TL;DR

What if we introduce the followings:

• You'll have a register-as-unrated button. You can switch rated and unrated only before opening a problem.
• If you are registered as a rated participant, you'll get rated when you open a problem, even if you don't submit.

Hello, community.

Currently, your AtCoder rating changes only if you submit to the contest. This is also the case with Codeforces, so I think it's a standard.

However, this scheme clearly has a flaw; you can leave the contest without submission to keep your rating. This implies you may get underrated because of those who didn't submit. You would say things like this can happen only if you are a newcomer, and the effect will be negligible in the long term. I generally agree with it, but sometimes even reds are affected by this issue. I know some people intentionally submit CE code to make them rated. At the same time, I know some people do the "Head to F" strategy or similar things and sometimes don't make a submission.

I'm not that harsh to such behavior; rating is just an Internet point. Nonetheless, it's worth thinking about a new system. What I came up with is the following:

• You'll have a register-as-unrated button. You can switch rated and unrated only before opening a problem.
• If you are registered as a rated participant, you'll get rated when you open a problem, even if you don't submit.

I think these options can fulfill most of the participants' requests. For example, if you can't fully participate in a contest or just want to watch it, you can register as unrated participants and even submit during the contest (but don't get rated, of course). How do you think about this?

We will hold KEYENCE Programming Contest 2021.

• Contest URL: https://atcoder.jp/contests/keyence2021
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210116T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: camypaper, maroonrk
• Tester: tempura0224 maspy
• Rated range: — 2799

The point values will be 300-400-500-700-700-1000.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 111.

• Contest URL: https://atcoder.jp/contests/arc111
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210109T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: yosupo sigma425
• Tester: yosupo sigma425 maroonrk
• Rated range: — 2799

The point values will be 300-400-600-600-800-1000.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 110（Sponsored by KAJIMA CORPORATION）.

• Contest URL: https://atcoder.jp/contests/arc110
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201205T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: gazelle
• Tester: satashun kobae964
• Rated range: — 2799

The point values will be 300-400-500-600-800-900.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 109.

• Contest URL: https://atcoder.jp/contests/arc109
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201128T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: nuip
• Tester: yamunaku maspy
• Rated range: — 2799

The point values will be 300-400-500-600-700-900.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 108.

• Contest URL: https://atcoder.jp/contests/arc108
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201121T2100&p1=248
• Duration: 100 minutes
• Number of Tasks: 6
• Writer: camypaper
• Tester: satashun tempura0224
• Rated range: — 2799

The point values will be 300-400-500-600-700-900.

We are looking forward to your participation!

We will hold AtCoder Grand Contest 049. This contest counts for GP30 scores.

• Contest URL: https://atcoder.jp/contests/agc049
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201114T2100&p1=248
• Duration: 200 minutes
• Number of Tasks: 6
• Writer: maroonrk, yosupo
• Tester: yosupo, sigma425
• Rated range: 1200 -

The point values will be 400 — 600 — 800 — 1000 — 1600 — 2400.

Please note that the contest duration is unusually long.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 107.

• Contest URL: https://atcoder.jp/contests/arc107
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201031T2100&p1=248
• Duration: 100 minutes
• Number of Tasks: 6
• Writer: maroonrk, yosupo, sigma425
• Tester: maroonrk, yosupo, sigma425
• Rated range: 0 — 2799

The point values will be 300 — 400 — 500 — 600 — 800 — 900.

We are looking forward to your participation!

We will hold AtCoder Grand Contest 048. This contest counts for GP30 scores.

• Contest URL: https://atcoder.jp/contests/agc048
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201018T2100&p1=248
• Duration: 150 minutes
• Number of Tasks: 6
• Writer: maroonrk, sugim48
• Tester: latte0119, reew2n
• Rated range: 1200 — inf

The point values will be 300-700-700-900-1500-2200.

We are looking forward to your participation!

ARC is back!

(The problem set is organized by rng_58, but it seems that he forgot to write a blog. Thus I do it instead.)

We will hold AtCoder Regular Contest 104.

• Contest URL: https://atcoder.jp/contests/arc104
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20201003T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: satashun
• Tester: tempura0224, kobae964
• Rated range: ~ 2799

The point values will be 100-400-600-700-700-1000.

