MikeMirzayanov's blog

By MikeMirzayanov, 7 years ago, translation, In English,

You may read complete rules here.

The text contains only preliminary rules of Codeforces contests — something surely will change. In particular, I hope to help the community to find the illogic in the rules. However, I have already discussed the format with programming contests dinosaurs and made unrated alpha contests — it seems rules are OK.

I think than the format 5 tasks x 2 hour is quite good. For this reason, in the near future we will not change it, but of course, experiments are possible.

1. Before the competition all participants are divided into rooms, each room contains about 20 participants. For now random strategy works, but after a while it will be somehow correlated with the rating.

2. The start of contest looks quite like ICPC: all problems immediately available for viewing/solving, the statements are simple and understandable. Choose the problem and begin to solve it. I think the idea to order problems by difficulty is good. The aim of the participant is to earn as much scores as possible.

3. The cost of the problem can be determined by the following table. For example, if the problem B was solved after 10 minutes of contest, then it costs 1000 — 4 * 10 = 960 points. For each attempt there is penalty of 50 points. So, if the problem B was solved after 10 minutes from the beginning with the third attempt, the score for it is 1000 — 4 * 10 — 2 * 50 = 860 points. However, no matter how much attempts you did and when you solved the problem, the cost of the solution can not drop below 30% of points (see the column "Min. Score (30 %)").

Problem

Max. score

Min. score (30%)

Loss (points per minute)

Score at the contest end

A<o:p></o:p>

500<o:p></o:p>

150

2 points

260

B<o:p></o:p>

1000<o:p></o:p>

300<o:p></o:p>

points

520

С

1500

450

6 points

780

D<o:p></o:p>

2000<o:p></o:p>

600<o:p></o:p>

points

1040

E

2500

750

10 points

1300 

4. And now comes the time when you solved the problem and submitted it. It will be checked only on preliminary testset (also we call such tests "pretests"). It is known that pretests do not check solution completely. Usually there are 2-10 pretests, and the fact that the solution passed pretests says only that it is quite reasonable. Typically pretests not contain the maximal tests, corner cases, etc.

5. Once your solution passed all the pretests, you'll get points for solved problem (see formula I described above). Also you now have an alternative — that is, if you are confident in the correctness of your solution, then you may want to lock this problem for yourself. If you have locked the problem, you will not be able to resubmit it under any circumstances. On the other hand you'll get the interesting possibility of hacking other participant's solution of participants from your room.

6. If during the contest, you have solved the problem, then it is locked, you can view and try to hack solutions of participants from your room. In the process of hacking, you can offer a test (or a generator program which outputs it to the standard output) on which hacking solution will not work correctly. If your test really breaks hacking solution, then it will become "Hacked" and its author will lose scores for it. Also he/she will receive announcement about successful hacking attempt and if the problem was not locked by him/her, author may fix the solution and resubmit it. But while resubmitting the solution will be judged not only on pretests, but on the hacking test(s) too. The hacking tests are unknown to the victim.

7. The target for any hacking attempt is the last currently accepted solution for this problem.

8. You may resubmit the solution at any moment, but it may reduce your score. It happens if resubmission is successful (i.e. passes all the pretests + previous hacking attempts). In this case, the previous successful attempt would be considered as a reason for penalty (see item 3).

9. After a successful hacking attempt you'll get 100 points.

10. After unsuccessful hacking attempt you'll lose 50 points.

11. If you have locked a problem, but your solution has been hacked, then you can still hack other participant's solutions.

12. Hacking attempt should contain a manual test or a test generation program (generator). Generator is a program which outputs the test to the standard output. The generator should always give the same test, for example, you can not initialize the random using the current time, etc. In any case, you have to follow very closely the format of the test. Each line should end with a newline.

13. Hacking attempt can be ignored. This happens in several cases: the test is invalid, generator fails, victim resubmitted the problem while hacking, concurrent hacking attempt was successful.

14. Of course, during the competition it is forbidden to communicate with other participants, share ideas, solutions or hacks. In general, violation of the rules of sports and personal ethics can lead to disqualification. It is prohibited to access the network, attack system security, work with filesystem, try to hack the judge and etc. In short, respect yourself and others.

