Hello! Codeforces Round #665 (Div. 3) will start at Aug/20/2020 17:35 (Moscow time). You will be offered 6 or 7 problems (or 8) with expected difficulties to compose an interesting competition for participants with ratings up to 1600. However, all of you who wish to take part and have rating 1600 or higher, can register for the round unofficially.

The round will be hosted by rules of educational rounds (extended ACM-ICPC). Thus, during the round, solutions will be judged on preliminary tests, and after the round it will be a 12-hour phase of open hacks. I tried to make strong tests — just like you will be upset if many solutions fail after the contest is over.

You will be given 6 or 7 (or 8) problems and 2 hours to solve them.

Note that the penalty for the wrong submission in this round (and the following Div. 3 rounds) is 10 minutes.

Remember that only the trusted participants of the third division will be included in the official standings table. As it is written by link, this is a compulsory measure for combating unsporting behavior. To qualify as a trusted participants of the third division, you must:

• take part in at least two rated rounds (and solve at least one problem in each of them),
• do not have a point of 1900 or higher in the rating.

Regardless of whether you are a trusted participant of the third division or not, if your rating is less than 1600, then the round will be rated for you.

Thanks to MikeMirzayanov for the platform, help with ideas for problems and for coordination of my work. Thanks to my good friends Daria ZeroAmbition Stepanova, Mikhail pikmike Piklyaev, Maksim Ne0n25 Mescheryakov and Ivan BledDest Androsov for help in round preparation and testing the round. Also thanks to Artem Rox Plotkin and Dmitrii _overrated_ Umnov for the discussion of ideas and testing the round!

Good luck!

ban c++ from cf bc its too fast and doesnt give a chance to people who want to code in say python to play on an even playfield and sometimes even makes it hard to have a solution that does not tle at all since the offdcial solutions are always c++ and based on that is the TL set

One thing I really like about IOI and similar contests is that everyone gets a printed copy of the problem statements translated in their language.
While I understand that giving a printed copy to every contestant on codeforces would be hard, what stops us from having statements translated to our language?
I do understand english good enough, but sometimes I am unsure and it seems really unfair to me that english speakers have an advantage of this kind, so I propose that rated contests must have their statements translated to every language of participants!

Codeforces Global Round 10 should be unrated for the following reasons:

1. Long queue: the queue was really long (up to 20 minutes)! Imagine submitting a solution for problem A at 0:05 and receiving the verdict "runtime error on test 2" at 0:25 because of a silly out of bounds: it's really unfair!

2. Weak pretests on problems A and B: this is a critical issue of the contest, because more than 20000 submissions on problems A and B passed the pretests! Among these, about 1000 solutions were hacked and more than 1000 solutions failed system tests (more than 2000 people have been affected). Even the model solution was wrong!

3. Also, the leaderboard has been messed up by the enormous number of hacks (hacking 6 people can be worth more than a problem); hacks are unfair because not everyone has the same chances, since some rooms have more wrong solutions than others.

4. Wrong order of problems: the problem F was extremely easy, in fact it was proposed as a B (it's written on the editorial). So, people that were not able to solve E had a significant advantage, since they had the opportunity to try the easy problem F and get a lot of points.

It's obvious that Codeforces Global Round 10 should be unrated!

Sign the petition!!! link

I have a firm belief that the clear lack of women in competitive programming is due not to their inferior brains, but rather to the vast male prevalence that makes them feel out of place.

Some efforts are being made to address this problem, eg Google Code Jam for Women, but in my opinion we are not there yet.

Thus I propose that codeforces, being the most prominent competitive programming platform, make some effort by establishing a weekly contest for women only, so that they may feel safe and not oppressed while coding.

this method (discovered by me!!!) allows to become lgm, but red black trees are very difficult and no one really wants to study them
so I've discovered a new (!) method to become lgm, and it requires no effort (!!!)
now I'll prove that everyone is an lgm

lemma: everyone has the same rating on codeforces
proof by induction: we will prove that every group of $$$n$$$ people has the same rating on codeforces
base case: this is obviously true for $$$n = 1$$$
induction: $$$n \rightarrow n + 1$$$
pick a group of $$$n + 1$$$ people: the $$$n$$$ people on the left and also the $$$n$$$ people on the right have the same rating, so the property is true also for $$$n + 1$$$
so everyone has the same rating (q. e. d.)
so you have the same rating of tourist (!!!)
so you are an lgm (!!!!!)

I am thoroughly convinced that CF should add the option to quit a contest after having already submitted solutions. What if you find out halfway through the contest that you have other appointments and have to leave before the end of the competition? It just doesn't make sense to lose rating in such a way.

please stop putting so many constructive problems in all contests

today's contest
1392A - Omkar and Password constructive
1392B - Omkar and Infinity Clock constructive
1392C - Omkar and Waterslide constructive
1392D - Omkar and Bed Wars constructive
1392E - Omkar and Duck constructive
1392F - Omkar and Landslide constructive
1392G - Omkar and Pies constructive
1392H - ZS Shuffles Cards constructive + math
1392I - Kevin and Grid constructive

what is the color of lgm? red and black
is there anything red and black in competitive programming? yes, red black tree
so it's enough to learn red black tree to become lgm!!!
red black tree tutorial

geometry problems are the most interesting and beautiful problems in competitive programming, but they are so rare
these contests are wonderful: geometry contest 1, geometry contest 2
having geometry contests regularly on codeforces (and also a rating only for geometry) would be fantastic

system tests should be abolished

if the code passes the pretests, it should definitely be accepted

otherwise the leaderboard is messed up, jqdai0815 doesn't deserve the first place!!!!!

how to continue these sequences?

seq 1

6 50 952 53916 2927820 884840754 397485028540 ?

seq 2

3205 3209 3216 3223 3229 3295 3376 3553 3681 3735 ?

MikeMirzayanov and codeforces community, help me plz, it's for my friend!!! I need at least other 20 terms of the sequences!!!

I noticed two users who have cheated in this Round (Educational Codeforces Round 92) and I want to name them here. I request the Codeforces community to take strict action against them those who degrade the quality of this beautiful platform. With internship season round the corner, Codeforces is often taken as an accountable platform by Companies and these people should be punished.

Their handles are: armypellegrini, avendraminiOfficial

This is so disgusting.

Look at their submissions. They use very tactful tricks to avoid plagiarism checks, such as swapping lines and changing the name of the variables, but the logic of their code is identical. I request the community here to take strict action on them. Please ban their accounts permanently.

For Problem B: 88318820 88327149

For Problem C: 88332428 88339169

And this didn't happen only in this contest, most of us struggle to become green, instead it seems that avendraminiOfficial is blue only thanks to the help of armypellegrini! He even got "skipped" verdict and no rating change in a contest because he was performing badly and he asked the help of his batchmate, instead he deserved a huge rating drop! 83646680

Besides, I would also request the community here to look forwards towards more efficient plagiarism checks. Such rackets will continue to occur if we don't take an action. Codeforces is trusted because people don't cheat here. I hope that accountability is still maintained and strict action is taken against these handles.