In the latest Educational Round, there was a problem E that was split into two subproblems. After solving E1, I realized that my solution can solve E2. This made me curious about the participants who hadn't solved E2 yet, and what their idea was. After looking at a few submissions, I noticed their core idea was identical to mine. I even resubmitted four of their solutions for E2—and three of them got Accepted, even though those participants hadn't even attempted E2. Looking further, I found the exact same code used by this participant and another user, though I forgot the handle of the other one. My sample size was taken from participants ranked between 200th and 400th on the leaderboard.

In short, I wanted to point out that many gray and green participants submitted E1 but didn't submit E2, even though their code passes all the tests for E2.

During the last APIO in Uzbekistan, something surreal happened. Some participants brought a diesel engine to the olympiad.
footage recorded on video:

Click to watch the video

How often do you read blogs?

Codeforces Round Announcement/Editorial

The most common reminder that here you can not only read blogs, but also solve/upsolve problems.

Atcoder Contest Announcement

Try solving the problems on another vjudge.

Please ban this cheaters

Law enforcement officers, look at other people codes and check whether LLM wrote the code.

Rule about third-party... Author: MikeMirzayanov

Have you seen how many comments there are?

I just started learning competitive programming.

Newbies who are just learning to code share how they solved problems and ask for advice on how to move forward.

I solved this problem in a round by using another idea.

Either geniuses who found a simpler solution, or those who did not understand the authors solution and wrote it their own way.

Challange to reach a lot of rating

He set a goal for himself that he wants to reach, and he is posting his progress (GL).

How solve this problem?

Couldn't find/understand the editorial and are asking the community for help.

SCIOI teams(Super Cool International Olympiad in Informatics)

They are collecting information about teams for the next international Olympiad.

Algorithm for problem solving

They describe another algorithm that is either found in one problem from the entire archive, or a very popular one that has been explained everywhere possible.

Codeforces crash

Codeforces crashed again, and the stream is full of blogs about "Why codeforces crashed" or "my submission is already 30 minutes in queue".

holiday greetings

Although there are not many holidays, holiday greetings keep coming consistently.

Another shitposter

Another lowrated guy couldnt figure out how to stand out from the crowd, so he started farming -100 contribution.

AI slop

They often combine an explanation of the algorithm, tips, and how to reach the red color(while they are the green). (Do you want to change this text so that it looks less like the text generated by LLM?)

When rollback

Many rounds have passed, but the rollback hasnt happened yet. (Good luck to those who are just a little short of reaching the next color.)

Link to tierlist

You can add your defines in the comments, I will add interesting to the tierlist.

A few hours ago, the hacking phase for the round (Div. 3) ended and the system testing began. I wanted to check how many solutions failed the system tests, and I saw a huge number of TLEs on problem C. After looking at several solutions, I realized that they all had one thing in common — unordered_map.
I think many people know that unordered_map (hereafter UM) can work in both $$$O(1)$$$ and $$$O(n)$$$ time. Because of this, some people found a test case where UM runs in $$$O(n)$$$, which makes the overall complexity $$$O(n^2)$$$.
It got me wondering why people massively use UM when a regular map passes within the time limits. I asked ChatGPT to solve this problem, and it gave me a solution using UM.

#include <bits/stdc++.h>
using namespace std;
using ll = long long;

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t;
    if(!(cin >> t)) return 0;
    while(t--) {
        int n;
        ll k;
        cin >> n >> k;
        vector<ll> S(n), T(n);
        for(int i=0;i<n;i++) cin >> S[i];
        for(int i=0;i<n;i++) cin >> T[i];

        unordered_map<ll,int> cntS, cntT;
        cntS.reserve(n*2);
        cntT.reserve(n*2);

        auto rep = [&](ll x)->ll {
            ll r = x % k;
            if(r == 0) return 0;
            if (k % 2 == 0 && 2*r == k) return r; // специальный случай при k чётном
            return min(r, k - r);
        };

        for(ll x: S) cntS[rep(x)]++;
        for(ll x: T) cntT[rep(x)]++;

        if(cntS == cntT) cout << "YES\n";
        else cout << "NO\n";
    }
    return 0;
}

On the one hand, it’s kind of funny that people who copied from ChatGPT (or another LLM) got their solutions rejected.
On the other hand, there are people who wrote the code themselves but decided to use UM instead of map (although I think that’s their own fault because they could have just used a regular map).

Everyone knows that there are quite a few cheaters on rating rounds, but there were a lot of cheaters on the last round.
In the top 20 official users there are at least 10 users with a rating of less than 1200. This is a lot and the situation is terrible. Codeforces need a new anti-cheat system.
But I also want to say that competive programming (and not only, I think this applies to all industries) after the development and improvement of AI will move into a new era.