Hello.

As you already know the round was declared unrated. Firstly, we're extremely sorry that this happened and hope you enjoyed solving the problems regardless.

About what happened, the constraints for B were $$$t = 100$$$ and $$$n = 1000$$$ from the beginning i.e. for more than a month. This problem was supposed to be A initially, so I kept lower constraints than usual to ensure a small queue. At the same time, I didn't want trivial brutes to pass, so $$$n = 1000$$$ seemed like a good choice. Around 1 hour before the contest, a tester reminded me of his earlier feedback about increasing the number of test cases and adding a constraint on the sum of $$$n$$$, which would also make it more clear whether $$$\mathcal{O}(n^2)$$$ solutions should pass or not. At the same instant, I gave him WRITE access on polygon so that he could review all the problems.

Unfortunately, there was some miscommunication on my part leading him to think I have asked him to update the constraints. As a result, he updated the test data and the statement immediately, while I was busy doing last-minute checks. The problem was not intentionally updated during the round; he was under the impression that the contest starts $$$1$$$ hour later than it actually did because of a miscalculation due to Day Light Saving time in his country. As a result, a lot of people were solving problem for old constraints when in fact they were new while some also got RE.

Finally, please understand that this is an explanation of the events and not an excuse. I completely realize that such discussions should happen at least a day before the round, not an hour before. This was a result of many minor lapses, which all unluckily accumulated. I, Anton and, especially, the testers have put a lot of hard work into this round over the last $$$3$$$ months; the testers continuously pushed us to improve the quality of the contest through their honest feedback about the problems and overall difficulty, as well as improvements to the statements. Please do not blame them.

Once again, I am really sorry about this and hope you understand.

Thank you for participating, and I hope you enjoyed the problems! Once again, we're sorry about the round being unrated.

Also, here are video editorials by BRCode:

• Problem A and B
• Problem C
• Problem D
• Problem E
• Problem F

This problem was set by Anti-Light and prepared by knightron00

Good Evening Codeforces! ^_^

This round is unrated; please read this to know why.

I invite you to participate in Codeforces Round #682 (Div.2) taking place on Nov/13/2020 17:35 (Moscow time). The round, authored by Anti-Light and me, is rated for users rated less than 2100, while other users can participate non-competitively.

The round features six problems, and you have 2 hours to solve them. There may, or may not, be an interactive problem; regardless, you should know how to deal with them.

I would, now, like to thank–

• antontrygubO_o for coordination.
• AwakeAnay and AsleepAdhyyan for helping me solve one of the problems.
• BRCode for making 3b1b-style video editorials of the problems!
• knightron00 for helping with preparation.
• Devil, Dragnoid99, far_from_NOOB, IaMaNanBord, Osama_Alkhodairy, prabowo, taran_1407, Tarrus, Tathagat_shah, TheOneYouWant, Utkarsh.25dec, Vivek1998299, _Aaryan_, aryanc403, dorijanlendvaj, coderz189, hugopm, kshitij_sodani, ltc.groverkss, nishkarsh, Roham, shash42, socho, talibmohd, thenymphsofdelphi, Monogon, Ari, 300iq, AmShZ, errorgorn, tejas10p, solvemproblr, DumbbAlgo, aujasvit_datta, TeaTime, stack_overflows, manik.jain, namanbansal013, Gur27, and DarkCraftPlayz for testing!
• MikeMirzayanov for Codeforces and Polygon platforms– Polygon is still remarkable!

We will announce the scoring distribution shortly. The scoring distribution is 500–750–1250–1750–2250-3000.

Good luck, and stay safe!

UPD: Editorial

For students in high school or below—

Participants who are currently in high school or below are eligible to win prizes — 25 USD gift cards to 5 random participants who solve at least 3 problems. Prizes are sponsored by Athena Education and are NOT related to Codeforces. To be eligible, please fill this form (it will be closed after the round ends). If you're interested in participating in other technical events, such as Machine Learning and Computational Linguistics, please head over to exunclan.com.

Hello everyone!

Similar to last year, these are the country standings for IOI 2020 based on the sum of scores of all contestants. Check the spoiler at the bottom for the complete list.

Thank you for participating, and I hope you enjoyed the problems!

