The XXXI Saint-Petersburg High School Programming Contest took place on 4 November 2023 in ITMO University. It is a regional qualification for the XXIV Russia Open High School Programming Contest which will be held on 11–12 December 2023 in person. The problems were prepared by a committee headed by andrewzta: ba.tasya, VedernikovNV, Thinkbuge, Volkov_Ivan, golikovnik, orz, DishonoredRighteous, Volodya333, polipolinom, GShark, VArtem, peltorator, doreshnikov, Toy_mouse, step_by_step and fedor.tsarev.

There were several qualifications for XXIV Open VKOSHP based on this problemset. Below is the list of them with the links to their standings:

• Internet Selection
• Saint Petersburg
• Republic of Tatarstan
• Udmurt Republic
• Gomel Region
• Republic of Karelia
• Western Siberia

The contest has been added to the gym: The XXXI Saint-Petersburg High School Programming Contest (SpbKOSHP 2023) | Qualification for the XXIV Russia Open High School Programming Contest (VKOSHP 2023).

UPD: ghosts are added to the contest, so that during the virtual participation you could spectate in the Standings how the official participants did.

I participated in Codeforces Round 907 (Div. 2). I believe it could be the first time I was late for a Codeforces Round but still participated in it; however, I solved all problems. The round featured a lot of ideas, which were pretty standard, but it still was kinda nice to discover them here.

You can watch here how I participated in Qualification Round of Yandex Cup 2023 Algorithm.

I participated in Codeforces Round 898 (Div. 4) and, surprisingly, solved all problems.

You can watch the solutions (please, not during the contest!):

Today a horrible thing almost happened: I barely stayed an International Grandmaster on Codeforces after participation in CodeTON Round 6 (Div. 1 + Div. 2, Rated, Prizes!). I would't say I was exceptionally slow or that I solved problems too clumsily, but for some reason the majority of participants near my level were faster than me on these problems.

I recorded a five hour long video about my adventures. If you're interested in a particular problem, follow the timecodes:

If you open a video and see it's low quality, you might want to wait several minutes until YouTube processes the higher resolutions.

UPD. This is high quality now. Please watch!

Dear friends,

Today I tried an experimental format: separate videos. So, today I participated in Codeforces Round 896 (Div. 1) and recorded a screencast, but, unlike the previous times, I did not immediately record the editorials. Instead several videos are dedicated to them. So here are the links:

• https://youtu.be/uuyVZcExbEI — screencast of Codeforces Round 896 (Div. 1);
• https://youtu.be/OFKF3oGhvmE — editorial (and upsolving!) of 1869A - Make It Zero;
• https://youtu.be/JoUOqDvKHuo — editorial (and upsolving!) of 1869B - 2D Traveling;
• https://youtu.be/iS3eusWsx3E — editorial of 1869C - Fill in the Matrix (if you're interested in the coding part, you can find it here: https://youtu.be/uuyVZcExbEI?t=938);
• https://youtu.be/1Vu2RSQg0D0 — editorial of 1869D1 - Candy Party (Easy Version) and 1869D2 - Candy Party (Hard Version) (if you're interested in the coding part, you can find it here: https://youtu.be/uuyVZcExbEI?t=2688);
• https://youtu.be/Zn2OkKlgaG0 — editorial of 1869E - Travel Plan (if you're interested in the coding part, you can find it here: https://youtu.be/uuyVZcExbEI?t=5204);
• https://youtu.be/i4RO3x1fmjA — editorial (and long, long upsolving!) of 1869F - Flower-like Pseudotree.

UPD: I recorded the upsolving of 1869F - Flower-like Pseudotree (see the link above). I guess my explanation was quite fine, but in one case I incorrectly calculated the preconditions, which resulted in WA (223630659) and, subsequently, a huge mess and pain. It is still quite educational stuff though: the first half of the video is just a normal editorial (but, alas, with a technical mistake which should't screw the flow of the problem though), and the second one can teach you how to seek for bugs in problems like this one (with a big number of cases).

Also keep noted that for now the video is low-resolution. It will fix itself in half an hour or so. UPDUPD: the high resolution version has been processed and is available on YouTube.

Today I participated in Codeforces Round 887 (Div. 1). My experience was terrible (I wasn't able to solve 1852A - Ntarsis' Set during the contest, hope it tells you a lot), but it's still recorded, so hopefully it'll be useful for somebody. As usual, during the first half I participate while explaining aloud what and how I do, during the second part I explain more slowly the solutions of Div.1 problems A–D.

