https://youtu.be/ylxfBRPWLtw

Ugh, it was a hard contest. I spent a huge amount of time on both 2222D - Permutation Construction and 2222F - Building Tree, but couldn't crack them.

link

Personally I felt like my participation in Nebius Round 2 (Codeforces Round 1088, Div. 1 + Div. 2) was acceptable, but this perception contrasted sharply with my objective standing in the standings. Either I'm that rusty after six months of idleness, or probably my rank might have been affected by some mass effects. What could they be, that is the question!

Overall, the problems were really nice. I felt like 2211F - Learning Binary Search was easier than 2211D - AND-array, and also in last half an hour, unfortunately, I chose to aim for 2211G - Rational Bubble Sort instead of 2211E - Minimum Path Cover (to try and win duels against isaf27 and turmax), but I lost the race and the duels. A subsequent investigation showed that I had excellent chances of solving problem 2211E - Minimum Path Cover, if only I’d given it a try. Maybe such strategic mistakes (along with lack of consistent training) are what's keeping me from nutelling.

https://youtu.be/n6Zvg_dLOz4 — will upload in half an hour.

I liked this round! However, tons of submissions in 2147G - Модульная тетрация are kinda sus...

https://youtu.be/oXjG3uZYXFc

Will upload in approximately an hour.

My experience was seriously damaged by the wrong formulation of B, so personally I'm glad that the round got unrated.

I managed to take 2413th place, which is an anti-record for my entire programming career. My thoughts on G were not entirely wrong, and a small miscalculation affected my solving process; and also, even if I had managed to solve G, it would have been so late that the penalty simply wouldn't have been worth it.

Learn to not do like I did! https://youtu.be/C5UOOzLjwrk

Nothing to say, to be honest. Please watch if you're interested in that how problems A–F1 are solved: https://youtu.be/OtiLL5bJ76Y (the video is already on the channel, high quality can take some time).

I missed participating in Codeforces rounds a lot, so i took a shot in Neowise Labs Contest 1 (Codeforces Round 1018, Div. 1 + Div. 2). It was enjoyable! I hope I can share some delight with you by giving a screencast, as well as a quick editorial of problems A–E, G. I still have no idea how 2096F - Wonderful Impostors can be possibly solved, though :D

The video should upload in several minutes: https://youtu.be/OqbMyIavR5Q

I continue exploring the new Blitz format! This time I competed with isaf27: https://youtu.be/JsyUxgqRzbE.

Since the format of Codeforces Blitz Cup 2025 is quite novel here, a possibility for warmup duels was introduced: both to train for this specific format and to warm-up prior to the real tournament duels.

Yesterday I played one such duel against budalnik: https://youtu.be/bIzLZ1R5Gmk. The screencast of that will upload in around an hour and a half.

MikeMirzayanov announced a series of duels in March. These duels are already taking place, and I played one such duel against SendThemToHell. Please watch https://youtu.be/TEjQRvjzE_Q if you're interested how it goes!

Happy Valentine's Day!

I am pleased to invite you to participate in Stage 30 of the 3rd Season of Universal Cup. The contest is five hours long and will take place tomorrow in eight time windows, the first one starting on Saturday, February 15, 2025 at 08:00^[UTC+8], and the last one starting on Sunday, February 16, 2025 at 02:00^[UTC+8]. It will feature the problemset of SPb SU Contest from 48th Petrozavodsk Programming Camp that took place on Tuesday, February 4, 2025 at 10:00^[UTC+3].

The contest is authored by a team from St. Petersburg State University: Gassa, Kaban-5, naagi, nikgaevoy, orz and tranquility. We hope you'll enjoy the problems!

About Universal Cup

The Universal Cup is a contest series for competitive programming teams. The stages are various camp stages, ICPC regionals, local contests and the like. This scheme gives participants fresh, diverse and quality contests to train and compete, at the same time allowing local contest authors to share their work with the world.

Announcement of the 3rd Season: https://mirror.codeforces.com/blog/entry/129908.

Registration is possible before every stage. If your team participated in at least three stages of the previous season, it is registered already.

Rules and time windows for participation.

After quite a pause, I participated in recent Codeforces Global Round 27. After solving A–E in some admissible time but unfortunately struggling for some time with 2035F - Tree Operations, I chose to take the risk and solve the last problem, 2035H - Peak Productivity Forces for which fortunately there was quite much time to sit and figure everything out. Soon it became obvious that it was just a constructive problem without any horrible data structures; one just needs to carefully sort out all cases and not bug a lot. I was very happy to perform it — in these latter days I pretty often feel frustrated that I solve all easy problems (gentleman's set, so to say) but stop at one which is a bit harder, and I seldom am able to solve this one problem (which is usually enough to get a very cool place). Well, today is a nice day!

I explained the problems that I solved right after the screencast itself, you are welcome to watch it: https://youtu.be/WdkTDjb1knw.

UPD: the sound was too quiet, I tried amplifying it: https://youtu.be/jRKJbNO-3kg

Hello!

Recently I published two posts one, two featuring users that were first, second, etc. to reach some rating value.

The reason I was able to create these posts was that preliminarily I downloaded all users' rating change history via Codeforces API. It took some time, but now, when the job is done, I have more than 700000 files, in each one of them a json is stored which represents one user's full rating change history (as an array, and each change consists of the old rating, the new rating, contest name, link and date, taken place and probably something else). I feel a slight feeling of something left unsaid/undone. Probably, because, even though I built that tables, I did not use 99.9% information at all. That simply means that more can be done now!

