Hello everyone!

I would like to invite you to participate in April Circuits '20. It's a long contest that will start on Apr 18, 09:00 PM IST (check your timezone). The contest will run for 7 days.

The problems were prepared by arthur.nascimento, coolreshab, hackslash_123, Ajay Cumar, 2017csb1088 and me. Thanks to Arpa for testing the problems and helping us prepare the problems and MikeMirzayanov for creating Polygon.

You are expected to solve 7 algorithmic and 1 Approximate programming problem over this period and the timeline is as follows:

• Day — 0 Problem 1, Problem 2, Problem 3
• Day — 1 Problem 4, Problem 5
• Day — 4 Problem 6, Problem 7
• Day — 6 Problem 8 (Approximate)
• Day — 7 Challenge ends

New problem statements will be published every 48 hours, and yes, this is a rated contest.

The prizes of this contest will be directed towards COVID-19 relief programs.

To get more information check out this link.

I noticed that most editorials of the last educational rounds will be published 1 or 2 days after the contest. Of course, I have nothing against it, but at all one trivial question, why?

Despite I am big fan of bitsets, I don't even know what is the exact time complexity. I think operation OR, XOR and etc. works in $$$O(\frac{size}{64})$$$, the explanation is that solutions which used it got AC. But on the other hand, I have read in blogs that there would be $$$32$$$ instead of $$$64$$$. Please help me, what is the exact time complexity for each function and which factors it depends on and explain work principles.

Yesterday, when I was writing virtual contest in GYM, I found some interesting feature. From status I could find number of tests, I guess it works for any problem. However, I have not tested it for official round, but at all it's worth for a new blog. In the status-filter bar, you maybe have seen a section "test", but you probably dont know the magic, which can be done with it.

By changing sign to $$$\geq$$$(is greater than or equal to) and giving number to this empty space you can find number of test. If you found that maximal $$$x$$$, that all submissions are accepted and no submissions at $$$x + 1$$$, $$$x$$$ is the number of test. You may ask, why binary search is written in the title. It's the most optimal and the fastest way to find this number, less than 10 steps)

P.S. Sorry for my poor English

UPD: It works in Official Rounds.

Hello Codeforces community!

If you think that it is impossible to see the status of friends in any particular contest, you are mistaken. I found such a strange bug that you can do this. For example let's take Codeforces Global Round 1. You can't find any "only friends" button in status page of contest. So, if you wanna do this, go to this link. In fact. you can substitute word "magic"(it is in link) to another one, except "A", "B", ... "H" (relate to contest). It's magic!

Sorry for my poor English

Hello Codeforces!

Can someone prove and explain greedy-solution of this problem? Are there any relationships between 13C and 866D?