MikeMirzayanov's blog

By MikeMirzayanov, history, 22 months ago, translation, In English,

Hi everybody!

First, I invite you to take part in an official Testing Round #12. The fact is, the Codeforces team has made numerous changes to the platform (details are below), and we want to be sure that the basic functionality remained unchanged. This round will have a shortened duration of 1.5 hours, consist of 3 (maybe 4) problems that you might have already seen before. Its purpose is to test the system on the one hand, and on the other hand — to brighten up a Wednesday evening. Of course, the round will be unrated.

Now the main thing. This coming Friday (yes, the 13th of November) Codeforces starts another line of rounds. We called them Educational Rounds. Using my students at the Saratov State University Programmings Competitions Training Center as an example, I regularly notice that even those who have a considerable progress in the results on the rounds often have narrow purview in terms of standard topics and ideas, they are not familiar with many well-known problems and methods. The fact is, the rounds often avoid any folk or classical subjects, thus underdeveloping the purview of young generation of the participants.

We are pleased to announce the start of a series of educational rounds! They will take place with the regularity of a round 2-4 times per month.

Their characteristics are like that:

  • The duration is classic — 1.5 — 2.5 hours;
  • The goal is rather to practice and to educate, than to compete;
  • Not only problems, but also exercises can be used;
  • Useful, even well-known ideas will be reused in order to introduce them to a wide range of participants;
  • Often the formal text of the statements;
  • Unrated (perhaps for now);
  • We will try to conduct them in the ACM-ICPC mode (if there are long waiting lists, we may change the approach);
  • The results that are obtained after the end of the round, are preliminary;
  • After the end of the round will be a 24-hour period of open hacks — any visitor of Codeforces may try to hack any complete solution to a problem of the last round (either from a contest, or from practice), the source code of hacking solution is available (you can copy the text and, for example, stress it);
  • All successful hacks from the previous item will be added to the official test set and after as long as 24 hours after the end of the round retesting of all complete solutions will be made;
  • Only after the final standings based on improved test data, the results are final;
  • The results of a round are calculated separately by division;
  • Our ability to process such problems are limited, so actually the test suites from the jury are expected to end up incomplete — we are looking forward to your hacks!

Basically, we will be oriented towards the members of the second division, but often these rounds will be of interest to more experienced participants.

For now preparing problems to these rounds will be concentrated at the Saratov State University Programming Competitions Training Center, most of the work with the problems will be accomplished by Edvard homo_sapiens Davtyan. We wish him good luck, enthusiasm and energy!

See you at the Testing Round #12, and later at the Educational Codeforces Round 1.

 
 
 
 
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22 months ago, # |
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excited! it may be Educational Hackforces Round 1, very very interesting.

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22 months ago, # |
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Since I'm going to hold a codeforces mashups for my students this Saturday, I wonder whether Gym/Mashups will work normally during the 24-hour period of open hacks. Thank you.

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22 months ago, # |
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No rating change for a while then :( Keep it up tho!

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22 months ago, # |
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This is an excellent idea! It will fill gap between classical books like CLRS and problems on rated contests.

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22 months ago, # |
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how much time does a 5*1000000000 loop take on codeforces?

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    22 months ago, # ^ |
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    Not the right place for a question like that.

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22 months ago, # |
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Dose the Educational Codeforces Rounds have a different styles in It's tutorials or the as same as the regular ones MikeMirzayanov ?

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22 months ago, # |
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I am very looking forward to the coming contest ! :-)

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22 months ago, # |
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The Educational Rounds seems a great idea. I suggest introducing a separate rating for the Educational rounds, this will act as an incentive for contestants to participate more actively in them..

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    22 months ago, # ^ |
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    I think, everyone, who really wants to increase their knowledge will take a part in educational rounds without any additional points. People, who write contests here only to make their rating higher are not welcome (by me). In my honest opinion.

