As of now, there is no blog, so I'll post this.

How to solve C Large without complex casework?

We will hold NOMURA Programming Contest 2021(AtCoder Regular Contest 121).

• Contest URL: https://atcoder.jp/contests/arc121
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210529T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: camypaper
• Tester: maspy, yamunaku
• Rated range: — 2799

The point values will be 400-500-500-700-700-800.

We are looking forward to your participation!

Please note that the contest time is one hour earlier than the usual time.

We will hold AtCoder Regular Contest 120.

• Contest URL: https://atcoder.jp/contests/arc120
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210523T2000&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: QCFium
• Tester: maspy, satashun
• Rated range: — 2799

The point values will be 400-400-500-600-700-1600(800).

The full version of the last problem is unusually hard for ARC, so there is an 800-point subtask.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 119.

• Contest URL: https://atcoder.jp/contests/arc119
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210516T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: E869120, square1001
• Tester: maspy
• Rated range: — 2799

The point values will be 300-500-500-700-800-800.

We are looking forward to your participation!

Please note the unusual start time.

We will hold AtCoder Regular Contest 118.

• Contest URL: https://atcoder.jp/contests/arc118
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210509T2205&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: maspy
• Tester: tempura0224, yamunaku
• Rated range: — 2799

The point values will be 300-400-500-700-800-1000.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 117.

• Contest URL: https://atcoder.jp/contests/arc117
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210418T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: E869120, square1001
• Tester: tempura0224
• Rated range: — 2799

The point values will be 200-400-600-600-900-900.

We are looking forward to your participation!

We will hold AtCoder Grand Contest 053. This contest counts for GP30 scores.

• Contest URL: https://atcoder.jp/contests/agc053
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210410T2100&p1=248
• Duration: 180 minutes
• Number of Tasks: 6
• Writer: yutaka1999
• Tester: HIR180
• Rated range: 1200 -

The point values will be 400-700-900-1000-1400-2400.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 116.

• Contest URL: https://atcoder.jp/contests/arc116
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210328T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: kort0n
• Tester: beet, heno239, tempura0224
• Rated range: — 2799

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

We are looking forward to your participation!

We will hold AtCoder Regular Contest 115. Please watch out for the unusual start time (1 hour earlier).

• Contest URL: https://atcoder.jp/contests/arc115
• Start Time: Unusual Start Time (1 hour earlier) http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210321T2000&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: YoshikaMiyafuji
• Tester: maspy, yamunaku
• Rated range: — 2799

The point values will be 300-400-500-600-700-1000.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 114.

• Contest URL: https://atcoder.jp/contests/arc114
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210314T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: satashun
• Tester: gazelle, kobae964
• Rated range: — 2799

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

We are looking forward to your participation!

XXI Opencup GP of Tokyo will be held tomorrow.

I prepared the problems with the help from hos.lyric.

I'll upload the editorial after the contest ends, and also I'll upload the contest to the GYM.

Editorial

GYM

We will hold AtCoder Regular Contest 113.

• Contest URL: https://atcoder.jp/contests/arc113
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210221T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: DEGwer, maroonrk
• Tester: latte0119, reew2n
• Rated range: — 2799

The point values will be 300-400-500-600-800-1000.

We are looking forward to your participation!

We will hold AtCoder Regular Contest 112.

• Contest URL: https://atcoder.jp/contests/arc112
• Start Time: http://www.timeanddate.com/worldclock/fixedtime.html?iso=20210213T2100&p1=248
• Duration: 120 minutes
• Number of Tasks: 6
• Writer: nuip, potetisensei
• Testers: latte0119 reew2n
• Rated range: — 2799

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

We are looking forward to your participation!

Thank you for sharing your opinion on my last blog.

I considered what kind of participants I'd like to honor the most. It was those who have strong confidence and eagerness to take part in contests, not those who care about their rating too much or think like, "what if I can't solve a problem...".

Thus I finally decided to adopt an "open-then-rated" system.

Now it's time to determine the details of the new system. What I'm currently considering is the followings:

• If you try to open a problem in the first five or ten minutes of a contest, you see a Read Problems button, and pressing it confirms your rated participation.
• If you are late (or don't press the button in the first five or ten minutes), you are unrated, but still can read and submit to the problems. Also, your name will be shown in the standings and it counts for GP30 scores.

This is a draft, so if you have a concern or an idea, please share it here.

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.