Hi, I want to share a very interesting proof for the existence of centroid.

Let's direct each edge to the side that has more vertices. (direct randomly if equal) Then you have n vertices and n-1 edges, therefore at least one vertex has an outgoing degree of 0. (If for every vertex the outgoing degree was at least one, we needed at least n edges) This vertex is your centroid. (Because all edges are directed towards it, so no child has more than n/2 vertices).

Using this approach, not only you prove centroid exists, but you can also find it.

I explained it in detail and with visuals in my video on centroid #2 here: https://www.youtube.com/watch?v=t74JJlMIQv8

Recently many people wanted me to talk more about more advanced topics. So I thought maybe I should share this here. (not many people had watched the video)

If you like such facts, let me know. I will make more videos about them.

Let me know about your opinions.

I want to say that if I'm doing anything wrong, I'm sorry. I planned to do something big and make a big positive change, but I received hate in response. I don't think it was fair. But, maybe I was doing something wrong, and I'm sorry about it.

You can read this blog to see what I'm talking about. https://mirror.codeforces.com/blog/entry/125745

I don't intend to defend myself. I just have one request. Help me figure out what I did I do wrong that I'm accused of being unethical here.

Do you want to stop doing it? What should I do?

I was thinking about many things that I might have done.

As kostka mentioned many times, duplicate accounts (Shayan and Algorithms_with_Shayan).

I'm sorry for it. As I mentioned once Algorithms_with_Shayan is not my personal account and I think it is not against the policy. But from now on, I won't do anything in that account anymore. I will have this account. That account can be banned. I'm sorry if I did anything against the policy. Does that resolve it?

My conversation with TheScrasse about the stream.

I never did anything against your consent, my friend. But you tried to show everyone like I used you or something? I don't understand why?

I never share my chats. Here, some part of the chat is exposed in the other blog and some parts are hidden. People are accusing me of using TheScrasse. So I have to show this.

This is how we decided to do the streams. I used anyone? I talked bad with anyone?

I'm sorry if I had done anything wrong.

Please tell me what is the reason you wrote against me so that maybe I can stop it.

Do you want me close my YT channel? Do you want me to stop getting help from others to stream for me? What I am doing wrong that you insult me like this and accuse me of being unethical?

Somebody tells me that I used people. Someone tells me my videos are bad. Someone tells me you are muslim!

The word 'exposed' is used for criminals or at least someone who has done something bad. Right? Can you tell me my crime? Making bad videos?

I can't understand any of these.

I'm not an enemy, tell me what disturbs you and I can stop that.

Hello Codeforces!

We are going to hold some online OI-style contests, the tasks are the selected tasks, chosen from the older Iran national team selection contests.

The level of these contests is around the IOI, maybe a bit simpler, and the main reason of them is to help Iranian students to prepare better for the summer camp contests, which will be held around 3 weeks from now and the national medalists will be chosen there.

And also we did translate tasks to English, so that if anyone from anywhere wanted to prepare for the IOI or other competitions could use it too.

We will have 1 contest per week, and you can freely choose 5 hours to participate in the contest, after each contest the top performers will be announced.

You can participate in contests on the inoi-judge website, the first contest time period starts from Aug 10. 08:00 GMT, There is no need of registration from now, whenever a contest starts you can go and participate in it.

Also, you can see tasks of this year’s contests in the problemset, just keep in mind that you should first login to see the tasks.

And also you can join our telegram channel if you want, further content and posts will be there.

The INOI Team Selection 2021 Online Mirror Competition has ended, now the second-day contest’s tasks are on the judge for upsolving, and statements, editorials, and testcases of tasks released here.

We want to apologize if there were any issues in the contests and thank all the people who gave us feedback.

We had an interesting talk with Zixiang Zhou (duality) who has won 2 gold medals and a silver medal in IOI at age 16 and also got 600 points in our competition. we asked some questions about himself, how he practices and his strategy in the contests. We believe it can be beneficial for everyone. You can see this talk in our telegram channel.

Also, soon we will have online mirrors of our summer camp contests and our Regional ICPC, and some other stuff.

Hope this will be helpful.

Hello everyone!

We are glad to invite you to participate in the Iran National OI Team Selection contests.

Every year in Iran, the Iranian National Olympiad in Informatics (INOI) committee conducts a summer camp to choose 8 top students to prepare them for next year's IOI and a spring camp to choose 4 out of those 8 to form the Iranian national team in IOI.

After the successful experience of holding the mirror of last year’s summer camp contest with few contestants, we are going to have the mirror of our national team selection on a larger scale. The level of these contests is around the IOI, and harder than the contests of the summer camp, and the point of holding the mirror of these contests is to help the IOI participants from other countries to prepare better for the IOI, and Persian younger students to have experience of these contests and prepare better for the future.

Now we want to invite the codeforces community to participate in the contests too.

Two contests will be held, each contest will have 3 problems with subtasks and duration of 5 hours, statements will be available in both English and Persian, you will have 7 days time, first 4 days are for participating and you can freely choose 5 hours to participate in the contest, after this 4 days tutorials will be released and you will have 3 days for upsolving problems, after that, the judge will be down.

The first contest time interval begins from May 29. 08:00 GMT, and the second contest time interval begins from June 5. 08:00 GMT. Contests will be held in inoi-judge, and you can see summer camp problems and other announcements there too, for more announcements and discussions you can join our telegram channel.

The whole ranking will be released after the contests, and the top 8 and the top 8 of Persian students under age 18 will be announced as honorary gold medalists, the dataset will be released for the public too, but if you wanted to use our problems in some contests or training camps, please contact us via iran.oi.judge@gmail.com and inform us.

PS:

The chosen national team this year is:

1. Ali Safari (Amoo_Safar)
2. Alireza Kaviani (alireza_kaviani)
3. Ali Shahali (AliShahali1382)
4. Alireza Keshavarz (Keshi)

In most of these last years we had rank around 3 to 5 in IOI, hope this team will end up with rank 1 or 2 and break our record. :)