Codeforces Round 1062 (Div. 4) Was full of cheaters, I thought they are getting removed in the rollback, but here was the rollback yesterday and the cheaters that were on the top of the standings are still there, so here is the list of cheaters I was able to collect before Codeforces stopped me from opening any more submissions, I'm may not say exactly some of the evidence as it may help them avoid getting caught in the future, but anyone can easily see it by browsing submission, note that I'll only write the problems I checked in the problem field, they may have cheated in some other problems.

Codeforces should really improve the plag check, a lot of these cheaters didn't even make any effort to hide that they cheated and they still didn't get caught, also a lot of submissions are identical, the Plag checker should at least catch those....

21 out of the top 27 are cheaters, that's about 75%, which is not a good percentage of cheaters to have on the top of the standings.

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.