Codeforces Round #645 (Div. 2) _Сoronavirus work, coronavirus school, coronavirus rest, coronavirus time spending, coronavirus contest._ <p align="center"> <img src="/predownloaded/21/49/2149d863ac14b6520c81bebd44b1d0e544b44eb2.jpg"> </p> Hello, Codeforces! [contest:1358] will start at [contest_time:1358]. This round will be **rated for the participants with rating lower than 2100**. You will have **2 hours** to solve **6 problems**. Problems of this round were prepared by Alexey [user:Alexdat2000,2020-05-19] Datskovskiy, Ilian [user:ilian04,2020-05-19] Andrianov, Vsevolod [user:Sevlll,2020-05-19] Lepeshov. We have made an effort to create interesting problems, beautiful statements and strong tests. We wish you like problems and your rating increase. We would like to express our gratitude to: - [user:MikeMirzayanov,2020-05-19] for wonderful platforms Codeforces and Polygon! - [user:300iq,2020-05-19] for excellent coordination and helpful advices! - Thanks to [user:Siberian,2020-05-19], [use...

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Some notes on rating inflation ### Introduction Recently there have been several suggestions that there is significant rating inflation now due to COVID-19. The typical hypothesis seems to be along the lines of: > Because people stay at home more now, there is a lot of new inexperienced users who add a lot of rating to the system, pushing "old" users upwards without actual improvement. A simplified and a bit more general hypothesis that I'm going to test: > Because of the virus I'm gaining more rating than usual without working more. But most of these comments are based on anecdotal evidence, which is not worth much. I wanted to see if there is any truth to these claims. Specifically, this blog is an implementation (although I modified the approach a bit) of the following [comment](https://mirror.codeforces.com/blog/entry/20638?#comment-601634) by [user:geckods,2020-04-15]:  [cut] $~$ ### Methodology Let's define the "test period" and "control period". ...

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Coronavirus — Overcome the Psychological Stress by Coding My video on the topic: [Shameless Self-Promotion](https://www.youtube.com/watch?v=CFagJwWW7ys) Have you ever noticed how disasters have a weird way of making things better, once the initial problem is contained? Yes, the virus is unpredictable, has deadly potential, and should be of great concern to just about every human on the planet. So, what could possibly be a positive consequence of a life-threatening disease? #### _**1. Code (and live) for the present, not for that offer**_ Yes, these are not the best of times, but a time to reflect on who we are and what is most important in life. For some countries, economy is at risk. But most of Software Engineer jobs give you the opportunity to work remote/from home. Either you have or not a job at the moment, you are not so pressured by this thought anymore. Maybe you come to the conclusion programming is not what you want to do in life anymore. Maybe it's photography, cooking or pottery (Brad Pitt pff..). Or maybe th...

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Летний интенсив от Умника TL;DR Онлайн летняя школа от меня. 5 дней / 4000 рублей. <s>Due to Coronavirus</s> я не смогу этим летом преподавать в летней школе, поэтому решил попробовать сделать что-то похожее онлайн. Как выглядит один рабочий день: 1. Я собираю контест из задач, которые мне кажутся полезными/интересными. 2. Вы их (не) решаете. 3. Я провожу разбор, но на самом деле это повод предметно поговорить о каких-то техниках. 4. Вы дорешиваете контест. Если нужна помощь или хочется что-то обсудить &mdash; пишете в личку или чат. Требования к участникам (в порядке убывания важности): 1. Желание работать. 2. Стабильный интернет. 3. Фиолетовый/оранжевый на кф. 4. 4000 рублей. Технические детали: 1. Контесты в виде мэшапов на кф, продолжительность около 4 часов. 2. Разборы в Zoom. 3. Общий чат и личка в телеграме 4. 3+2 рабочих дня, между ними выходной. 5. Не более 20 участников, если желающих будет больше, то я выберу сам (и причины объяснять не буду). Ну...

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Hosting IOI 2022 is already stressful -- I plead everyone not to make us more stressful **Disclaimer: all opinions written in this post are purely personal and not tied with any affiliation, organization, or institutional I am working with, including but not limited to the IOI 2022 organizers.** Several members within IOI 2022 organizers might even try to prevent me from posting this. Dear IOI Community in Codeforces, I am writing in Codeforces this time, not in e-mails or IOI 2022 website since I am writing this in personal capacity and should not reflect a formal opinion of the IOI 2022 organizers. As you all might know, IOI 2022 will be conducted hybrid -- it will be hosted onsite, but we understand that it is impossible for some countries to come to Indonesia due to the [current global pandemic](https://en.wikipedia.org/wiki/COVID-19_pandemic), so these countries are still allowed to officially participate online. I am going to be very honest and transparent in this post. This is the first time the IOI has a hybrid setting like this. This poses huge chal...

