#include<bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define pii pair<int,int>
using namespace std;
long long mod=1000000007;
ll gcd(ll a, ll b) 
{ 
    if (b == 0) 
        return a; 
    return gcd(b, a % b); 
} 
void solve()
{
    ll n;cin>>n;
    ll a[n];
    ll sum=0;
    for(int i=0;i<n;i++) cin>>a[i],sum+=a[i];
    sort(a,a+n);
    ll req=(sum+n-2)/(n-1);
   // cout<<req<<" ";
    ll ans=req*(n-1);
    if(req<a[n-1]) ans=a[n-1]*(n-1);
    cout<<ans-sum<<endl;
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(0);cout.tie(0);
    int t;cin>>t;
    while(t--)
    {
        solve();
    }
    return 0;
}
