#include <iostream>
using namespace std;
int main()
{
    long long t;
    cin >> t;
    while(t--)
    {
        long long n, s = 0, mx = 0;
        cin >> n;
        long long a[n + 1];
        for(long long i = 1; i <= n; ++i){
            cin >> a[i];
            s += a[i];
            mx = max(mx, a[i]);
        }
        cout << max((n - 1) * mx, (s + n - 2) / (n - 1) *(n - 1)) - s << "\n";
    }
}