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Help Greek IOI Team Raise Money to Participate On-site in IOI 2022 **TL;DR** The Greek National Informatics team is holding a crowdfunding campaign to become able to participate on-site in IOI 2022 in Indonesia [Click here to donate](https://gogetfunding.com/help-greek-ioi-team-raise-money-to-participate-on-site-in-ioi-2022/) Hello dear Codeforces community, My name is Oleh Naver and I am from Ukraine. Last month my friend posted a blog on Codeforces about a fundraising campaign for hosting the Ukrainian selections for IOI. First of all, thank you all so much for donating, we are so grateful that we were finally able to host them. Now my dear friends from Greece who have qualified for IOI and helped in our crowdfunding are facing an economical issue. Apparently because the spread of the coronavirus has affected the financial state of businesses and national economies, they can't find sponsors to cover the expenses for them to travel on-site to Indonesia. Let me highlight the importance of participating in on-site Olympiads ins...

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What will happen to ICPC World Finals due to Coronavirus? As coronavirus concerns ramp up, I'm starting to become worried about what ICPC's plans for World Finals are. Many schools (Cornell, Harvard, MIT, Princeton, etc.) are all forcing students to leave campus soon. Giving these conditions, I'm curious what plans for World Finals are going to be. Has anybody heard about any contingency plans &mdash; for example, multiple sites? Alternatively, does anybody know if there's any precedent for what happens in this kind of event?

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Will coronavirus affect IOI? Hello codeforces community. As we know the world is now facing a huge problem, we hear about it everywhere, I am sure even some of you are staying isolated from people because of it. Some events are getting cancelled because of it, and the most important events for our community are also in danger of being cancelled. I am talking about IOI and ICPC WF. I saw some official announcements regarding COVID-19 from both of the events ([ICPC](https://docs.google.com/document/d/1yL49d3Ge83AE0UNBmhOwqJawPX9gct21ud6riX7LIk8/edit), [IOI](https://ioi2020.sg/covid-19/)). I understand that they can't decide anything yet, but I am very surprised not to see anyone discussing the problem here. I personally think there are only 4 possible solutions 1. Host the event, but with less countries participating. 2. Cancel the event 3. Do something online, and do not require people to travel to Russia/Singapore. (The problem here will be trusting participants) 4. Delaying the events (I know thi...

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Legends in statements? After the last round ([contest:1358]), the trouble with problems' statements became quite obvious: many people liked the problem themselves, but legends do not. Some people even started talking about incorrect use of coronavirus theme in the statements, you can read [this post](https://mirror.codeforces.com/blog/entry/77982). It's quite a shame that the announcement and editoral get downvotes because of the legends, because making the legend is the most minor part of the problems, much more effort is spent on generating tests, inventing the problem itself, checking the solutions, writing tutorials, etc.. There are people who want to read only formal statements, and there are those who like to read legends. Unfortunately, the first ones are much more numerous, and some of them rate rounds not by problems, but by negative emotions caused during the contest, and in this case the legend. It is often difficult to write a formal statements in a place with a legend, the participant is ...

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How to reduce the load on the judging software When submitting a solution to a problem, I think most people get the general impression that once you pass 30-40 test cases, you are basically home free, i.e. you are highly unlikely to fail a later test case and can consider the problem solved. Despite this, many problems have upwards of 200+ test cases, which can mean several minutes of grading time in the worst case, not even taking into account time spent in the queue. On a related note, the judging software seems to have been heavily overburdened recently, possibly linked to the coronavirus. I think that a good feature to have would be to allow lots of test cases for problems which are relatively recently added, but once a problem has been solved by ~1000+ people, most of the test cases should be removed to allow submissions to go through quicker. In order to choose which submissions to remove, the system should keep track of how often each test case gets failed. Test cases which are almost never failed should be removed. I ...

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The 17th Zhejiang Provincial Collegiate Programming Contest Now Available in Gym Hello, Codeforces! The 17th Zhejiang Provincial Collegiate Programming Contest has ended last weekend (October 17, 2020). The contest was originally scheduled for April 2020 but was delayed due to the coronavirus pandemic. It was eventually decided to hold the contest online in October. The problems for this contest were prepared by retired ICPC team members of Zhejiang University, and I was the coordinator of the problem-setting group. We are glad to announce that we have published the contest, **[contest:102770]**, in Codeforces::Gym for you to practice. Feel free to start virtual participation or to solve the problems individually. For virtual participation, the contest is 5 hours in length and follows usual ICPC rules. Team participation is recommended, but it is also possible to participate individually. The ghosts of the onsite participants are available, you may take advantage of it. My thanks go to: - Hangzhou Normal University and Zhejiang University, for co-hostin...