Also, here are video editorials by BRCode:

• Problem A and B
• Problem C
• Problem D
• Problem E

Code: 89479484

Code: 89479612

Henlo Codeforces! ^_^

I invite you to participate in Codeforces Round #663 (Div.2) taking place on Aug/09/2020 17:35 (Moscow time). The round is rated for users rated less than 2100, while other users can participate non-competitively.

The round features five problems, and you have 2 hours to solve them. There may, or may not, be an interactive problem; regardless, you should know how to deal with them.

I would, now, like to thank–

• antontrygubO_o for coordination and manipulation.
• AwakeAnay, AsleepAdhyyan, and RestingRajarshi for always listening to my problem ideas.
• BRCode for making 3b1b-style video editorials of the problems!
• Aggu_01000101, Devil, Dragnoid99, far_from_NOOB, IaMaNanBord, Osama_Alkhodairy, prabowo, taran_1407, Tarrus, Tathagat_shah, TheOneYouWant, Utkarsh.25dec, Vivek1998299, _Aaryan_, aryanc403, dorijanlendvaj, coderz189, hugopm, knightron00, kshitij_sodani, ltc.groverkss, nishkarsh, Roham, shash42, socho, talibmohd, and thenymphsofdelphi for testing!
• MikeMirzayanov for Codeforces and Polygon platforms– Polygon is truly remarkable!

Please do not mind the long list of testers (I had to write code to tag everyone here) since the problem set changed significantly after the first round of testing.

We will announce the scoring distribution shortly. The scoring distribution is 500–750–1250–2000–2750.

Good luck, and stay safe!

UPD: Editorial

Here are video editorials by BRCode:

• Problem A and B
• Problem C
• Problem D
• Problem E

UPD2: Finally, congratulations to the winners!

Div. 1:

1. tmwilliamlin168
2. risujiroh
3. fanache99
4. LayCurse
5. Sugar_fan

Div. 2:

1. 00000010100001100111
2. PouyaNavid
3. 420iq
4. I_want_2400
5. silxi

We invite you to participate in CodeChef’s July Lunchtime, running this Saturday, 25th July, from 7:30 pm to 10:30 pm IST. The contest features 5 problems and is 3 hours long.

Also, if you have some original and engaging problem ideas, and you’re interested in them being used in CodeChef's contests, you can share them here.

Here is the problemsetting panel:

• Setters: Aman Retired_cherry Dwivedi, Shyam codemaster3840 Bajaj, Ahmad ahmad_salah Salah, Shashwat SleepyShashwat Chandra
• Admin : Teja teja349 Vardhan Reddy
• Tester: Yash yashChandnani Chandnani
• Editorialist: Rajarshi RestingRajarshi Basu
• Statement Verifier: Jakub Xellos Safin
• Mandarin Translator: Gedi gediiiiiii Zheng
• Vietnamese Translator: Team VNOI
• Russian Translator: Fedor Mediocrity Korobeinikov
• Bengali Translator: Mohammad solaimanope Solaiman
• Hindi Translator: Akash Shrivastava

Prizes:

The top 10 Indian and top 10 Global school students from ranklist will receive certificates and CodeChef laddus, with which they can claim cool CodeChef goodies. Know more here.

Good luck and have fun!

Hello Codeforces!

Today my friend Anay changed his handle to AwakeAnay and I can't stop laughing.

What are the most terrible handles you know of?

Greetings Codeforces Community!

I would like to invite you all to participate in the Exun 2019 Programming Prelims. The contest will be 2.5 hours long and will contain 6 problems. All the problems will be from IOI Syllabus.

The contest is rated for everyone.

The problems are prepared by Tarrus, AwakeAnay and me. I would also like to thank taran_1407, arjunarul and the rest of the CodeChef team for helping with testing and reviewing the problems.

Contest Details:-

• Start Date and Time : 11th October 2019 (19:30 hrs) to 11th October 2019 (22:00 hrs). (Indian Standard Time — +5:30 GMT) — Check your timezone
• Registration: You just need to have a CodeChef handle to participate. All those who are interested and do not have a CodeChef handle are requested to register in order to participate.
• Registration for Onsite Finals : All Indian School Students are eligible for the onsite finals at Delhi Public School R.K. Puram, you can register here and then fill this form.
• Prizes: Top 10 performers in the Global and Indian category will get CodeChef laddus, with which the winners can claim cool CodeChef goodies.Other than that, five random participants and the first user to solve each problem will also get CodeChef laddus.
• The ranklist will be IOI style.

Good Luck!

Hope you enjoy solving the problems!