We are looking forward to your participation!

This contest is CANCELLED. Please read updates for details

We will hold ACL Contest 2.

• Contest URL: https://atcoder.jp/contests/acl2
• Start Time: TBD
• Duration: 150 minutes
• Number of Tasks: 6
• Writer: maroonrk, yosupo
• Tester: maroonrk, yosupo, sigma425
• Rated range: 1200 — 2799

The point values will be 300-600-700-900-1300-1900.

The concept of this contest is the same as ACL1, so you may refer to the announcement of ACL1 for more details.

We are looking forward to your participation!

UPD:

We decided to postpone the contest. The new date is not confirmed, but it is likely to be 3rd October.

The reason for this sudden decision is the collision of the problem with today's Japanese contest (problem). This task is almost the same as our E. We thought if we were to hold the contest with current problems, it would favor Japanese competitors too much.

Sorry for the inconvenience; we appreciate your understanding.

UPD2

We regret to inform you that we discussed the issue and concluded that it is hard to hold ACL2. If we replace E with another problem, you can easily deduce from the point values that these 300,500,700,900,1900 pointers do not need FFT, and the other one is likely to require it. We thought this would spoil the contest, and we tried to find a way to avoid this situation. However, we concluded that it's hard to keep going with this problem set. Therefore, we decided to use the tasks in future contests (of course, we will not use them all together).

rng_58 is now preparing a makeshift contest named Junior ACL (or something), which also uses AtCoder library but is much easier than the original ACL contest. This contest is more like yet another ABC and rated for <2000. The contest will be educational for beginners, but please don't expect ad-hoc, original problems (so it won't be interesting for D1 people; however, it may be useful if you want to test the usage of the ACL library). He said he would finish the preparation quickly and hold the contest tomorrow (or today in the Asian timezone), that is, the same time and date as the original ACL2! Watch out for the announcement from him.

Again, we are very sorry about this. We hope to see you in our next 2800 rated round, which will happen next week.

We will hold ACL Contest 1.

• Contest URL: https://atcoder.jp/contests/acl1
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200920T2100&p1=248
• Duration: 150 minutes
• Number of Tasks: 6
• Writer: maroonrk, yosupo, rng_58
• Tester: maroonrk, yosupo, sigma425
• Rated range: 1200 — 2799

The point values will be 300-600-600-800-900-1800.

As mentioned in this blog, you may use the library in the contest. However, it's not mandatory to install the library or learn C++; I've verified that all problems can be solved with python(pypy3).

I also tried hard to ensure the quality of the problems, and I believe that you can enjoy tasks as a usual AtCoder contest, rather than yet another practice contest. In addition to that, I would like to mention the last problem, which is unusually hard for ARC-rated contests, and we welcome >2800 coders to challenge it.

We are looking forward to your participation!

I've hacked all AC solutions of this problem, which were submitted during the contest, and I believe I can hack most of upsolving solutions. Currently, I only checked that they time out on my local machine, because "Unexpected Verdict" prevents me from uphacking. I even hacked model implementation in the editorial.

Here's my latest generator. Feel free to challenge it.

Side Note: yosupo wrote a solution, which passes the above case, but I failed it with another generator.

What I want to argue is that TL of this problem is too tight, and it affected some of the competitors. For example, I got almost the same idea as the model solution during the contest. Still, I was too scared to write it because I suspected it would time out without full optimization and possibly some tweaks like shuffling vertices/edges or contracting vertices. As I proved it myself, my thought was correct. However, this observation didn't help me, and some people who didn't think of this (or believed the weakness of the test) passed F, which seems unfair to me.

I'm not saying the round should be unrated; I think there exists a really well-optimized solution that can pass all tests. But please, problem setters and coordinators, you should give careful consideration to TL of problems. Don't set the TL by how fast your solutions run on your test. I wish future CF writes and coordinators read this, and that's the reason why I posted it as a separate blog, not a comment to the round.

P.S. Please notify me when you believe your solution can pass all tests, I'll try to challenge it.

We will hold AtCoder Grand Contest 045. This contest counts for GP30 scores.