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22 months ago, # |
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How will the Educational Codeforces Round be beneficial to the Div 2 participants ? what are the differences between Div 2 and Education Codeforces Round ?

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22 months ago, # |
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I think I'm gonna love Codeforces more and more ! Gooood Job !

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22 months ago, # |
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thanks for this opportunity codeforces :p

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22 months ago, # |
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Interesting :D

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22 months ago, # |
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Great , just i wish u make it rated (Educational rounds)

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22 months ago, # |
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This is great! Most of my knowledge in algorithm/competitive programming comes from CodeForces, and it's great, but I sometimes don't know super basic stuff... (For example, at some point, I think I had way more experience in segment tree than dynamic programming... xD.)

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22 months ago, # |
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(unrated) excited !! :D great thinking mike ! :)

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22 months ago, # |
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Thumbs up if you learned the word "purview" from this post :)

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    22 months ago, # ^ |
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    I was too lazy to read the whole post, so I learned it from you. :D

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    4 months ago, # ^ |
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    Read the russian version of this post, learned the word from you (:

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22 months ago, # |
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Thank you Codeforces team :) It's a great idea.That's why Codeforces is always one step ahead than other contest sites :) But i think separate rating system for the educational round should be introduced.It will surely increase the number of participants!

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22 months ago, # |
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Thank you very much.

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22 months ago, # |
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It is Very Good Idea :) But Please & Please... Good Translation :D Thanks

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22 months ago, # |
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It is a very great idea. I often notice that my skills are honed into participation in Codeforces and Topcoder contests. That does not really mean that I am good at algorithms. While speaking with guys who specialize in knowing theory behind various algorithms, I often come to conclusion that my knowledge is very limited.

Another side is the fact that my skills are not very useful at production. While at contests I often use hashing or treaps, it is a horrible idea to use them behind real-time system, given there are better alternatives. I suggest making these educational rounds in such a way, that encourages contestants to use different approaches to the same problems. For example, you can make three different tasks: "Strstr Hashing", "Strstr KMP", "Strstr BM". Then add a line into statement: "This problem should be solved by using KMP algorithm. While you can technically solve it using different algorithm, the purpose of this round is education, and cheating negates your educational progress". I suppose that will work as well as our "Virtual participation" function, and it will only work if the round is unrated.

I am looking forward for participating in these rounds.

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    22 months ago, # ^ |
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    I suggest making these educational rounds in such a way, that encourages contestants to use different approaches to the same problems. For example, you can make three different tasks: "Strstr Hashing", "Strstr KMP", "Strstr BM". Then add a line into statement: "This problem should be solved by using KMP algorithm. While you can technically solve it using different algorithm, the purpose of this round is education, and cheating negates your educational progress".

    The trick "let's think about one problem in different ways" is quite useful because sometimes it gives notable time savings in explanations, sometimes it makes this explanations spectacular — all in case when problem is easy enough, and mb in some other cases. But noone should use it as a reason to memorize the implementations of three different algorithms to get AC . It's the only possible reaction to "should be solved by KMP" for most part of users, I know it by my own observations during last years (and personal experience, of course).

    The idea that "the problem should require competence NAME to be useful in learning process" is not bad by itself, especially because the only one well-known and undeniable method of learning to code specific algorithm in contest is actually doing it. But it is also known that problem must show the importance of algorithm (or it's basic ideas) and related topics of math and physics in natural or at least non-artificial way [Arnold] .

    This words may seem senseless and empty until you start to think what's the target of competitive programming instead of thinking about problems it poses in regular rounds)) Such thoughts made me to write a small blogpost about CF educational rounds, but it's not yet ready to be posted.

    Let's say more about what is called "natural way". It's ok when you define determinant by 3x3 case as "oriented geometric volume created by three 3d vectors" because there is no way to invent determinant from scratch and it's possible to understand what's the motivation of volume sign, what's the meaning of value and how parallelepiped looks. But you shouldn't define DFS as "this recursive function that can be simply coded to traverse given graph", first of all you should say about several important problems that can be represented as problems about graph structure, you should show how this graps looks and how those problems becomes amazingly simpler when you classify edges by DFS traversal strategy [Sedgewick] .

