Cheater Got Talent Episode 2: bismispis

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Welcome to the Cheater Got Talent's second episode! It has been 10 days since the last episode; I'm sorry because I've been busy lately. So, here we go—episode 2 of Cheater Got Talent!

And today's guest: a Master whose peak rating is Grandmaster: bismispis. Also, a big shoutout to Christine-'s community for finding this cheater.

Let's take a look at bismispis's contests:

His (or her?) contests look normal, except for the 6th and 7th contests (believe me, this is a coincidence...), where he placed first and where he solved nothing.

Let's take a closer look at his 6th contest:

At first glance, his code seems normal. Although he has long variable names in F (best_leaf, max_cand, etc.), his submissions for A, B, C, D, and E seem to be legitimate. Maybe he solved A–E by himself, then used AI for F. This is just a theory.

There isn't enough evidence to conclude that he cheated, so let's continue with his 7th contest.

(Tip for finding cheaters: If the person you're investigating participated in a contest and solved 0 problems, it's likely that their submissions were skipped.)

Just as we expected, his entire contest was skipped. But, to be honest, his skipped submissions look fine. For example:

His code for H

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

typedef long long ll;
const ll MOD = 998244353;

int main() {
    ll t;
    cin >> t;
    
    while (t--) {
        ll n;
        cin >> n;
        string s;
        cin >> s;
        
        vector<ll> p(n + 2, 0);
        vector<ll> q(n + 2, 0);
        
        for (ll i = 0; i < n; i++) {
            p[i + 1] = p[i];
            q[i + 1] = q[i];
            if (s[i] == '1') {
                p[i + 1]++;
            }
            if (s[i] == '?') {
                q[i + 1]++;
            }
        }
        p[n + 1] = p[n];
        q[n + 1] = q[n];
        
        auto check = [&](ll l, ll r) {
            if (l >= r - 1) {
                return true;
            }
            ll qs = q[r - 1] - q[l];
            ll ones = p[r - 1] - p[l];
            if (qs > 0) {
                return true;
            }
            if (ones % 2 == 0) {
                return true;
            }
            return false;
        };
        
        vector<vector<vector<int>>> nxt(n + 2, vector<vector<int>>(2, vector<int>(2, n + 1)));
        
        for (ll i = 0; i <= n; i++) {
            for (ll c = 0; c < 2; c++) {
                char tar = '0';
                if (c == 1) {
                    tar = '1';
                }
                for (ll j = i + 1; j <= n; j++) {
                    if (s[j - 1] == tar || s[j - 1] == '?') {
                        if (check(i, j)) {
                            ll par = p[j] % 2;
                            if (nxt[i][c][par] == n + 1) {
                                nxt[i][c][par] = j;
                            }
                        }
                    }
                }
            }
        }
        
        ll ans = 0;
        int lim = n + 2;
        vector<int> dp(lim * lim, 0);
        dp[n + 1] = 1;
        
        for (ll m = 0; m <= n + 1; m++) {
            auto go = [&](ll u, ll v) {
                int val = dp[u * lim + v];
                if (val == 0) {
                    return;
                }
                
                bool acc = false;
                if (u <= n) {
                    if (check(u, n + 1)) {
                        acc = true;
                    }
                }
                if (v <= n) {
                    if (check(v, n + 1)) {
                        acc = true;
                    }
                }
                
                if (acc) {
                    ans = (ans + val) % MOD;
                }
                
                for (ll c = 0; c < 2; c++) {
                    ll nu = n + 1;
                    ll nv = n + 1;
                    
                    if (u <= n) {
                        if (nxt[u][c][0] < nu) {
                            nu = nxt[u][c][0];
                        }
                        if (nxt[u][c][1] < nv) {
                            nv = nxt[u][c][1];
                        }
                    }
                    if (v <= n) {
                        if (nxt[v][c][0] < nu) {
                            nu = nxt[v][c][0];
                        }
                        if (nxt[v][c][1] < nv) {
                            nv = nxt[v][c][1];
                        }
                    }
                    
                    if (nu <= n || nv <= n) {
                        dp[nu * lim + nv] = (dp[nu * lim + nv] + val) % MOD;
                    }
                }
            };
            
