Hello, CodeForces.

As I can't find any discussion thread in AtCoder, and the announcements of AtCoder contests are also posted here, I decided to post this blog in CodeForces.

Last time (ABC355), I reported a suspicious participant toyuzuko who solved problem ABCD in 51 seconds. They also did the similar thing in ABC354.

This time (ABC356), there are much more suspicious participants.

The average first-AC time (in seconds) of ABC347~ABC353 is in the following table:

Contest | A | B | C | D | E | F | G |
---|---|---|---|---|---|---|---|

ABC347 | 21 | 45 | 93 | 244 | 177 | 300 | 824 |

ABC348 | 15 | 37 | 72 | 302 | 236 | 495 | 430 |

ABC349 | 23 | 67 | 54 | 116 | 598 | 139 | 634 |

ABC350 | 26 | 47 | 102 | 74 | 240 | 489 | 335 |

ABC351 | 22 | 23 | 106 | 352 | 199 | 122 | 902 |

ABC352 | 27 | 43 | 49 | 90 | 196 | 989 | 188 |

ABC353 | 24 | 79 | 172 | 88 | 206 | 1161 | 313 |

(minimum) | 15 | 23 | 49 | 74 | 177 | 122 | 188 |

(prefix sum) | 15 | 38 | 87 | 161 | 338 | 460 | 648 |

Note that to get first-AC in a problem doesn't require you to solve all the problems before it. You can just skip to the problem you want to get first-AC and manage to solve it at once. So, the least reasonable time to solve a subset of problems is at least the sum of the first-ACs.

To make sure there are fewer exceptions, I will call all the participants who solved any subset of problems faster than the minimum expected time "suspicious".

Now, let's take a look at (some of) the suspicious participants who solved at least 4 problems at last:

- kyon2326 solved ABCD in 25 seconds.
- toyuzuko solved ABCD in 28 seconds.
- Harui solved ABD in 24 seconds.
- udon1206 solved ABC in 40 seconds.

Some other participants seem to be suspicious, too. They solved a subset of problems just 10 seconds slower than the sum of the minimum first-AC time in the above table. I think it's impossible to have all the easy problems in a single round, but I didn't list them here, just to make sure there are fewer exceptions.

I guess they probably used some AI to generate the code for them after seeing what happened in ABC355. If my guess is true, I'm impressed with the ability of AI. I'm also worried that more and more people will use AI to generate the code and solve easy problems in the contest. If everyone can solve ABCD by simply copy-pasting AI's code, what's the point of having AtCoder Beginner Contests? Why not just delete ABCD and add some new problems to make an AtCoder Regular Contest?

You can leave your opinion in the comments.