    Let's continue about "natural" learning of STRSTR. As for me — the only more or less "ok" way today is to learn string algorithms from [Gusfield] and several other sources during long evenings of this cold winter. It's terribly difficult from time to time or even impossible in case you are not ready for such difficulty level or for such "type of activity". I don't know about any simple and purely creatively-technical option to learn STRSTR algorithms in natural way. The question "how to train contestants with sensibly less effort from their side?" became simpler when I've started to think about automated system for this. But it produces many problems which I consider unsolvable with current techniques that online judges use, for example:

    • How to overcome "memorizing problem" mentioned above? The usage of "hashing + map/set" or "hashmap/hashset" can become mandatory in "STRSTR HASHING" with some modifications so the problem won't be solvable by memorizing classical implementation. But it's not a natural reason to learn hashing, efficient data structures, or string algorithms.
    • How to avoid phrase "solve it by METHOD_NAME"? You can set extra-small ML and anti-hash for "STRSTR KMP/BM" to disallow suffix automata and Rabin-Karp so you don't even need to add line "don't use them" in statement. But it's not a natural reason to learn KMP/BM and methods of effective memory usage.
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22 months ago, # |
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Great idea, the more CF rounds of any kind the happier I am.

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22 months ago, # |
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Will be there any pre-declared topics? If it is, then we will be able to learn them before the round and test our skill during the round. It would help us to learn those topics better. Another request as they are Educational round please make the editorial more details not only hints.:D

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22 months ago, # |
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Maybe you could add a rating for this Educational rounds, it would be more fun and competitive, so that every user has two ratings, Educational rating and Rounds rating???

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22 months ago, # |
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will we need to register for these rounds? if yes, how? if no, then can just anyone participate in these while they are in progress?

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22 months ago, # |
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It will be helpful for new programmer. Thanks.

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22 months ago, # |
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Is it on the same lines as Code Monk on HackerEarth?

Btw, I found codemonk really enjoyable with the problem that the difficulty curve of the problems was really too steep for an educational contest.

I hope you guys take care of it here at CF. Cheers! :)

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22 months ago, # |
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Codeforces is becoming the one stop destination for competitive coders (y) .

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22 months ago, # |
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No problems in the test contest.

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22 months ago, # |
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It would be nice to give problems :)

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22 months ago, # |
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I can't see any problems in the test round.

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22 months ago, # |
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cant see any problem?

Celebrate Diwali folks! Happy Diwali :D

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22 months ago, # |
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no problem

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22 months ago, # |
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Problems are not visible to me :(

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22 months ago, # |
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I cant see any problems!

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22 months ago, # |
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No problem statement. Am I the only one?

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    22 months ago, # ^ |
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    same here

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      22 months ago, # ^ |
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      I was doing my assignment -_- . I left it for "THIS" ?? really? -_- :3

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22 months ago, # |
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Are you kidding with us ?

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22 months ago, # |
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Are we being tested?

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22 months ago, # |
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I hope there will not be a 15 minutes delay.

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22 months ago, # |
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we have to guess the problems ?!

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22 months ago, # |
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Guys where the problems are? I can't see them. Only empty list. Issue only with me?

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22 months ago, # |
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Seems that I'm not alone...

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22 months ago, # |
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problems are hard enough to be invisible. :D

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22 months ago, # |
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Testing round : it tests our patience!

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22 months ago, # |
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we learnt that Testing round has no problem.

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22 months ago, # |
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where are the problems?

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    22 months ago, # ^ |
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    testing round is tests our patient :)

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22 months ago, # |
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Works fine, I'm happy

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22 months ago, # |
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the problems are very easy

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22 months ago, # |
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the tasks were too easy for us :))

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22 months ago, # |
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When you first see the contest with no problems :D

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22 months ago, # |
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it seems that the basic functionality didn't remain unchanged :D

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22 months ago, # |
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No Problem!!

