Thank you so much for taking your time to answer this. I really like your problem and explanation of it.

Oh so basically problem was that sum was int actually, I tought I already tried it as long long. Also I now see that in editorial int was defined as long long, idk why would someone do that, it's confusing to beginners but okay.

I think I've been missing something, this code gives wrong result for test case 6 1000, 6x -1000000000:

#define ll long long
const ll P = 1e9+7;

int main()
{
    int t;
    cin >> t;
    int kk = 0;
    while(t--)
    {
        int n, k;
        cin >> n >> k;
        vector<int> a(n);
        int sum = 0;
        for(int i = 0; i < n; i++)
        {
            cin >> a[i];

        }
        ll big = 0;
        ll subar = 0;
        for(int i = 0; i < n; i++)
        {
            sum += a[i] ;
            subar += a[i];
            subar = max(subar, 0LL);
            big = max(big, subar);
        }
        sum = (sum % P + P ) % P;
        big = big % P;

        int T = 1;
        for(int i = 0; i < k; i++)
        {
            T = T *2 % P;

        }
        int ans = (sum + big * T - big + P) % P;
        cout << ans<< endl;
    }
    return 0;
}

I can't really find the problem, I looked at the editorial code and it seems fine to me.

Also if anyone cares to elaborate, why can we use int for sum (like editorial does) can't that overflow the value, does OP knows that test cases won't to that, or is there something else that I'm missing?

I'm a bit confused, I guess I forgot registering for contest, and there's timer stating: "Before extra registration", yet I'm unable to register? New here. Edit: my bad

Thanks man, I can't believe I overlooked such a simple thing.

Can someone help me understand why my solution isn't working for A problem: https://codeforces.me/contest/1928/submission/245856620