On the Global Round 31, user Su_Zipei has just used AI to make it to the top 20 of the contest.

Indeed, a smart contestant would not use overtly suspicious AI-generated code; those grey participants who rapidly solve the first six or seven problems in a competition can easily be identified as having used AI. A better approach is to obfuscate and polish the code provided by AI, or even rewrite it based on the AI's logic——for contestants with enough coding experience, this is quite straightforward. Clearly, compared to a 1200-rated player using AI to reach 1800, a 2400-rated player finds it easier to use AI to reach 3000.

Still, we can find some evidence that is not so convincing. For those people who solve problem H1 fast enough, Kevin114514 uses 36 minutes, tourist uses 42 minutes, ecnerwala uses 32 minutes, while other pariticipants solves it even longer(~1h). However, Su_Zipei only solve it in 19 minutes, which is really, really fast.

Another issue that requires attention is this code uses captital letter "MOD" for modulo number. This is a rather rare habit because you need to type a lot of "MOD", and holding down the shift key each time can be very annoying. In contrast, most AI-generated code uses uppercase "MOD". For comparison, this code and this code from the same contestant use p and mod as the modulus, respectively.

Of course, this evidence is not particularly strong. In fact, unless the user is extremely careless, it is difficult to find truly conclusive proof of AI usage. The reason I am writing this post is that I know this user offline and am clearly aware that he has previously used AI to participate in competitions. Given that AI is now sufficiently advanced, it is challenging to effectively ban its use in online contests. However, I hope to discourage situations where individuals rely entirely on "piloting" AI to achieve extremely high rankings. This requires joint efforts from both the community and the participants.