/*
        By: facug91
        From:
        Name:
        Date: 14/04/2016
*/

#include <bits/stdc++.h>
#define endl "\n"
#define EPS 1e-9
#define MP make_pair
#define F first
#define S second
#define DB(x) cerr << " #" << (#x) << ": " << (x)
#define DBL(x) cerr << " #" << (#x) << ": " << (x) << endl
const double PI = acos(-1.0);

#define INF 1000000000
//#define MOD 1000000007ll
#define MAXN 100000005

using namespace std;
typedef long long ll;
typedef unsigned long long llu;
typedef pair<int, int> ii; typedef pair<ii, ii> iiii;
typedef vector<int> vi; typedef vector<ii> vii; typedef vector<iiii> viiii;

ll n, a[1000005], ans, mx;

int main () {
    #ifdef ONLINE_JUDGE
        ios_base::sync_with_stdio(0); cin.tie(0);
    #endif
    //cout<<fixed<<setprecision(3); //cerr<<fixed<<setprecision(3); //cin.ignore(INT_MAX, ' '); //cout << setfill('0') << setw(5)
    int tc = 1, i, j;

    cin>>tc;
    while (tc--) {
        cin>>n;
        for (i=0; i<n; i++) cin>>a[i];
        mx = -1; ans = 0;
        for (i=n-1; i>=0; i--) {
            if (a[i] > mx) mx = a[i];
            else ans += mx - a[i];
        }
        cout<<ans<<endl;
    }

    return 0;
}