Some background —

I use Python for CP and some benefits of using Python are clear and concise syntax, tons of in-built function, dynamic typing, FP-like operations (map, filter, accumulate etc.), list comprehensions, bool-to-int conversions and so on. These features make code-golfing very fun with Python. I discovered jahnvisahni98 in the solutions section of some problem few weeks ago (you can sort solutions by their size). If I find some user frequenting the section, I usually befriend them on Codeforces and even send a message saying I appreciate them. But this case was different. The solution's logic was still long, but the syntax had been shortened by giving a tab space of 1 character. I looked through some of her other solutions and she had a different code style in all of them. Somewhere she had formatted code with long variable names while at other places she had short undecipherable variable names with very poor formatting. This was still not a strong enough evidence.

Fast forward to today, her submissions on 2078C - Breach of Faith speak volumes. Within 2 minutes of submitting problem B, she submitted an O(n^2) solution to C 309795444 that did not even pass sample testcase. Then 8 minutes later, a completely different approach and still fails to pass sample testcase 309803089. 1 minute later, a similar approach but fails sample testcase 309803977. 10 minutes later, she is back with a new approach but this time the code is almost undecipherable 309811178. Fails on the sample testcase regardless.

One minute later, she has already solved D 309811985.

Now back to C. She switches her coding style from undecipherable to decipherable again and submits another testcase 1 failure 309816146 7 minutes later. 1 minute later, she submits another test case 1 failure 309816146.

Now comes the interesting part. 6 minutes later, she submits a poorly formatted solution to 2078F - Binary Subsequence Value Sum which passes all test cases. I do have an explanation for these strange code style change.

She ends her day with another submission on C 4 minutes later, which you can guess, failed on sample testcase 309822692.

My Opinion/Explanation —

This is a classic case of cheating with the help of LLMs. The frequent changes in code style can be explained by the change in LLMs. The poorly formatted short variable name code is a result of her prompting the LLM to make the code look messy and asking it to use shorter variable names with no comments. I will let MikeMirzayanov and the Codeforces community be the judge in this case. I hold no personal grudges. I don't even know her. I found clear evidence of cheating from an account and decided to report it.