            for (ll v = m; v <= n + 1; v++) {
                go(m, v);
            }
            for (ll u = m + 1; u <= n + 1; u++) {
                go(u, m);
            }
        }
        
        cout << ans << endl;
    }
    
    return 0;
}

His code for F

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

typedef long long ll;

const int MAXN = 300000;
int carr[MAXN];
ll warr[MAXN];
ll smarr[MAXN];
ll arrg[20];

int main() {
    ll t;
    cin >> t;
    
    while (t--) {
        ll n;
        ll k;
        cin >> n >> k;
        
        vector<ll> a(n);
        ll sum = 0;
        
        for (ll i = 0; i < n; i++) {
            cin >> a[i];
            sum += a[i];
        }
        
        sort(a.rbegin(), a.rend());
        
        ll ans = 0;
        
        for (ll i = 0; i < n; i++) {
            ll x = a[i];
            ll l = 0;
            
            if (ans + 1 - x > 0) {
                l = ans + 1 - x;
            }
            
            ll r = (sum - x) / k;
            
            if (l > r) {
                continue;
            }
            
            ll sz = n - 1;
            ll mx = 1LL << sz;
            int idx = 0;
            
            for (ll j = 0; j < n; j++) {
                if (i == j) {
                    continue;
                }
                arrg[idx] = a[j];
                idx++;
            }
            
            smarr[0] = 0;
            for (ll mask = 1; mask < mx; mask++) {
                ll bit = mask & -mask;
                int j = __builtin_ctzll(bit);
                smarr[mask] = smarr[mask ^ bit] + arrg[j];
            }
            
            ll best = -1;
            
            while (l <= r) {
                ll mid = l + (r - l) / 2;
                bool ok = false;
                
                if (mid == 0) {
                    ok = true;
                } else {
                    for (ll mask = 0; mask < mx; mask++) {
                        carr[mask] = -1;
                        warr[mask] = 0;
                    }
                    carr[0] = 0;
                    
                    for (ll mask = 0; mask < mx; mask++) {
                        int cnt = carr[mask];
                        if (cnt == -1) {
                            continue;
                        }
                        
                        ll cw = warr[mask];
                        ll cur = smarr[mask] - cw;
                        ll rem = (~mask) & (mx - 1);
                        
                        while (rem > 0) {
                            ll bit = rem & -rem;
                            rem = rem ^ bit;
                            int j = __builtin_ctzll(bit);
                            
                            ll nmask = mask | bit;
                            int ncnt = cnt;
                            ll nw = cw;
                            
                            if (cur + arrg[j] >= mid) {
                                ncnt++;
                                nw = smarr[nmask];
                            }
                            
                            if (ncnt > carr[nmask]) {
                                carr[nmask] = ncnt;
                                warr[nmask] = nw;
                            } else if (ncnt == carr[nmask]) {
                                if (nw < warr[nmask]) {
                                    warr[nmask] = nw;
                                }
                            }
                        }
                    }
                    if (carr[mx - 1] >= k) {
                        ok = true;
                    }
                }
                
                if (ok) {
                    best = mid;
                    l = mid + 1;
                } else {
                    r = mid - 1;
                }
            }
            
            if (best != -1) {
                ll curval = best + x;
                if (curval > ans) {
                    ans = curval;
                }
            }
        }
        
        cout << ans << endl;
    }
    
    return 0;
}

Maybe his submissions were skipped because his code was similar to someone else's. However, I'm still convinced that he used AI, because:

If you take an even closer look, you'll notice that he submitted G five times, none of which received AC. Let's take a look at his first submission. It seems normal, except for the commented-out lines of code. Just 3 minutes later, at 02:39, he resubmitted it with many changes. You can find his second submission here. Let me remind you that this is a 3-hour contest. He had just solved ABCDEFH, so if he wanted to have a GM-level performance, he needed to solve more problems quickly. That's when he panicked.

Exactly 60 seconds later, he submitted I (at 02:40), which got TLE11. However, if I were him, I would argue that I had already written the solutions for G and I and simply submitted both at once.