15. Solutions and test generators can only use source code completely written by you, with the following two exceptions:

  • 1) the code was written and published/distributed before the start of the round,
  • 2) the code is generated using tools that were written and published/distributed before the start of the round.

Any usage of third-party code should not violate the right holder’s license or copyright. Remember that published code is not always free to use! At the request of the right holder, any code that violates the license or copyright may be considered as violating the rules.

All the changes in the code from exceptions 1) and/or 2) must be made solely by you. If there are any doubts about the time of publication, possible collaboration etc., a participant will have to prove his/her complete innocence by presenting compelling and satisfactory evidence.

Currently, the only reliable proof is the presence of code on the Internet and the presence of the used edition in the cache of well-known search engines.

For example, this rule accepts the use of the code from the website http://e-maxx.ru/ if the code was written and published/distributed before the start of the round. With the help of search engine caches, it can be easily shown that such code doesn't violate the rules. Similarly, it is permissible to use the code from a book/article that was published before the contest. On the other hand, using team reference code (for example, prepared for ACM-ICPC World Finals) is not allowed if there is no reliable and objective way to prove that the code was written before the contest.

This rule doesn't loosen the rules about prohibiting of communication, discussion, or any other form of communication between the contestants on any topics about the problems during the round.

16. Solution code obfuscation and creation of obstacles to reading and understanding the solution is prohibited. It is forbidden to use any special techniques designed to complicate the reading of the code, to understand its workflow.

17. After two hours of entertainment contest ends. For each participant we choose the latter solution for each problem (of course, only successful). All such solutions are rejudged on the final set of tests. As a result, some solutions fail. The final result for the competition is the sum of scores for all the solutions that have passed final testing, plus the scores that you have received (or, conversely, lost) while hacking.

All, finita la comedia, that is, game over.

Waiting for your opinions,
MikeMirzayanov

P.S. I avoid term "challenge" deliberately. It can't be translated into Russian well, also Topcoder may have ambitions for the exclusive "Challenge phase", etc. I ask you to use term "hack" in discussions and comments. Thank you for your understanding.

 
 
 
 
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7 years ago, # |
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Are you going to introduce these rules in beta round 19 or make another unrated round for greater number of people?
  • 7 years ago, # ^ |
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    The second. It will be Codeforces Alpha Round #21 (Codeforces format)
    • 7 years ago, # ^ |
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      will Codeforces Alpha Round #21 be rated?
    • 7 years ago, # ^ |
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      one question, If one's solution is hacked(but not by us), can we still see the code but we are not given permission to hack or we can't see the code and there is no permission to hack?
      • 7 years ago, # ^ |
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        Probably you may not see someone's solution if it's already hacked.
        It'll be so until that someone submit a new solution (if the problem wasn't closed; if closed - NO WAI), that again passes pretests And tests, that used to hack this person's solution before.
7 years ago, # |
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I think that these rules seem interesting, we should see in practice how they works :)
7 years ago, # |
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I think it would be good if there were an additionally, say, 20 minutes of hacking after the first two hours have passed. No further submissions could be made during this time, only hacking. But then again, perhaps the two hours are enough. I can't wait to try this. :)
7 years ago, # |
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This contest style looks pretty cool. I don't think extra time is necessary for hacking after the contest. In Division I contests for me at least, I usually do 3 problems or so, and then don't know how to do the others :P So I'll have time to hack :D
7 years ago, # |
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I don't think hacking is an effective way to get scores with this rule. (It decreases the time to solve problems, and we can't resubmit if we try to hack.) I think it will work fine if there is no penalty for unsuccessful hacking.
  • 7 years ago, # ^ |
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    But if there is no penalty for unsuccessful hacking, then people might start making hacks recklessly without analyzing the solutions.
    • 6 years ago, # ^ |
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      Would that really be a bad thing?

       If BF/load are issues just add an X seconds delay between hacking attempts.

      I don't really think it would be useful to try "hacking" at all. In TC challenges were already too much of an unusable gimmick for most div1 coders.  But if besides of the risk of losing points, you also add that you cannot resubmit any more and that you have to use time during coding phase it is too much.
      • 6 years ago, # ^ |
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        I really prefer it in the normal ICPC format than adding the hack stuff. As you said, challenging in TopCoder is useless for me in div1.
  • 7 years ago, # ^ |
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    Sometimes too few time left and you know that it's not enough for solving one more problem. It'f perfect moment to start hacking).
    One more argument for making penalty for unsuccessful hacking - it should stop hacking flood and brute force hacking :-D
7 years ago, # |
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Why revealing that a solution has been hacked at all?

