### slycelote's blog

By slycelote, 11 years ago,

(This FAQ may be outdated. Please refer to official help).

I'm sure we won't need this post after Codeforces comes out of beta, but meanwhile it could be useful :) Feel free to suggest what should be added here.

### Competitions: general

Q. What are the rules of these contests?

Q. What languages are supported? What are the compiler options and run command lines? What is the configuration of judge servers?
A. The judge machines are Core 2 Duo, 2.67 Ghz (E6750). The full list of supported languages and compiler options can be found in this post

Q. How do I hack other's solutions?
A. First lock your own solution in the main ('problems') tab. Then in your room double click or Ctrl+click the solution you want to hack. Check this post for complete rules concerning hacking.

Q. How is rating calculated?
A. The rating system is described in these two posts. Note that even for a joined contest the rating updates are calculated separately for the first and the second divisions. Therefore, a situation is possible, when a div2-coder performed worse than a div1-coder in the same contest, but gained more rating points.

### Competitions: writing code

Q. How do I read/write 64bit integers in C/C++?
A. If you submit under "GNU C++" or "GNU C" option, use this:
printf("%I64d\n",n);
but NOT this:
printf("%lld\n",n);

If you submit under "MS C++" option, both variants should work.

And of course, with C++ you can always write
std::cout << n << "\n";

Q. How can my program determine whether it runs in Codeforces server?
A. For most programming languages Codeforces environment defines the symbol ONLINE_JUDGE. Again, see this post for details.

### Using the site

Q. How do I read other people's code?
A. After the contest is over, go to its page (for example, http://codeforces.com/contest/15 ) and click on this picture: . You will see a page with several submits (currently 100, I think). You can sort and filter the solutions there. To see the fastest solutions, you need to manually paste a URL like this: http://codeforces.com/contest/15/status/A?order=BY_ARRIVED_ASC
(currently there's no way to do this via UI)

Q. During the practice, can I see the test case that my program failed on?
A. No. YES! Go to 'My submissions' tab and click the link showing the ID of your submission.

Q. How can I find some useful information on this site?
A. Try google or this query: "http://codeforces.com/search?query=<what do you want>".

