#include <map>
#include <set>
#include <list>
#include <cmath>
#include <ctime>
#include <deque>
#include <queue>
#include <stack>
#include <string>
#include <bitset>
#include <cstdio>
#include <limits>
#include <vector>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <fstream>
#include <numeric>
#include <sstream>
#include <iostream>
#include <algorithm>
#include <unordered_map>

using namespace std;

/*To make it singleton
class point{

    int localmin;
    int localmax;
    int x;
    int y;
    static point p;


};*/

int main(){



    int t;
    cin >> t;
    for(int a0 = 0; a0 < t; a0++){

    int max=0;
    long profit=0;

        int N;
        cin >> N;
        vector<int> prices(N);
        for(int prices_i = 0; prices_i < N; prices_i++){
           cin >> prices[prices_i];
            }

        for(int i=N-1; i>=0; i--)
        {
           if(i == (N-1)){
                max=prices[i];
            }
           else if(prices[i]>max){
                max=prices[i];
            }
           else if(max-prices[i]>0)
                {
                profit=profit+max-prices[i];
               }

          }
                cout<<profit<<"\n";


    }
    return 0;
}