Just give the outcome result to the hacker and add or subtract the points, but don't reveal anything else.

That has been proposed in TopCoder forums long ago but I can't find it anymore. 

I think that this it is even better opportunity to use these rules considering that hacking and coding phases are not disjoint here.

I find it somewhat unfair to you get the info that your solution is flawed and you get to resubmit it, but I don't get it just because someone hacked yours. This rule would prevent this.

Also, you can't submit something that doesn't work at all so that the whole room would feast on it. The submission must pass this basic test set so I wouldn't mind if two people find the same bug and both get points for it.

Please consider the idea. I really think it would fit here.

Luka
  • 7 years ago, # ^ |
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    With current rules there is an important trade-off: you either try to hack solutions (but then the points for problems that you haven't submitted yet are decreasing) or solve other problems (but then you risk missing a lot of points for hacking). With what you suggest the second problem becomes much less critical, if not disappears at all.
    • 7 years ago, # ^ |
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      Sure.

      I just think that for me as a contestant it would be much better if I didn't have to depend on other peoples strategies and luck. I can devote as much time as I like to coding and spend the rest hacking.

      Everybody choose their own strategies but it doesn't effect others. This way luck factor is greatly reduced to the room assignment. The order I check others solution doesn't matter and the time I start checking others solution doesn't matter. Only my hacking skill and the strategy I choose matters.

      While I understand your point, I disagree that having this trade-off around is valuable. It might be fun in the beginning, but I think it would be chaotic - the rush to be the first to hack would be annoying and in the end I think that luck would play a significant role to the success of chosen strategy. 

      Keeping track of the scoreboard all the time would be pretty distracting for problem solving that is still (I think) the most important part of algorithmic contests.

      Well, maybe I'm wrong :)
      • 7 years ago, # ^ |
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        Have you participated in Alpha Round #20? It was very fun! :)
        IMHO, with your system the whole idea of combining the coding and the hacking phases together almost doesn't make sense. I agree that the importance of hacking is now emphasized, but well, that's the feature of the format. By the way, in alpha round #20 ivan.popelyshev started to hack solutions only after he submitted all 3 problems himself, and still made it to the 1st place.

        As for the tracking of the scoreboard — I'm sure there will be improvements of the interface that will make this easier.
  • 5 years ago, # ^ |
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    I like the idea that contestant with hacked solution have no info about it and more than one room contestants could gain points for hacking such solution.
7 years ago, # |
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What happens if I am 'confident' that I can not solve a problem in the given time. Can I lock that problem without submitting a solution and hack others solution for that problem?

I liked the idea of silent and multiple hacking by Kalinov. It makes sense.
  • 7 years ago, # ^ |
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    No, you can't lock a problem without submiting a solution. You can lock the problem and hack other solutions only if you solution passed all pretests.
7 years ago, # |
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I have a few questions about the new format:

1. The way I understand it, we cannot hack at problems we haven't submitted and locked ourselves. But we might have formulated usable test cases, even if we failed to submit. Would it be possible to lock a problem we haven't submitted - in effect we forfeit our chance to submit the problem any more in the contest - and then challenge?

2. In TopCoder, the text of solution code is unobtainable by copy-paste or any other way. This is essential to prevent automated challenges. Is there a similar restriction in the new format?

On the whole, this new format looks promising. Looking forward to the first rated match.
  • 7 years ago, # ^ |
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    2. In TopCoder, the text of solution code is unobtainable by copy-paste or any other way. This is essential to prevent automated challenges. Is there a similar restriction in the new format?
    No, you can't copy-paste other's solution.
    • 7 years ago, # ^ |
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      You can copy-paste other solution. It was proved by me.
      • 7 years ago, # ^ |
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        Here by Russian http://codeforces.ru/blog/entry/468#comment-6868
        • 7 years ago, # ^ |
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          It's a bug, the question was about rules.
          • 7 years ago, # ^ |
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            It's look like that authors tried to protect code by using flash.
7 years ago, # |
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Few more questions about the new format:

1- Rules talk about obfuscation, but is there any restriction similar to TopCoder's unused code rule? I have many defines for input reading in my Codeforces source template. They aren't meant to make it hard to read the code, but most of them are not used in a single problem, so there is a lot of unused code. For the CodeJam I added a comment at the beginning explaining the source file structure and where to find the problem solution related code.