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Happy Record Day! Hi First of all congrats too Codeforces community for having more than 23000 participants in an official round If I want to be honest I'm not really okay with Codeforces right now, cause recently its servers went down a lot and even in the contests there's a queue that is really annoying, I have no idea about Codeforces problems or why they don't fix these issues but, as a participant I wanted to ask Mike Mirzayanov to solve these issues (like the one that was solved before about the queues and system test speed, thnx btw ). Cause with COVID 19 out there, I spend most of my time in Codeforces right now, I am sure that there are others that are like me. And last but not least just wanted to end this blog by some beautiful quotes: *Dab when you cough *Dab when you sneeze *Dab to beat coronavirus -Paul Pogba 2020 

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Some minor bugs on Codeforces 1. This hack has been in queue for two weeks. https://mirror.codeforces.com/contest/1335/hacks  2. (also on that page) The time is not localized. Actually this is not a bug, just a missing feature. 3. On the "Complete problemset" page, the Codeforces logo is not updated. Example: https://mirror.codeforces.com/contest/1343/problems -- image:  The logo should be this one.  I thought this is because of caching, but the response header is `cache-control: private,no-cache,no-store,max-age=0,must-revalidate`. For comparison, the brand logo is displayed correctly on the "complete problemset" page of the contests such as [Kotlin heroes](https://mirror.codeforces.com/contest/1297/problems). 4. When a tag is duplicated while posting a blog, this error will appear.  Just a little annoying. Co...

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TCO21 finals will be held online TopCoder recently announced that TCO21 finals are going to be held online. They previously planned to hold them in Orlando, Florida, however, the plans were changed due to the worsening COVID-19 situation in the US and the government's plans to [keep the travel restrictions](https://apnews.com/article/lifestyle-joe-biden-government-and-politics-coronavirus-pandemic-travel-f0c79c7d4da2004d45829ba98af7c199). You can watch the video of the announcement [here](https://drive.google.com/file/d/1RGHEl_HbGKrumU3Nlw3og1oCdOZUy6xX/view).

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Event Postponed - Hello Muscat Programming Bootcamp Hi Codeforces, As part of its prevention of the spread of the Covid-19, the Omani government has taken the unprecedented decision to postpone all international events and to temporarily restrict the entrance to the country for people traveling from territories with coronavirus cases. We regret to inform you that, as a result, the Hello Muscat Programming Bootcamp will, unfortunately, be postponed to a later date. Following last year’s memorable event, we were keenly looking forward to another successful bootcamp. However, as organizers, the safety and wellbeing of our participants is our first priority, so we understand that postponing the event is the best decision for everyone. We’re working closely with our partners to set a new date, and plan to consult all parties involved, including coaches and participants to find the most suitable date for everyone. If you have any questions, comments, or concerns, you can get in touch with us at icpc@harbour.space. We will m...

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Web for Online English contests Dear colleagues, I have implemented a webpage that organizes **English exams online**. Its philosophy is the same as websites organizing online programming contests: **users can also participate by creating the exams**. Thus, it has a cooperative approach. The full standings are displayed at the end of the exam and there is a discussion tab. It is [https://englishmomentum.net/](https://englishmomentum.net/). **It is not necessary to register**, as a guest user is provided by default. Thus, it is free, and with no adds. It has been working for 4 months, organizing 2 exams every week. **Next Sunday, two new exams will be run**. They contain several exercises with interesting alternative views of the Coronavirus crisis. You are invited to participate. Any suggestion will be welcome, too.

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Please Help --- 'Grub file filters - Not Found' I had Dual Boot in my system &mdash; parrot linux and Windows 10. Yesterday , i upgraded parrot ,but after restarting i got stuck in this grub rescue terminal (Error **grub_file_filters not found**), then i watched few videos on internet and tried to fix that , but nothing happened . I checked every drive but i think my window is erased, but good thing is that , i haven't lost my linux data ,they were present in msdos7 ,msdos5 (they were more imp) . Please ,if someone knows how to fix that please help me. I presently don't have a bootable pendrive ,also **because of coronavirus ,all computer repairing shops are closed in my area.** These linux data were very important for me , **i had lost all of my templates (convex hull,graph algo ,etc. ) and few projects** , that's my mistake , i haven't have any backup of it) I searched a lot on internet at various platform ,but found no article to resolve this problem . Also i am unable to participate in any contest ,or study anythi...

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Make Codeforces, not Coronaforces Nice logo Codeforces UwU Love it <3 

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IOI 2020 cancelled because of coronavirus? Will IOI 2020 be cancelled because of coronavirus? There have been a total of 110 cases in Singapore

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Orz Orz To all you Japan, China, Antarctica, Russia, America, India, Botswana, Coronavirus, Everybody ans tourist simps. Orz is the best in Kaomoji. Let's comment about why you like Orz!!!

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