Note that the audio is quite high quality, and the high-quality video is coming in a couple of hours (Youtube is still processing it right now).

https://www.youtube.com/watch?v=2Dvi4WdFliM

UPD: The video now is high-quality.

Congratulations to Ormlis for taking the first place in a public Div. 1 Codeforces contest for the first time!

The video is uploaded: https://youtu.be/YdJMH0tVgmM

Today I screencast and explained solutions of problems A–D and F. The video is uploaded to YouTube: https://youtu.be/B48ykX0NpUY

I have to inform that the round quality wasn't exceptionally high: the translation was noticeably Google translated from Russian (for example, представление has at least two meanings — representation or performance, and Google Translate wasn't able to discriminate between these two), the pretests were weak in B, C and F (many people were simply TL-hacked or had their solution fail during system testing). I will elaborate on problem F: there I wrote a square root decomposition with incorrect constants, but still got AC though my solution was incorrect on these simple tests:

2 3
2 2

and

4 24
5 5 5 5

With the first of these, I was able to uphack six accepted solutions, including my own.

Nevertheless I knew what to expect (I call such rounds contests for schoolchildren) and overall experience was satisfactory.

Good Bye 2022: 2023 is NEAR finished, and I participated in it with usual explanations of everything that I do and with editorial of A–E in the end. You're welcome to watch, the video is already on the channel!

https://youtu.be/VBOi99QMfTw

Two days ago Northern Eurasia Finals 2022 took place, mirror of which was on Codeforces: 2022-2023 ICPC, NERC, Northern Eurasia Onsite (Unrated, Online Mirror, ICPC Rules, Teams Preferred). In the next few hours the standings got unfrozen, thereby we know the list of the teams that qualified to the ICPC Finals this year:

1^st place 🏆 MIPT: Yolki-palki (Pechalka, Kapt, Tikhon228)

2^nd place 🥇 HSE: FFTilted (I_love_teraqqq, I_love_kirill22, Ormlis)

3^rd place 🥇 SPb SU: Urgant Team (sava-cska, RedMachine-74, orz)

4^th place 🥇 Belarusian SU: 1: Dungeon Thread (Septimelon, RED_INSIDE, programmer228)

4^th place 🥇 SPb ITMO: pengzoo (iakovlev.zakhar, DishonoredRighteous, golikovnik)

12^th place 🥉 Innopolis: U A (Farhod, sm1lee, Laggy)

14^th place Kazakh-British TU: DeoxyriboNucleic Acid (amanbol, Na2a, DimmyT)

15^th place SPb HSE: Just3Keks (Xrite, vmos1999, NeKpoT)

20^th place Nazarbayev U: wf or gf? (dulatcodes, CMaster, krauch)

23^rd place AITU: 1 (Muratov, Aliaidar, Kamzabek)

24^th place Moscow SU: apes together strong (voyrus, Vladithur, revelcoS)

27^th place BSUIR: #1: So stuffy (kartel, p3rfect, romarkovets)

Congratulations to everyone aforementioned!

I started coding after I discovered LOUD Enough's cp journey, they showed me that all three barracks can fall simultaneously within first ten minutes of Survival Chaos round

so thank you, tranquility, nikgaevoy, Kaban-5 for your introduction to the CP world

In my deepest gratitude I've drawn all three some of you solving questions on Codeforces site

As Makoto Soejima said, never give up!

please don't down vote, it's my first blog post

After a bit of a pause I release a new video on my channel — screencast of explanation Codeforces Round 833 (Div. 2). Although my participation was not that successful, I solved five problems and explained all six problems in the video. Feel free to watch!

turmax orz on becoming an LGM recently!!!

Today demon1999 pleases us with a wonderful holiday — she turned 23 today. Thank her for this!

Today there were two nice contests in a row: AtCoder Regular Contest 149 and Codeforces Round 824 (Div. 2). I participated in both of them.

1. My participation in AtCoder Regular Contest 149 was quite a failure, I neither speedforced nor solved any of the harder problems. The video is already on my channel: https://youtu.be/3D1IbPtrLWg

2. My participation in Codeforces Round #824 (Div. 2) wasn't a failure, I even finished second! (And this is my by far the most successful participation in an unrated round.) The video is uploaded but still processing, so soon you will be able to watch it. As always, a nice bonus is a detailed editorial in the end of the video: https://youtu.be/fbFAg1th5oM

Subscriptions, comments, likes, watches and other ways of expressing feedback are welcome!