An example of the defines are
#define InInt(N) int N; scanf("%d", &N)
#define InVectorInt(X, N) vector<int> X(N); for ( int i = 0; i < N; ++i ) scanf("%d", &X[i])

The input section of the main method may look something like
...
InInt1(N);
InVectorInt(points, N);
...

2- It has been stated that you can't hack without successfully passing the pretests, but how about making a solution that one knows passes many cases but not all. Submitting it, and adding small hacks to it until it passes the pretest and locking it. Then I start to hack others, what happens if my code gets hacked? Can I still hack others? Is it considered fair to have such an approach to be able to get hack points even if I can't solve the real problem? Rules says that worst cases aren't tested by the pretests, so maybe I can make a brute force, or maybe an O(N^3) solution when N <= 500, knowing that worst case won't pass but maybe pretests are small enough. If this isn't considered ethical enough (rule #14) it would be hard to determine if it isn't an honest mistake, so maybe allowing to lock a problem without passing pretests is the only way to really disallow this.
  • 7 years ago, # ^ |
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    what happens if my code gets hacked? Can I still hack others?
    You can still hack others
7 years ago, # |
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There seems to be a week point in the in-time-of-contest hacking. If someone with a fake ID (or lets say two friends) are in the same room, he may submit for N times (for an arbitrarily large amount of N) using his fake ID, and hack his solution with th original ID. This way, he gets 100*N points for free (which worths a lot for an arbitrarily large amount of N) :D
P.S. I can see that this way you will be mention his cheating and will disqualify him, but it's just a matter of canceling the potential of cheating as much as you can. Also, note that you won't even think of cheating if the process is done for a small value of N.

Solution: Don't let someone hack another ones solution for more than once (or twice)
  • 6 years ago, # ^ |
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    Sorry for writing in Persian:
    بابا اینها عقلشون به این جاها نمی رسه
    فقط ما ایرانیها این چیزها به ذهنمون می رسه
  • 6 years ago, # ^ |
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    راضیم ازت، عالی بود!
  • 4 years ago, # ^ |
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    In your scenario, these friends have to:

    1. Submit S1 that passes pretests but not T1.

    2. Submit S2 that passes pretests+T1 but not T2.

    ...

    N. Submit SN that passes pretests+T1+...+T(N-1) but not TN.

    So, I think, for large Ns it is simpler to solve the problem E instead and getting more clean scores :)

6 years ago, # |
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round #26 is rated or not??
6 years ago, # |
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I think it will be great to creat a raiting table for each room, something like on TopCoder, very comfortable. And from this table to have possibility to open users source codes for each task and also problem's text.
hm?
6 years ago, # |
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Hey everyone I'm new to this website and I have a question about submitting my codes. I tried submitting a java type file and i kept getting an error. any tips on how one should go about submitting your code for a contest.
  • 6 years ago, # ^ |
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    What error?
    Here's a sample Java solution for problem A from beta round #1
  • 6 years ago, # ^ |
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    You can check other solutions. Some steps:
    1. Proceed to the "Contests" page. (link)
    2. Enter one of the previous contests. (example)
    3. Proceed to the "status" page (status)
    4. Find some accepted solutions in Java
    5. Look at the code clicking the solution ID link.