Q. Why are my comments / post empty?
A. If you used copy-paste, your comment may have some incorrect tags. Try to look at the HTML code of your message (button "< >") and erase all charset tags. If the system tells you "Rendering to html failed: ....", you used "\$" symbol. Codeforces supports Unable to parse markup [type=CF_TEX] formulas which are enabled by this symbol. Try to avoid it. Q. Can I post a highlighted code sample? A. Currently the best way is to submit the code to a service like codepad.org and post only links to the submit. ### Miscellaneous Q. I've found a bug! When I upvote a post, its rating increases by 2 points, but when I downvote a post, its rating decreases only by 1 point. A. It's not a bug, it's a feature. • +14  11 years ago, # | +12 Q3. Should I do anything special right after a contest starts?A3. Yes, you should. Open all problems in different browser tabs as soon as possible.There is a good chance you won't be able to do that later, because of the server's occasional shutdowns.:) •  11 years ago, # ^ | +12 Ouch, that was tough! :)But seriously, it happened only twice, I think. (Although I usually try to follow this advice anyway :) ) •  10 years ago, # ^ | 0 I think uploading the problem as pdf on a different server was a good idea :) •  10 years ago, # ^ | 0 Yep, now it seems to happen more frequently :)  11 years ago, # | 0 Wrong.Q2. How do I read/write 64bit integers in C (GNU/ mingw)?Q3. How do I read/write 64bit integers in C (MSVC)?Q4. How do I read/write 64bit integers in C++? •  11 years ago, # ^ | 0 It seems that with GNU C we should also use %I64d, at least here on Codeforces.  11 years ago, # | 0 Actually, "%lld" works perfectly fine, if you submit using "Visual C++" instead of "GNU C++", and I believe is should be mentioned. •  11 years ago, # ^ | 0 So, %lld works iff you submit using "Visual C++", and %I64d works iff you submit using "GNU C++", right? •  11 years ago, # ^ | +1 Most likely for Visual C++ both of them work fine.For GNU only I64d.  11 years ago, # | +3 A2. There's big performance difference between std::cout << std::endl; and std::cout << "\n"; The first statement flushes output buffers to disk, so it is much slower. It matters if output is huge.  11 years ago, # | 0 A4. No. But you can see the number of test on which your program failed.[rus_spoiler]Думаю ещё стоит описать особенности системы комментирования: символ ^ и backspace (browser.back) для возврата на предыдущее сообщение.[/rus_spoiler]  11 years ago, # | +1 Please, add that the judge machines are Core 2 Duo, 2.67 Ghz (E6750). •  3 years ago, # ^ | 0 Is the configuration upgraded or is it still the same? •  3 years ago, # ^ | +1 From https://codeforces.com/blog/entry/8457 they are using i5-3470, but that is also kind of outdated. I'm pretty sure they use some sort of dynamic cloud system now.  10 years ago, # | ← Rev. 2 → +8 Q9. How can I find some useful information on this site?A9. Try google or this query: "http://codeforces.com/search?query=".  10 years ago, # | +4 Q10. Why are my comments crashed?A10. If your comments suddenly disappeared, you used copy-paste and your comment have some incorrect tags. Try to watch html code of your message (button "< >") and erase all charset tags. If system told you "Rendering to html failed: ....", you use "\$" symbol as a symbol. Comments can contain some formulas () with help of "\\$" symbol. Try to avoid this symbols.
 10 years ago, # | ← Rev. 2 →   0 Q0. What are the rules of these contests?A0. Read this.
 10 years ago, # | ← Rev. 2 →   +3 Q. Hi! I'm new at this site. What can I do?A. Here is some tactic:1. Solve the Problemset starting from most solvable - seems to be a more simple problem.2. Wait for a registration for a next contest.3. Register, check yourself in registrants ().4. Wait for the contest starts, read the original interesting contest rules, don't get confused with them, read the rules again.5. Write the contest.6. If you are not in «Top rated», goto step 1.7. ???????8. PROFIT
 10 years ago, # |   0 Q. I want to post all my templates for sharing my beautiful code. Can I do that at this site?A. Yes (?), but you should better post your code on one of the services like codepad.org and have just one post, containing your templates, e.g.:
 10 years ago, # |   0 Thanks for the contribution everyone. Sorry for the delay, I don't receive e-mails about new comments for some reason.
•  10 years ago, # ^ |   +3 Can you translate it into russian?
•  10 years ago, # ^ |   +6 Nope, I'm too lazy to maintain both versions :)
 10 years ago, # |   0 How can I ask a question about a problem that is used already in a contest?
•  10 years ago, # ^ |   0 I think that the best way is to write about it on your blog or find the blog with this particular contest and ask your question there.
 9 years ago, # |   0 Is it possible to change the handle? It'd be nice if I could change it to my Name+Surname making easier for my friends to find me.
•  9 years ago, # ^ |   0 Yes buddy I can understand you It's too bad.. It must be fixed
 9 years ago, # |   0 When I registered for the Contest but at the time it due, I'm busy and can't not attend, will it affect my rating? (I mean will it count as I solved zero problems?)
•  9 years ago, # ^ |   0 No, it will not affect your rating if you haven't done any submitions.
 9 years ago, # |   0 Do you know what is contribution I really need to know that...
 » 7 years ago, # |   0 How could I get problemset which are get input and output from a txt rather than standard input and output...?
•  » » 7 years ago, # ^ |   0 You can't.
 » 6 years ago, # |   0 testing
 » 5 years ago, # |   0 how to raise a help query regarding a submission which gave right answer on my compiler as well as ideone but wrong answer on codeforces
•  » » 5 years ago, # ^ |   0 Try to compile and run your solution with codeforces compiler: http://assets.codeforces.com/files/mingw-4.9.2.7z
•  » » » 5 years ago, # ^ |   0 Actually now we use mingw-tdm-gcc 5.1.0. For Windows users easiest way to install is to use PBOX http://pbox.me/ and install the package using the command pbox install mingw-tdm-gcc.
 » 5 years ago, # |   +8 As far as I can see this  printf("%I64d\n",n); is not necessary yet. I checked on cppreference.com using different compilers and here using GNU and MS compilers. This piece of code  scanf("%lli\n",&n); printf("%lli\n",n); works well. You can use %lld also. I'm not sure 100% that I properly tested it, but I think it is time to review this Q-A.
 » 2 months ago, # |   -10 Is it acceptable to use the blog to ask for help when stuck on a problem? Provided that it's not the problem of an on-going contest and that i can show at least a reasonable attempt to solve the problem by myself. I did so in the past and i got some downvotes, i don't particularly care about contribution points but i would like to know if i should use some different channels for seeking help.