// https://www.hackerrank.com/challenges/stockmax/

import java.io.*;

import java.util.*;

import java.text.*;

import java.math.*;

import java.util.regex.*;

public class Solution {

public static void main(String[] args) throws IOException {

BufferedReader ob = new BufferedReader(new InputStreamReader(System.in));

int testcase = Integer.parseInt(ob.readLine());

while(testcase-->0){

int n = Integer.parseInt(ob.readLine());

BigInteger [] stock = new BigInteger[n];

String[] tmp = ob.readLine().split(" ");

for (int i = 0; i < n; i++) {

stock[i] = new BigInteger(tmp[i]);

}

BigInteger profit = new BigInteger("0");

BigInteger currentMax = stock[n-1];

for (int i = n-2; i >=0 ; i--) {

if (currentMax.compareTo(stock[i]) < 0) {

currentMax = stock[i];

}

profit = profit.add(currentMax.subtract(stock[i]));

}

System.out.println(profit);

}

}

}