In the last round (Codeforces Round 1007 (Div. 2)) I have noticed multiple people submitting similar solutions, The cheaters just copied a solution for 2071D1 - Бесконечная последовательность (простая версия), After some search (I really need to get a life) I was able to find the solution on you that they copied from:

#include <bits/stdc++.h>
using namespace std;
 
int f(long long m, long long n, int B, const vector<int>& p) {
    if (m <= n) return p[(int)m];
    return (m & 1LL) ? B : B ^ f(m / 2, n, B, p);
}
 
int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);
    
    int t;
    cin >> t;
    
    while (t--) {
        long long l, r;
        int n;
        cin >> n >> l >> r;
        
        vector<int> a(n + 1);
        for (int i = 1; i <= n; i++) {
            cin >> a[i];
        }
 
        if (l <= n) {
            cout << a[(int)l] << "\n";
            continue;
        }
 
        vector<int> p(n + 1);
        p[0] = 0;
        for (int i = 1; i <= n; i++) {
            p[i] = p[i - 1] ^ a[i];
        }
 
        int fn = p[n];
        int B = (n & 1) ? fn : fn ^ p[n / 2];
        long long m = l / 2;
        
        cout << f(m, n, B, p) << "\n";
    }
    
    return 0;
}

The two important line here are these:

cout << a[(int)l] << "\n";

and

if (m <= n) return p[(int)m];

There is no real reason for someone to cast an to index from long long to int in the middle of the contest, but, most cheaters also have this in their code (some even cast to ll for some reason)

Of course people who cheated must also have the same approach, but this eliminates the possibility that they may have came with the same solution as the one leaked on youtube.

Here are some cheaters from the top 20:

1. 308321301

2. 308354334

3. 308319240

4. 308319309

5. 308322024 (He is using Java, but still it's hard to not be copied)

I was planning to do the entire first page, but didn't expect to find that much cheaters, doing the entire first page would take forever..

Note that these are the submissions that copied the type cast, maybe there are still some cheaters didn't do so, the type cast indicates that the original solution that these was copied from was written in a language like Java.

The fact that a lot of people were able to cheat their way to the top 20 of a div 2 and have a performance of a red coder is scary.

I think IP ban should be implemented into codeforces to reduce cheating, because this is becoming a real issue.

Edit: This user mehukhal was streaming during the contest and used some LLM to slightly modify solutions, a lot of submissions are too similar to those LLM modified solutions.

After checking the submissions the first one to do this was this one: 308309430.