard even my account settings ! all pages are empty! i check this with 2computers and many times :(

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    9 years ago, # ^ |
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    Use google chrome

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      9 years ago, # ^ |
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      I use Ubuntu 14.04 could it be a reason for my problem ?!1.

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        9 years ago, # ^ |
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        I use the same operating system. The browser is the problem.

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9 years ago, # |
← Rev. 2   Vote: I like it -18 Vote: I do not like it

Hey, great site but I don't like how a bunch of tasks are impossible or much harder in Python because Python runs a bit slower. Can you please check that all tasks are possible to 100% solve in Python? If not then maybe increase time for Python slightly? Thanks

Edit: Really unfair that I got downvoted so hard (-18) for this, I'm top ten on the site and I enjoy using the site, I just want to be able to use it in one of the 3 languages that they offer. Sigh

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    9 years ago, # ^ |
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    Indeed, we will try to make Python usable some time in the near future.

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9 years ago, # |
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Nice judge, good work guys. Solved addition and gcd :D

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

Very nice platform with very interesting problems. I love the website because it is the only place where you can plot a graph or check your ideas on custom made animations. For further information you can try the last 3 problems from Beta round 2.

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