#include <bits/stdc++.h>
#include <cmath>
#include <regex>
#define ff first
#define ss second
#define pb push_back
#define mp make_pair
#define ba back
#define ppb pop_back
#define eb emplace_back
#define eps 1e-6
#define vec vector<long long int>
#define sz(x) (int((x.size())))
#define all(x) (x).begin(),(x).end()
#define FAST ios_base :: sync_with_stdio (false); cin.tie (NULL)
#define ll long long
#define loop(i,s,n) for(int i=s;i<n;i++)
using namespace std;
//-----------------------------------------------------------------------------------------------------------------
const ll M = 1e9 + 7;
const ll N = 2e5 + 5;
const ll inf = 2e18;
ll mod(ll x){   return (x%M);}
ll mod_minus(ll a, ll b){ ll ans= (mod(a)-mod(b)); if(ans<0) ans=mod(ans+M); return ans;}
 
ll mod_mul(ll a,ll b){  return mod(mod(a)*mod(b));}
 
ll mod_add(ll a,ll b){ return mod(a+b);}
 
ll power(ll a,ll n){  
    if(n==0) return 1; 
     else if(n==1) return a; 
      ll R=power(a,n/2)%M; 
       if(n%2==0) {    return mod(mod_mul(R,R));  } 
    
      else {   return mod(mod_mul(mod_mul(R,a),mod(R)));  }
    }
 
ll mod_inv(ll n){  return power(n,M-2);}
 
// only if M is prime
ll mod_div(ll a,ll b){  
     ll ans=mod(a);   ll b1=power(b,M-2); 
       ans= mod(mod_mul(ans,b1));  
        return ans;
        }
 
ll fact_mod(ll n){ 
    vec fact(n+1);
     fact[0]=1;   
     loop(i,1,n+1){  
          fact[i]=mod_mul(fact[i-1],i);
           }  
            return fact[n];
    }
 
unsigned long long nCr_mod(unsigned long long n,  ll r) 
{ 
    if (r == 0) 
        return 1; 
    unsigned long long fac[n + 1]; 
    fac[0] = 1; 
    for (int i = 1; i <= n; i++) 
        fac[i] = (fac[i - 1] * i) % M; 
  
    return (fac[n] * mod_inv(fac[r]) % M * mod_inv(fac[n - r]) % M) % M; 
} 
//--------------------------------------------------------------------------------------------------------------
void solve(){
    ll n;
    cin>>n;
    ll a[n];
    ll sum=0;
    loop(i,0,n){
        cin>>a[i];
        sum+=a[i];
    }
    sort(a,a+n);
    ll mx=a[n-1],mn=a[0];
    ll z=(n-1)-sum%(n-1);
    if(z==(n-1)){
        z=0;
    }
    sum+=z;
    if(mx<=sum/(n-1)){
        cout<<z<<endl;
        return;
    }
    cout<<mx*(n-1)-sum+z<<endl;
}

int main(){
    FAST;
    int t;
    cin>>t;
    while(t--){
        solve();  
    }
}