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

Dear girls and women! Happy Women's day! On behalf of the Codeforces team I would like to wish you all the best!

May love and care surround you! May you always catch the admiring gazes of men! Stay beautiful and clever and keep making us happy!



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By MikeMirzayanov, 7 years ago, translation, In English,
I propose to discuss here all that concerns Codeforces Beta Round #3. Of course, during the competition it is forbidden to write anything about the solution of problems and similar things  

For the time of this contest, we turned off the chat server. This does not mean that it will not operate in future - I think it is a convenient and efficient way to communicate during the competition and you may expect it in the future.  

Also I'd like to announce Codeforces Beta Round #4, which will be held next week. It will be for participants from the second division (non-rated users or those having less than 1500 rating points). We will try not to delay Codeforces Beta Round #5, which will be opened for all. 

Wish you high rating,
MikeMirzayanov

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Announcement of Codeforces Beta Round #3
 
 
 
 
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By MikeMirzayanov, 7 years ago, translation, In English,

It seems everyone is in the know that Codeforces Beta Round#3 didn’t take place in the appointed time. Seemingly, it happened because of the increased popularity of the site, on the one hand, and some of our bugs, on the other. For sure, it’s a pity that things went in such a way. On the other part, if everything had failed during the contest, it would have been worse. The contest is rescheduled for Sunday, 15:00 (Moscow time). Please be sure to check here for the start time in your time zone: http://www.timeanddate.com/worldclock/fixedtime.html?&day=07&month=03&year=2010&hour=07&min=00&sec=0&p1=179

I’d like to remind you that the project is in Beta yet, and we’ll work on the problem and try to fix it.

Thanks for your understanding,
MikeMirzayanov

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

According to The November Revolution of Colors and Titles, the text below is not an actual and just a historical document.

Not so long ago a new rating system was introduced at Codeforces. To complete the picture I’ll tell you about our Table of Ranks.

From this moment on all the participants will be given ranks that reflect their skills and abilities at such a hard field as computer science and problem solving. Judging by the results of previous rounds you will gain (or lose, I hope it’s not your case) points. If you score big success, you are promoted to a higher rank. You can see the dependence between rating and ranks in the table below. Moreover each rank has its color, which is reflected in the table.

RatingRank
0-1199Recruit
1200-1349Corporal
1350-1499Sergeant
1500-1649Lieutenant
1650-1799Captain
1800-1999Major
2000-2199Lt. Colonel
2200-2399Colonel
2400-2699General
2700+Marshall

As you have already noticed: we have only three captains in our regiment: vepifanovgusakovRAVEman. But I’m sure, after Codeforces Beta Round#3 we’ll have a number of promotions.

Wish you high rating,
MikeMirzayanov

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By MikeMirzayanov, 7 years ago, translation, In English,
Codeforces will be unavailable for up to 6 hours while we upgrade our infrastructure (March 3, 4PM - 10PM). Thank you for your understanding.

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By ivan.popelyshev, 7 years ago, translation, In English,

Intro

Every high school or college coach quickly comes to mind about his own online judge system. We can deal with huge systems like  e-judge or pcmc-2, we can make something our own like contester or acmp, but in any case to create a contest we should

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By AndrewLazarev, 7 years ago, In English,

Problem A. Winner


To solve the problem we just need accurately follow all rules described in the problem statement. Let's describe in more details required sequence of actions.
  1. First of all, we need to find the maximum score m at the end of the game. This can be done by emulating. After all rounds played just iterate over players and choose one with the maximum score.
  2. Second, we need to figure out the set of players who have maximum score at the end of the game. We can do this in the same way as calculating maximum score. Just iterate over players after all rounds played and store all players with score equal to m.
  3. And the last, we need to find a winner. To do this we will emulate the game one more time looking for player from the winner list with score not less m after some round.
This task demonstrates that sometimes it is easier to code everything stated in the problem statement, than thinking and optimizing.

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By ivan.popelyshev, 7 years ago, translation, In English,
Lets start from the end.

Problem С. Commentator problem

Let R be the distance from point А to a circle with center О and radius r. From this point the circle is observed at the angle .
So, the three stadiums are observed at the same angle if R1 / r1 = R2 / r2 = R3 / r3.
Take two different points A, B. The set of points C that AC / BC = const is either a line (perpendicular bisector of AB) or a circle with center somewhere on the line AB. This circle is easy to find. It contains two points that lie on AB and satisfy AC / BC condition.

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

As some users have already noticed - contest rating has been added to Codeforces. For now it is in beta too, but it looks very adequate. Here's how it is calculated.

Each person is characterized by their rating, the number R. If person A's rating is RA, and person B's is equal to RB, then the formula


gives the probability that A will get a higher position than B in the round final standings. By the way, here everything is very close to the Elo rating.

Before updating your rating after the end of the round, for each participant his seed is calculated, that is the place that the participant is expected to take in this competition. Thus, two things are known for each participant - his seed (the expected place) and rank (the actual place). Depending on the difference between these two values, your rating increases or decreases. If the difference is higher, your rating changes more.

There are a few technical points:

  • if it is the first contest for a participant, his seed is calculated as 1 + n / 2, where n is the total number of participants in the round;
  • changes in the ranking of contestants are multiplied by a correction factor such that allows the sum of ratings of the participants to remain unchanged (before and after the round).

As at TopCoder all users are divided into two divisions: the first (rating over 1500 1650) and the second (rating_ not more than 1500 1650). Not rated users fall into the second division automatically.

Wish you high rating,  

MikeMirzayanov

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

Thank you all for participating in Codeforces Beta Round # 2. I hope you enjoyed it. You may discuss the problems and system in comments. Please express your opinion, especially if you notice any inappropriate behavior. And as always, I will read with interest the suggestions for improvement.

Congratulations to the three leaders: RAVEman, GarnetCrow and ivan.popelyshev!

See you at Codeforces Beta Round # 3.

P.S. And by the way, the round tutorial is waiting for a volunteer. It is desirable that it will be one of the leaders of today's competition. The tutorial should be in Russian and in English. It will be published on the homepage and later will be available via special link from the contest page.

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Announcement of Codeforces Beta Round #2
 
 
 
 
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