As I said above, I think the second argument is weak because he can easily defend himself. That's why the last three submissions for G are important. He submitted the third version of G at 02:43 (3 minutes after his submission for I). His new code has only a few minor changes compared to the one he submitted 6 minutes earlier. Two minutes after receiving RTE3 on the third submission, he submitted the fourth one. This submission contains even fewer changes (you can check it yourself). A GM wouldn't do something like this because they would know that resubmitting code that is already wrong would only result in a 50-point penalty. In his final submission, he reverted the changes he made in the third and fourth submissions and also added a few comments. Someone who was panicking would never do this.

That's why I'm convinced that he used AI.

To be honest, I think the arguments I used in this case are much weaker than the ones I used in the first episode. Still, I believe that bismispis cheated.

So that's the end of the Cheater Got Talent's second episode! Thank you for reading, and I wish you all good luck in the upcoming Div. 1 + 2 contests.

P.S. I forgot to mention this earlier: when he submitted H at 01:13 (which got TLE11), he submitted another version at 01:24 (which was skipped during the main tests), and it differs significantly from the previous one.

Комментарии (24)

Написать комментарий?

CheaterGotTalent

3 месяца назад, скрыть # |

-19

btw, I used AI to fix my grammar, so this blog might looks like it was written by AI

→ Ответить

Prototype1510

3 месяца назад, скрыть # ^ |

u are Vietnamese right ?

I_love_vov

Yeah Btw, he has Le Quy Don Online Judge account tho

-hk

I appreciate the effort but I think if you make cheater posts, you should focus on those where it's obvious. Admittedly, this case has some amount of evidence but with the rise of AI, there is also the rise of false positives either by the community (greateric being a great example), or just in general (skipped contests now have had several false positives).

I really think the only genuinely viable example is either very AI generated looking comments/ code patterns !cin etc, very odd times betweeen solutions, verifiably copied code, or jump in performance i.e going from pupil performance to GM performance in <1 month.

-16

To be honest, catching cheaters nowadays are much harder. Both cheaters and AI are so smart now. I make cheater exposing blogs for entertainment purpose only btw. I find it interesting to outsmart a cheater.

DuyMinh3005

Bro used a little bit too much the word "cheaters"

← Rev. 2 →

-11

ermactually

CHETEAR GAT TOLETN AND DUIMYNH3050 IS SAME!!! NO JOEK

You know what, ermactually = wrusb = kreukpg.

wrusb and kreukpg's code both have "made by Phongln"

SON

Yes, I know, I also know that kreukpg is a cheater (he admitted in one of his blogs). However, I don't think that wrusb cheated, maybe because he is so active at cheater exposing.

And CheaterGotTalent is not my alt. He is just one of my friends irl (he has his own main acc too)

MyBrainGotTLE

"cheetah gyatt toilet" xD

srvntofthejudge

There's an explanation for some AI patterns like !cin or oghers, github copilot autocomplete (which is allowed) can sometimes automatically change a part of your code your cursor is not on (which generally happens if you change a variable but can sometimes do other things), that happened to me once. and now theres a !cin in my submissions for div 3 F

+10

Yes, this is another good example.

greateric

+24

I'm still waiting for the day someone clueless tries to expose me

Euclid73

good idea for a blog post :)

Metall1cA

but you have 0 skipped contests.

+11

I will post one in the future (as a joke of course)

SisyphusPath

I appreciate your work keep on doing it. Upvoted

I appreciate your upvote. Upvoted.

bill_s

I appreciate your upvote. Upvoted

YOLU_gargaring

what is the plugin that display the rating of problems int the submission column

Sadman7

https://codeforces.me/topic/139870/en1

blackhatty

hey new guys!!

Don't be sad like lets solve some hard problems by ourself like when AC will come that is out real victory not rating right . Increase question rating level and getting AC and unlocking the question is real fun .

solving hard problems like mapping them first we have to do this then this then this and tle checks while coding is real fun not rating right guys ?

with cheater our TAG goal to reach some certain level will take more time ofc but we will reach there if we will grind

//what cheater will do with this TAG in interview and OAs when there is 1on1 interview then ?????//

:-)

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