#define _CRT_SECURE_NO_WARNINGS
#include <string>
#include <vector>
#include <queue>
#include <memory.h>
#include <algorithm>
#include <iostream>
#include <stack>
#include <unordered_set>
#include <math.h>

using namespace std;
int a[1000000] = { 0 };

int	main(void)
{
	cin.tie(NULL);
	cout.tie(NULL);
	ios_base::sync_with_stdio(false);
	freopen("input.txt", "r", stdin);
	int ts;
	cin >> ts;
	int n;

	while (ts--)
	{
		cin >> n;
		long long answer = 0;
		for (int i = 0; i < n; i++)
		{
			cin >> a[i];
		}
		int mmax = a[n - 1];
		for (int i = n - 2; i >= 0; i--)
		{
			mmax = max(a[i], mmax);
			if (a[i] < mmax)
				answer += mmax - a[i];
		}
		cout << answer << "\n";
	
	}
}