Could you please suggest some ways to aggregate this data and get some entertaining results? For instance,

• get the rating list sorted by maximum rating rather than the actual rating;
• get the maximum amount of rating gained by someone in two, three, four, five, etc. consecutive contests; or in two, three, four, five first contests taken by the user (though I dislike the idea with the word first as it encourages people to register twin accounts);
• rank all users by the number of times they defeated tourist;
• as a development of the previous bullet, for each user their tourist number can be calculated (it is defined similarly to Erdős number: tourist is the only person with zero tourist number, and for all positive integers $$$n$$$ people with tourist number equal to $$$n$$$ are defined as ones who defeated a person with $$$n-1$$$ tourist number but never defeated anyone with a smaller tourist number);
• rank all users by the number of rated contests (or rated Div. 1 contests, or rated Div.1 + Div.2 contests) they participated in;
• rank all users by the numbers of contests which they won / were second / were third;
• rank all users by the number of contests they participated in (ruban?) / by minus the number of contests they skipped since their first participation;
• rank all users by the difference of their maximum and the minimum rating / by the maximum difference of some reached rating and some previously reached rating / by the number of colors they have been colored in since their fifth contest (although this encourages stalactites and stalagmites);
• rank all users by their volatility (e.g. how many times the sign of their rating change differed from the previous one, or how many times they changed their title or color, or what is the standard deviation of their rating, or what is the sum of absolute values of their rating changes, etc.), or find most stable users who participate a lot but still have a very horizontal graph (or a very horizontal segment);
• find the highest place in which there happened to be a draw in a contest;
• rank all users by the smallest place they reached;
• rank all users by the smallest place which they reached and got a negative delta;
• rank all grandmasters by the number (or minus the number, to discourage twin account creation and encourage hard work) of contests it took them to reach their title;
• rank all users with the substring orz in their handles;
• and much more!

Please share your ideas in the comments and upvote/downvote others' ideas, and I'll try to implement the nicest ones of them!

Note. This is an updated version of this post. If you like this style more, please tell me in the comments.

Since tourist's breakthrough, I've received a lot of requests to update my old posts with rating achievements. However, I wasn't able to do it immediately since my method of doing it requires to download the rating change history of every user, which, in turn, requires to perform several hundred thousand requests to Codeforces, about which the website (and Cloudflare) is not happy. It took more that three days, but finally the job is done!

Below are two tables. The first one is the greatest (by absolute value) negative rating changes. The second one is the first users ever to reach some rating value.

Note. This is an updated version of this post. If you like this style more, please tell me in the comments.

Since tourist's breakthrough, I've received a lot of requests to update my old posts with rating achievements. However, I wasn't able to do it immediately since my method of doing it requires to download the rating change history of every user, which, in turn, requires to perform several hundred thousand requests to Codeforces, about which the website (and Cloudflare) is not happy. It took more that three days, but finally the job is done!

Below are two tables. The first one is the greatest positive rating changes. The second one is the first users ever to reach some rating value.

I solved problems A–D, but I was quite slow, also I had two incorrect submissions for problem A, so my rating delta was -21.

If you want to watch my screencast and editorial, it will appear (UPD: has appeared) behind this link in several minutes: https://youtu.be/NuyV1LIMX3E; or in this box:

And, of course, my warmest congratulations to tourist on reaching 4000 rating points milestone!

The video is already uploaded: https://youtu.be/ItdpgiFG-Bw

The video is already uploaded: https://www.youtube.com/watch?v=9MXalADEPZk

I solved A–F from Codeforces Global Round 26. Unfortunately, I had experienced issues with judgement system, so the participation was a bit spoiled for me, and it was made unrated. Nevertheless, the problems were quite fun, hope I'll become much faster one day!

Please watch! https://youtu.be/4B3g4NLdbuA

I've solved and explained all five problems of Codeforces Round 948 (Div. 2), the video will appear in about an hour.

UPD: the video is available.

I have recorded a screencast & editorial for Codeforces Round 947 (Div. 1 + Div. 2). It will upload on https://youtu.be/DrBmSO86xUQ in an hour or two.

UPD: the video is uploaded.

Tomorrow (in 12 hours) is the main day of my first ICPC WF! The preparation is over. We are not worried, but, unfortunately, after all the rounds of Ptz, UCup, previous years' ICPCps, it is clear to us that we will not win a medal without any luck. Please cheer for us and wish us luck! For two of our team, including me, this is our last attempt at the finals.

You should be able to find us tomorrow somewhere on https://www.youtube.com/@ICPCLive/, we will be 47^th WF St. Petersburg State University team.

Good evening everyone!

TL;DR: I am in Luxor preparing for ICPC WF and making some photos, and also I was offered to (and I will) give an interview to Shayan, please send your questions.

I really liked today's Codeforces Global Round 25! I got a pretty nice positive delta, although, unfortunately, I failed to settle down all the nasty conditional probabilistic formulae in 1951G - Clacking Balls and solved one problem less than I could have.

I uploaded my screencast and editorial on YouTube: https://www.youtube.com/watch?v=4-8kp8B2Dig. Surprisingly, the video is still processing, so it is still impossible to watch it. But it should become available in several minutes.

UPD: the video is available.

UPDUPD: the video is available in high resolution.

Today I participated in a pretty nice CodeTON Round 8 (Div. 1 + Div. 2, Rated, Prizes!) and recorded a pretty nice Screencast and Editorial of problems A–G. You are welcome to watch it!

UPD: now the video is in high quality.