    P.S. It seems to be that you just print the answers for the sample tests. Instead you should read the input data from the standard input stream.
    • 6 years ago, # ^ |
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      Thanks. Reading in the data was my problem. Appreciate your help.
6 years ago, # |
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Is it no more possible for DIV1 contestants to take part in contest only for DIV2 and be out of competition?
6 years ago, # |
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while I see the benefits to this approach, I never liked the whole hacking thing.  TopCoder does it and has been doing it for a long time, so fine, let it be.  I did like the original CodeForces judging way, such as used in the first 5 contests and onwards.  Having said that, I am not entirely opposed to the new way.  I haven't tried the new rules yet, so it will be interesting to see how it feels.
6 years ago, # |
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Can I do a request? Plz Plz don't forget the ICPC formet. Have some contests on that format also plz.
6 years ago, # |
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Can you resubmit your code after locking your code or your code be hacked by others?
  • 6 years ago, # ^ |
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    If you lock your code you can't resabmit it. In any other situation you can do it, but the score on this problem wiil be less, becose of time between submitions and 50-points penalty.
6 years ago, # |
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What about the following idea: after the finish of each contest, problemsetters upload all tests to all their problems as an archive (to some site). It's not difficult for authors to take an archive from the system ('Polygon') where the problems are created.

I don't know when the feature of viewing test data will be available on Codeforces, so I suppose this is the best solution. It's really not a good idea to ask tests in comments on the site, IMHO.

6 years ago, # |
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On the 32nd round I noticed div1 contestants couldn't hack others' solutions. Is it going to be like that in div2 only?
6 years ago, # |
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Will out of competition user's rating change after the contest??
6 years ago, # |
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I think codeforces can add a function that contestants can view others' codes after the contests in his/her room.
During the contest, I may not find a program's bug. When it failed system tests, I want to see it again ..
6 years ago, # |
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I was looking for these rules on the site without much luck - the link is provided in the email, can it be visible somewhere on the Home or Contest pages? I see now that the link can be found under 'Recent Actions' but, at least for me, it is not really a place I would go to when looking for the rules.
6 years ago, # |
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can u please allot div 2 members to seperate rooms and div 1 members to seperate rooms ?? like they do in topcoder ...
  • 6 years ago, # ^ |
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    In the case div 1 and div 2 are together - the div 2 contestants' wrong solutions will be hacked earlier and they'll get an opportunity to resubmit a correct solution.
6 years ago, # |
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@MikeMirzayanov: Any particular reason why successful hacks are not added to the global system tests?

I am asking because some hacks may expose bugs that the system tests may not cover.  In such a situation, a solution may get accepted because the author of the hack failed to check the solution or was in a different room.
6 years ago, # |
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Please fix "loose" to "lose". :)
6 years ago, # |
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Heyi.. how to register for contests? i am new to this site. and i didnt find any link which refers to "Registration for Contests".. i am little bit confused. am i eligible for contests or not? please give me an answer quick , so that i can register quick if i am eligible... 
  • 6 years ago, # ^ |
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    registration will be available here after 7:00am (msk)
    • 6 years ago, # ^ |
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      whats the time in GMT format?
      • 6 years ago, # ^ |
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        Time of registration shows here (in last column).
      • 6 years ago, # ^ |
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        Sorry, I forgot about other timezones.
        As Dembel say, you can see, when registration start on contest page. Registration to next contest starts in 12 hours before contest
    • 6 years ago, # ^ |
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      7:00 am will be after about 9 hours :)
5 years ago, # |
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Hi, im new here.. I am just wondering .. what if i don't submit a prob ? Will that reduce my results? (Please don't mind if my English is not so good..)   ^_^
  • 5 years ago, # ^ |
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    Your rating changes if and only if you submit a solution. You may carelessly register and watch prob. statements (you can do it even logged out) without worrying about rating. :)
5 years ago, # |
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I have noticed I cannot cancel my registration to a contest anymore. If I'm not mistaken, now the rules are that if you send a solution you will be rated.

UPD: Ok now I'm sure about it. It's a pity I cannot partecipate in this round... waiting for next week :)
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5 years ago, # |
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How a contest point include to CodeForces rating point ??
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    5 years ago, # ^ |
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    Only the rank is important. Points as numbers don't mean anything.

    Exact formula is not public.
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5 years ago, # |
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I have a suggestion. 
Maybe... we can get different scores after hacking different problems.
i.e. for problem X, if its max. score is S, we can get S * 10%  points after a successful hacking attempt, or lose S * 5% points after unsuccessful hacking attempt. 
Er, just a personal thought,^_^...
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    5 years ago, # ^ |
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    It is not a good idea, I think. The difficulty of a problem is not relevant to the hacking difficulty. Sometimes it is easier to hack harder problem since there is a good chance for someone to have buggy implementation or wrong algorithm on it. On the other hand, sometimes tricky easy problem gives more opportunity for successful challenges.
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5 years ago, # |
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Can I see the test case that was used to hack my solution after the contest?
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    5 years ago, # ^ |
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    Yes. Goto "hacks" page in contest.
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5 years ago, # |
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How can I see the whole input in Source view? i.e. Test #6

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4 years ago, # |
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So many experts are here,I'd like to raise my quesiton:I wonder how can I get a shirt if possible ? Thanks beforehand.

