Today I got this message:
When looking at the solutions of the listed participants on the problem 1951B I saw that all these solutions completely (or with a change of variables) same as mine, so it's not just a coincidence, solutions copied from mine. Since I didn't give my solution to anyone, and didn't keep the code publicly available, this could only happen if one of the participants blocked this task, copied my code, and sent it to the others.
Indeed, it turns out that in my room only one participant blocked task B — _Untrackable_(the nickname speaks for itself). He blocked this task at 1:44, and if you look at the submissions of participants from the list, you can see that many of them earlier sent code for this task that was completely different from mine (some even in other languages!), but all of them at approximately 1:55 (after he blocked this task), sent almost exactly my code.
This method of cheating at contests allows the person who sends solutions to everyone to remain unpunished, and all the punishment goes to another honest participant.
Please look at this problem, MikeMirzayanov.