• Contest URL: https://atcoder.jp/contests/agc045
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200607T2100&p1=248
• Duration: 150 minutes.
• Number of Tasks: 6
• Writer: maroonrk

• Rated range: 1200 ~

The point values will be 400-800-800-1200-1200-1800.

We are looking forward to your participation!

P.S. The AtCoder Race Ranking can be found here. I don't know who created this list, but I'd like to say thank you to them.

We will hold NOMURA Programming Competition 2020.

• Contest URL: https://atcoder.jp/contests/nomura2020
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200530T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: kobae964, satashun, gazelle
• Rated range: ~ 2799

The point values will be 100-200-600-700-900-1000.

We are looking forward to your participation!

P.S. We are planning to set a lower bound for the rated range of AGC, so if you want to reach 2000 before the AGC next week, this contest will be a good opportunity for you.

Hello!

Opencup GP of Tokyo will be held tomorrow, with the same problems as tomorrow's MW-prefinal contest.

The writers are yosupo, sigma425, and me. I will post the editorial after the contest.

We are looking forward to your participation!

UPD The contest is over. Thank you for your participation!.

editorial

UPD2 I managed to load the contest onto the Gym. I'm sorry that the statement doesn't look pretty since it was originally written in markdown format. This is my first attempt to make a Gym contest, so there might be a mistake. If you find some problem, please let me know.

We will hold AtCoder Grand Contest 043. You may confuse this with AGC042, but it is 043. AGC042 was prepared as a mirror of WTF 2020 and we keep it as is.

This contest counts for GP30 scores.

• Contest URL: https://atcoder.jp/contests/agc043
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200321T2100&p1=248
• Duration: 150 minutes
• Number of Tasks: 6
• Writer: yosupo, maroonrk, sigma425
• Rated range: All

The point values will be 400-700-900-1200-1400-2100.

We are looking forward to your participation!

We will hold "Social Infrastructure Information Systems Division, Hitachi Programming Contest 2020".

• Contest URL: https://atcoder.jp/contests/hitachi2020
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20200308T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: tempura0224, heno239, beet, kort0n
• Rated range: ~ 2799

The point values will be 100 — 200 — 600 — 800 — 900 — 1100. We are looking forward to your participation!

Hello, Codeforces!

I have news today: I joined the AtCoder team and started working as an admin. It does not mean I take rng_58's place right now. I'm just a beginner as an admin, so, for the time being, we will hold contests together, and I will learn how to do it.

For this year, I don't stop participating in all AtCoder contests(especially AGCs) and aim to get a ticket for the WTF2021. I will mainly supervise ARC-level contest (and Japanese local contests).

From next year, I'll start checking submitted problems from all writers and organize contests as main admin.

Tomorrow's ARC-level contest is the first contest coordinated by me (with the help of rng_58). I'm looking forward to your participation!

The problem is now resolved. See the comment on the top.

According to the instruction sent by the ICPC WF organizer, we should upload team reference document by 25th March.

However, when I opened the WF team dashboard and clicked "Attachment", anything like uploading button didn't appear. My friend joisino said he couldn't upload his document as well. Thus I think it's a problem with the webpage, but I'm not sure.

Have you succeeded in submitting your document? Please let me know.

Hello everyone!

I have a question. Have you ever participated in a worldwide onsite contest without a US layout keyboard? I've never, but I will!

The upcoming ICPC WF 2019 provides keyboards with Portuguese layout. (source)

Ok, it can happen that US keyboards are not available. For example, in IOI 2016 in Russia, provided keyboards have a Russian layout. However, at that time, participants were able to bring their own keyboards and I was comfortably taking part in the contest.

But in the next ICPC WF, we are not allowed to do that. All we can do is to bring stickers!

I wonder why the organizers made such a decision. I think it's disastrous. Our team practiced very hard with a keyboard with US layout. I'm sure that our (and most of other teams') performance will be affected by this issue. I believe that the organizers should let us bring our own keyboards if they fail to provide US layout keyboards.

How do you think about this issue? I want to hear the community members' opinions (and, if possible, the organizers' opinions).

Thank you in advance.