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4 years ago, # |
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I have a doubt . If I solve the first problem 10 minutes after the start of competition and second problem after further 15 minutes i.e. 25 minutes after the start of competition . Then while calculating the score for the second problem solved will the time considered bye 25 minutes or 15 minutes . If it is 25 minutes , then is it not better to solve difficult problems first because there the penalty is larger . The text says it is better to solve problems by order in difficulty ( ascending or descending ) . May be difficult problem will large time so will affect time of larger number of problems , hence ascending order of difficulty . But just clarify which time will be considered . Thanks .

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    3 years ago, # ^ |
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    Ofcourse 25. Otherwise, one would submit the solutions all at once. Even after 115 minutes, this way would give 30 % of 500 to one problem and full score to remaining problems.

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2 years ago, # |
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Please even once vote up my comment ! I'd be happy.

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    2 years ago, # ^ |
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    There.

    Too bad I'll downvote repeated versions of this post and any other offtopic/spam comments, so you'll, in fact, lose contribution due to trying too hard...

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

    Sorry, my screen was upside down
    Voted down by mistake....
    You cant expect people to upvote you for that comment...

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

.

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21 month(s) ago, # |
Rev. 2   Vote: I like it +5 Vote: I do not like it

Why no format requirement? I posted code like ~~~~~ printf ("%d ", a[i]) (i meant several spaces but it only display one and i dont know y) ~~~~~ and succeed.

Besides, where I make private special judge(That means no fixed answer) (Another website is also alright)

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

Hi I am quite new to Codeforces.

I am have a couple of questions:

a) If I have locked my solution, and someone hacks my solution(as it happened today), then can I unlock my question to resubmit it? Also will I be receiving any points for a submission that passed the system pretests but got hacked later. As I see, it is showing '-1' in the points table against that question.

b) Also, how to hack anyone's solution. How to create a hack? Etc.

By the way, can anyone tell me what is this Virtual round? DO I get ratings for participating in Virtual rounds?

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

Can I use third party algorithm or data structures? Not other participants code on the contest. And can I use other participants codes from previous contests? Writing DFS from scratch is so difficult. -Edit. Sorry I missed clause 15.

  1. Solutions and test generators can only use source code completely written by you, with the following two exceptions:

1) the code was written and published/distributed before the start of the round, 2) the code is generated using tools that were written and published/distributed before the start of the round.

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

    But now I have another question. Is there any compile-time limit? If an open source third party algorithm library is big, can I copy and paste whole library into my Source.cs file?

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

      As far as I remember, compilation time limit was 10 or 15 sec but I think you'll hit source limit first

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

        Thanks. I checked myself that maximum source character is 65535.

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

Whom to contact for errors in system testing ?

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

Maybe I'm really slow, but I haven't found the unambiguous answer to whether we are allowed to use our own pre-written code?

the code was written and published/distributed before the start of the round

I guess it implies that I can implement all the classical algorithms myself (instead of writing it from scratch every time or unethically copy-pasting from public sources) and publish it on GitHub or other hosts.

Could anyone please confirm?

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

Let a solution contain uninitialized variables. It may or may not return wrong answer during pretests. I tried to hack such a solution, but got unsuccessful hacking attempt. Is there a way by which we can hack these solutions surely. (Not on chance!)

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

    No

    Read about undefined behaviour :)

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

    For Educational Rounds, you can download the exact version of compiler used and test locally (you will need Windows for that). An alternative is to use custom invocation tab. I don't think there is any good way to challenge them in the normal rounds though.

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

hello guys, i'm quite new to codeforces. I have a problem that whenever i try to submit my c++ file it gets stuck and doesn't move to the next page, but if i try someone else's code it run perfectly. I have checked my code on codeblocks and it seems to be giving the right answer as the testcases say. Am i doing something wrong??