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22 months ago, # |
  Vote: I like it +9 Vote: I do not like it

So the round is to test how the system behaves if there are no problems in an active contest.

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22 months ago, # |
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where the problems are?

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22 months ago, # |
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Yes, MikeMirzayanov and GlebsHP aren't online :D

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22 months ago, # |
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the problems level is too tough that they haven't even kept it in problem set

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22 months ago, # |
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Are u testing our patience? -_-

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22 months ago, # |
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Time is going on,but problem is waiting.

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22 months ago, # |
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Please, brighten up a Wednesday evening a little more :)

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22 months ago, # |
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I'm registered in the Testing Round but I can't see any problem (I mean problem statement for solving). Is there any? Is this normal?

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    22 months ago, # ^ |
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    Have you tried turning it off and on again?

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      22 months ago, # ^ |
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      Yes, several times, but it didn't work :(. I'll try formatting the laptop.

      Thanks for the advice!

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22 months ago, # |
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First time to solve all problems in a contest :D

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    22 months ago, # ^ |
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    First time there's noone ahead of me after 10 minutes.

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22 months ago, # |
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it seems that I have to study for tomorrow's exam instead of solving blank problems!!

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22 months ago, # |
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Just hack!!!

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22 months ago, # |
Rev. 2   Vote: I like it +3 Vote: I do not like it

the new round is too hard to see problem

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22 months ago, # |
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like you make your own destiny , you should make your own problems :v :D

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22 months ago, # |
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where is the problems in testing roung now?did i miss something?

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22 months ago, # |
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Maybe wrong contest time? :D

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22 months ago, # |
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Can you make this round rated? So everyone will be 1st and earn a lot of ratings.

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    22 months ago, # ^ |
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    If everyone is first then noone is first.

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      22 months ago, # ^ |
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      If everyone is first then noone is second.

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22 months ago, # |
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It seems that reading all those comments above is more fun than contest itself :)

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22 months ago, # |
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I want sleeping..........

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22 months ago, # |
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Wow!!! What a problem set....nice!!!

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22 months ago, # |
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I told my teammates(he came back just now) that in the new testing contest,if you solve a problem,it will disappear,and now I have solved all the problems!So you can't see them.→_→

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22 months ago, # |
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the problem is not the problem,

the problem is your attitude about the problem !

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22 months ago, # |
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I want say :6666666666

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22 months ago, # |
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I'm tired of waiting you lost one participant, good luck for others with contest

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22 months ago, # |
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after seen there isn't any problem :(

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22 months ago, # |
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Where are all the questions?

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22 months ago, # |
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Oh, come on guys, it's OK that there's no statements. This round is held to see if there would be any bugs or problems. Well, it seems, there they are :)

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22 months ago, # |
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+100 for successful hacking attempt of codeforces!

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22 months ago, # |
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Keep calm guys.. it's just an error :)

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22 months ago, # |
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please tell me where are the problems. Am I the only one who can not see the problems?

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    22 months ago, # ^ |
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    you're not alone

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      22 months ago, # ^ |
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      I set my mind at rest after I saw the comments... wow,the pictures above are so funny...

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22 months ago, # |
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Sorry, we need to move the round forward for 3 hours.

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22 months ago, # |
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Well, time to go sleep.

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22 months ago, # |
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Codeforces has finally grow up and it solves its problems itself :D

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22 months ago, # |
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Mike wrote right thing in the blog : "This round will have a shortened duration of 1.5 hours, consist of 3 (maybe 4) problems that you might have already seen before"

I saw this before:

First problem : No tasks

Second problem: No coordinator

Third problem : No basketball for me :)

It was a good test of our nerves...

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22 months ago, # |
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there we go, the contest starts 3 hours later :(

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22 months ago, # |
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is there any technical prblm ? I cant see any prblm on testing round ! -_-

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22 months ago, # |
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I solved E by intersection of half-planes!