UPD. Now both videos are watchable. Enjoy!

Dear everyone,

As always, my screencast and detailed analysis of problems A–G of Codeforces Global Round 22 is already uploaded (but still processing for high-quality viewing) on the channel. This time the video is huge — over five hours!

Please watch, enjoy, learn, comment — anything you want!

UPD. The video is ready for viewing.

Honestly, I don't really like contests carried out by giants like Google and Meta. While participating I feel some sort of permanent malaise, it seems like giants simply ignore all experience of how contests are run by Codeforces and AtCoder. But today I went as far as I have never gone before — I took 201^st place at the Meta Hacker Cup 2022 Round 2 and advanced to Round 3 (preceding the final one). I do not hope that I will go to the finals, but for me participating in Round 3 is already as cool as in a final one!

A recording of my participation can be viewed here.

Today I participated in Codeforces Round 819 (Div. 1 + Div. 2) and Grimoire of Code Annual Contest 2022. At first glance, this was really a nice contest, and even though some problems were a bit too technical, they did contain some certain ideas (and as to whether these ideas were cool and beautiful, I guess there's no accounting for taste). However, the tests in the harder problems weren't strong enough. For example,

• I easily uphacked nikgaevoy's solution 171150224 of 1726F - Late For Work (submissions are not allowed), where he printed negative numbers on tests as little as with $$$n=2$$$; (btw, congrats nikgaevoy on becoming an IGM!)

• heno239 uphacked turmax's solution 171126442 of 1726G - A Certain Magical Party with also a tiny test; (btw, congrats turmax on becoming an LGM!)

Nevertheless, I screencast the solving process (with my struggling to solve 1726F - Late For Work (submissions are not allowed)) and explanation of problems A–F, and I am now uploading it to YouTube, the video should appear here in several hours. Please leave your feedback (and other cases of high- or low-quality testing in this contest) in the comments!

UPD: While I was sleeping, two news have happened:

1. The video uploaded successfully.

2. The round became unrated because of the problem F, from which I suffered a lot during the contest. (By the way, the suffering had nothing to do with the quality of the tests in this problem or with this issue, I just made stupid bugs). You may read this and this blog to get to know the incident.

I got to the 41^st place in Codeforces Round 814 (Div. 1), which quite surprised me because my last several contests were also pretty lucky, not to say in this contest I was extremely slow in solving the problem A. Still I followed the tenet from the never_giveup's handle and finished the contest, it happened to be not that bad. Moreover, I beat my personal best of rating. I screencast and explained 1718A2 - Burenka and Traditions (hard version), 1718B - Fibonacci Strings, 1718C - Tonya and Burenka-179 and partly 1718D - Permutation for Burenka from this contest here: https://youtu.be/6iaSJikYZ-o

Feel free to watch and leave your invaluable feedback!

Since there were not that many Div. 1 rounds last several days, I decided to compete in a Div. 2 round. This time my participation was quite poor, but still I solved and explained some of the problems in front of a camera, so I hope that my video will be useful for my adorable viewers: https://youtu.be/ZF42Y5cQhf4

As with my previous video, any sort of feedback is welcome in the comments.

Recently I started screencasting my contests, there are already several videos on my channel. They all are in Russian because I ponder in Russian.

Today, as an experiment, I decided to screencast CodeTON Round 2 and comment my actions in English. Yes, my reasoning is often fragmentary there (because under the pressure of time I cannot spend much time explaining a lot of things rather than start coding). Still, since I finished 24^th I expect it to be rather entertaining content, thus I invite you to watch the process: https://youtu.be/ZK8vVVhoQXI

Since I am very new to exploring this niche, any sort of advice of improving the quality of my videos is highly welcome here in the comments, on the Youtube, or in my PM.

Several days ago I published a table with first people to reach certain ratings. It featured only ratings above 1500, and adamant advised to do the same, but on achieving ratings below 1500. I found it quite interesting, and, after several days of collecting data about participations of 447911 Codeforces users, I finally made this table.

Several days ago I published a table with first people to reach certain ratings. It was a bit raw because, firstly, it was based on top 20000 Codeforces users by rating, and, secondly, because it only gave information about ratings divisible by 50. Now I have prepared a table that is of more complex design, but both issues are resolved. Good luck understanding what is going on in it.