A friend of mine told me about a suspected cheater, batats, so I decided to check his submissions myself. Here are a few reasons why I suspect that batats may have cheated in some recent contests.

1. Rapid Rating Increase

He registered on Codeforces 5 years ago and stayed at newbie level for a very long time, with his rating never exceeding 1200. However, during the last 2 months, his rating suddenly skyrocketed.

He went from 1107 rating after Educational Codeforces Round 188 to 2107 rating after Codeforces Round 1099 (where he achieved rank 2) in only 6 contests.

Of course, rapid improvement is not impossible. Some people improve very quickly. However, after looking at his submission history, the jump feels suspicious. Earlier, he was solving around 3 out of 7 problems in Div. 2 contests, but only 2 months later, he suddenly solved 6 out of 6 problems in a much stronger performance.

Maybe it is legitimate, but the improvement speed is unusual enough to raise questions.

2. Sudden Changes in Coding Style

Another thing I noticed was the inconsistency in his coding style.

In the first 4 contests among these recent rounds, his code looked very cluttered:

• compact formatting,
• very few spaces,
• dense implementation style.

Then, in the 5th contest, he suddenly switched to a completely different style. While changing templates is perfectly normal, the way he wrote code inside main() and other functions also changed noticeably:

• cleaner formatting,
• much more spacing,
• overall more readable structure.

But in the 6th contest, although he still used the new template, he immediately went back to his old cluttered coding habit.

That sudden one-contest-only change feels strange. Usually, coding style is one of the most consistent habits for competitive programmers.

Again, this is only suspicion, not proof. There may be completely legitimate explanations for all of this. If batats wants to clarify anything, he (or she) is welcome to respond in the comments.