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22 months ago, # |
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May be it is the longest delay ever in the history of codforces.

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22 months ago, # |
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this is a real sad story

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22 months ago, # |
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Am I getting Blind . I can't see any Problem ..... Ummm....

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22 months ago, # |
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we have not enough patience for 3 hours for waiting testing round.

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22 months ago, # |
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delay for 3 hours... I choose to die....

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22 months ago, # |
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Thanks to 3 hours delay, I can now register for the contest. Am I the only one happy about the delay? :D

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22 months ago, # |
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Why postponed?

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

Are there enough jokes about testing our patient in comments or I can add another one?

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22 months ago, # |
  Vote: I like it +51 Vote: I do not like it

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22 months ago, # |
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So many hacks today!

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22 months ago, # |
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Educational rounds, I understand, but what was the purpose of this contest?

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22 months ago, # |
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Awesome competition ! I hacked 12 people on the first task and after that my solution was hacked :)

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22 months ago, # |
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My hacking tests for A were 2 1 1 and 3 1 2.

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22 months ago, # |
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tnx alot!!!

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22 months ago, # |
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Small issue I had: After submitting a hack, the verdict on the hacks page was showing "Waiting" for a long time, it only changed to actual verdict after I refreshed the page.

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22 months ago, # |
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good problems ! wish the recent contest problems were as good as this one

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22 months ago, # |
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It was a hacking contest.... :p

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22 months ago, # |
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As in Educational round hacking time is 24 hour's. It will be better if we are allowed to hack outside of our room and the problem we haven't solve. This is because suppose I have found a tricky case in a problem and I could not overcome it during contest. There may have many solution that passed pretest which will fail in this case.

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22 months ago, # |
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How can we hack solutions after contest or the 24h period isn't for this contest?

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    22 months ago, # ^ |
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    It's for the Educational Round, not this Testing Round.

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    22 months ago, # ^ |
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    24 hour's hacking will be available in Educational rounds.

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22 months ago, # |
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Thanks for the wonderful problems :) Looking forward to the Educational Codeforces Round 1!!

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22 months ago, # |
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can someone please wrap the solution for C into a few words? thanks in advance

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    22 months ago, # ^ |
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    The problem can be solved using dp.

    f[i][k]=number of increasing subsequences of length k that ends at index i.

    f[i][k]=sum f[j][k-1], j<=i, d[j]<d[i].

    You can implement the recurrence using a fenwick tree.

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22 months ago, # |
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I solved A and B in the contest, but it says "Solved: 1 out of 3" on my contest history. Can someone fix it? Thanks in advance :)

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    22 months ago, # ^ |
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    You probably got hacked at last minute :|

    I had that happen to me and that killed my exam really.

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22 months ago, # |
Rev. 2   Vote: I like it +9 Vote: I do not like it

Maybe a bug: number of solved problems in this round is not shown

UPD: fixed

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22 months ago, # |
  Vote: I like it +2 Vote: I do not like it

really awesome :D

I hacked 8 , then I discovered that I made a silly mistake in my code I wished I could hack my self :v

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

Will there be any editorial for Testing Round #12? (for problem-C) Anybody who can share the idea of problem C?

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    22 months ago, # ^ |
      Vote: I like it +6 Vote: I do not like it

    i solved it with dp

    dp[i][j] = number of increasing subsequences that end at number i and has the length of j

    now : dp[i][j] = dp[1][j-1] + dp[2][j-1] + dp[3][j-1] + ... + dp[i-1][j-1]

    u can get the following sum with a segment / fenwik tree

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22 months ago, # |
  Vote: I like it +3 Vote: I do not like it

Please tell me what is wrong with this solution for C here . I used a BIT to calculate sequences of the length j from sequences of length j-1 which ends in a number less than a[i].

