Hello everybody!

I am glad to announce that Codeforces Round #138 will be held today at 19:30 MSK. I (Vasiliy Vadimov) am the author of this round. It is my first Codeforces round, I just helped other authors to prepare their rounds before.

I would like to thank Gerald Gerald Agapov for his help in the preparing of the round and Maria Delinur Belova for translation of the problems' statements in English. Also I am grateful to Mike MikeMirzayanov Mirzayanov for such an excellent contest system as Codeforces.

Good luck! I hope you will be interested in the problems.

The point distribution is standard in both divisions (500-1000-1500-2000-2500).

UPD. Attention! D language will not be available on this contest.

UPD2. The round is over, top-5 in both divisions:

Div1:

Div2:

Congratulations to the winners!

Also I am apologising for mistakes in statement of problem div1 A/div2 C. The tutorial will be published tomorrow.

UPD3. The tutorial is available here.

Good luck and having fun to all!!! I hope, that problemset will be interesting.

http://nagradite.bg/vote/HekpoMaH-47464.html

Кстати, уж простите за оффтоп. Меня вот интересует вопрос целесообразности этого:

А как много пользователей не нажимают на "здесь", чтобы посмотреть, что же там всё же заминусовано? =) Может, стоит просто засветлять сообщение? Единственная причина, по которой мне может видеться полезным такой подход, -- огромные картинки и/или стены мусорного текста, но тогда хорошо бы сделать ссылочку, чтобы прятать их обратно.

На хабре, к слову, это сделано гораздо юзабельнее, лично по мне. Блеклость текста не мешает его читаемости, в отличие от полного его скрытия.

а зачем вообще затемнять коммент?

Чтоб знать, что минусовать.

Когда ветки огромные или over9000 сообщений я читаю либо комменты с "+20", либо скрытые.

Иногда нажимаю, иногда нет. Вообще, нравится эта штука со скрытием. Не понимаю, в чём проблема.

Waiting for interesting and useful Contest.

What do you mean by "D language will not be available on this contest". Is there no translation of the problem D?

No This mean the D programming language is not available

No, it means that you cannot submit solutions written in D programming language. See http://en.wikipedia.org/wiki/D_(programming_language)

about problem C:

what is the answer of ((()))? should be 0

or 0 ((()))

?

I think any of them would be ok.

So you can print any proper subsequence, including empty. Anyway, do not ask questions about problems during the contest here, for this purpose there is "Questions about problems".

Not important, hidden.

I asked about this. They said: "Not important".

Problem E was great.

I can't comment on E as I had not even read it during the contest, but I actually liked problems

My first hack in Division 1 :)

`[[]`

:DThanks for telling the testcase you hacked me with :D

Can anybody teach me how to solve div2 E? Lucas?

You can calculate how many ai is in aj. So you can find the formula is C（k-1+j-i，j-i） （It is combination number）. And you can use C(a+b+1,b+1)=C(a+b,b)*(a+b+1)/(b+1) to get C.

D and E are too hard hah....sad....

Hi friends, I get WA on Test Case 23 and I dont understand what happend. Thanks in advance.

Under "Answer" is the correct answer for the test. Under "Output" is your output. You have no output for that test.

Edit: lol, don't edit your post like that :)

Thanks friend, Now I see this problem.

Div 2, D problem. in test where's |t|>|s| which answer must be?

No, because there is no substrings at all. So no symbol (and there is at least one) is covered.

thanks a lot!

The correct output is No. You can't make the substring. I failed on test 115 that was aa aaa , silly mistake

I failed on the same test, silly mistake.

I spent all the time in the first three problem so that I didn't read the problem D,E.I think they are good problems,thank you!

Our ratings have changed 2 times! Admin please fix this error!

UPD: I think it's fixed already, thanks :)Admin, please, dont fix it ;)

Yes, I am DIV 1 now... This must be a mistake (+180 pts) ...

Div 2, problem B. Where is my mistake? id: 2192405.

Convenient to click 2192405

Try this input:

The output should be

`3 5`

, but yours was`1 5`

.Thanks a lot.

tt。。。i got the same wrong test ,there are some same number appear later

Can someone please help me with problem C div 2, I got WA on test 58 and I can't find my bug. link: Link

Perhaps you are pop()ping too many elements when kt.size()==0? Here's a smaller failing test case:

`[[[]]])`

Nice problems — I liked the contest very much! Probably a bit on the hard end, but still :)

Thanks for your great contest! The problems were really good and enjoyable. But I have a question: after the contest my rating became 1557 and about 10 minutes later it became 1503! And now it's again 1557. What happend? What was the problem?

http://codeforces.com/contest/223/submission/2199884 Can someone explain please?

Actually, you output a symbol with code 0 before the string, at least on my system.

It will be better if someone give detail explanation of problem D and E. Please someone help ...

On div2 C i did so: Found every correct sequence and counted the maximum of ['s a correct sequence have and then saved that sequence. But i got WA on Pretest #9. Maybe i did something wrong in the code, or i don't know, but i find my solution to be ok.

First of all, it would help to write your submission number 2203267 if you want to get any help. Secondly, if you have looked at it yourself, which you should have done, then you would see that on test 9 your output is:

which has 5 [] braces, and the checker tells you exactly that.

Finally, in the following case:

The number of correct non-empty sequences is 1,250,025,000 which is a lot, so I assume that your solution would get TLE even if it's corrected.

Well, i don't think so. My solution has a time complexity of O(N), using a stack. In O(N) time, on a vector, it puts 1 on the ith position if that position is from a correct bracket sequence. After that, also in O(N) time, i search for the correct sequence which has the most '['s.

Also, I asked for help because the 9th test is too long (I can't copy the test to see what's wrong, because there is "..." at the end.).

Thanks for the answer also, even if it is not the one that I wanted.

Sorry to interrupt, but why the tutorial link leads to a "ru" page?

Because there is no english editorial yet. UPD. Sorry, there it is :)

Could anyone translate the tutorial? I don't understand Russian, google translate sucks and i want know the solutions...

You can change the "ru" into "com", or follow this:http://codeforces.com/blog/entry/5301

I am having wrong answer in Test 78. The test case is too big and thus got truncated. I have been trying to find the bug for a while now, could someone help? Here's my code.

Your solution produces wrong answer on this test:

Unfortunately, I copied the wrong code. Now it's corrected. Could you please check?