
// Problem: A. Robot Program
// Contest: Codeforces - Educational Codeforces Round 98 (Rated for Div. 2)
// URL: https://codeforces.com/contest/1452/problem/A
// Memory Limit: 256 MB
// Time Limit: 2000 ms
// Powered by CP Editor (https://github.com/cpeditor/cpeditor)

#include <bits/stdc++.h>

using namespace std;

#define fi first
#define se second
#define pb push_back
#define int long long
#define F(i, n) for (int i = 0; i < n; i++)
#define all(x)(x).begin(), (x).end()

using ld = long double;
using vi = vector <int>;
using mi = map <int, int>;
using pii = pair <int, int>;

const int N = 100005;
const int MOD = 1e9 + 7;

#define show(arr) { for (auto x: arr) cout << x << " "; cout << '\n'; }
#define show_(arr, n) F(i, n) show(arr[i])

void solve() {
	int n; cin>>n;
	int a[n],sum=0,mx=0;
	F(i,n){
		cin>>a[i];
		sum+=a[i];
		mx=max(mx,a[i]);
	}
	cout<<max((n-1)*((sum+n-2)/(n-1)),mx*(n-1))-sum<<'\n';
}
int32_t main() {
   ios::sync_with_stdio(false);
   cin.tie(0);
   cout.tie(0);

   int32_t t=1;
   cin >> t;
   while (t--) solve();

   return 0;
}