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    22 months ago, # ^ |
      Vote: I like it +6 Vote: I do not like it
    idx<=1000006
    

    Shouldn't it be idx <= 100006?

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

      Thank you. I would like to cry now ;;;;;;;___________________;;;;;;;

      It would've been fine in a 1-dimentional BIT. Screwed up because its 2D.

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22 months ago, # |
Rev. 2   Vote: I like it +3 Vote: I do not like it

As these are Educational Rounds , do the tutorials contain an explanation of the algorithms [:. An explanation of the algorithm itself.:] used in the questions, or just tell what algorithm was used [:.Explain Only the problem.:] like the rest of the contests ?

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    22 months ago, # ^ |
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    we hope for the better one!!!!!!

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

    Should be the latter, right? or else the editorial will be huge. Only difference, the explanation of how the algo/data structure is used will be more detailed. eg: if it has a segment tree, then explaining how the generic segment tree update and queries are made will make the editorial triple in size. But explaining the structure of the nodes should probably be there.

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

      To be honest, I expect a pinch of both, Not too Short, Not too Long. Giving little about the background of the algorithm used [:. Enough Info to search and learn from Other Online resources.:] and more on the whys and hows [:.Not only the usual which algo is best but give insight to why it is used specifically (Over others if any) and how it is modified to fit the problem.:].

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

I don't get one thing though... If they want the rounds to be for educational purposes, shouldn't they be based on particular algorithms/data structures/theory ?

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

    Part of solving a problem is figuring out which algo to use. By making it unrated, they are discouraging hacks, and you can focus on the problems instead.

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22 months ago, # |
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but also exercises can be used -- what does this mean?

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    22 months ago, # ^ |
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    I mean that for training purpose we often will use not real problems but just exercises: short and formal task on some specific topic.

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22 months ago, # |
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Suggestion: it could be useful to dedicate every Educational Round to some specific topics and declare it's topic and probably list of literature, don't you think so?

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22 months ago, # |
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can i see the data case which my solution failed on after the contest round has ended ,just like cf routine round(div2 and div1) ?

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19 months ago, # |
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@MikeMirzayanov and all, Wouldn't it be better to give out resources or material for some topics to read, on which the next Educational Round questions would be created. I am kinda beginner and always stuck on last 3-4 problems and in tutorial I find some of them are on the topics I never have read.

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

    But I think knowing the topics on which the problems are based might make it easier to solve! At least I feel so if I know the tag of a problem I am more confident on my solution and thereby Educational round will be like Problem Set to me!

    You can always try up solving! :) I think that is as knowledgeable as it would have been when you knew the topics!

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      19 months ago, # ^ |
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      Think with a beginner's point of view, who hasn't even heard of Suffix Tree. Telling that the problem uses DP won't make it easier to think about how to apply DP. And anyway, more resources can be given out so that some of those topics won't be needed and we need to select out which technique can be used. And yes, the motto of Educational series is to make students familiar with different concepts so there must be some resources given out to learn about them. To compete, there is still other Div rounds.

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14 months ago, # |
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Hi,
I want to join to this series of rounds and I have some questions:
1. Why it named "Educational"?
2. Is there any plan for these rounds? (e.g any discipline for subject of problems which include in a round)
3. Is there any study program to learn the subjects for this series?
4. What is the prerequisite to take part in rounds?
5. Does it need to solve all the problems in previous rounds (up to now) to join this series or not?

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    14 months ago, # ^ |
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    1.The rounds will educate you with variety of problems and the rounds are not rated. 2.I don't think so. 3.Not really.similar things that you study for other competitive coding. 4.Account on Codeforces which you already have. 5.Nope.

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

...

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10 months ago, # |
  Vote: I like it +78 Vote: I do not like it

why there are no educational rounds in recent days ?

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8 months ago, # |
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Let's make educational rounds rated like atcoder. In atcoder beginner contests are rated for beginners. More beginners will participate to rounds.

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

can anyone tell me where i can find the editorial of codeforces educational round 1 .