#include <bits/stdc++.h>
using namespace std;
int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  long long t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int a[n];
    for (int i = 0; i < n; i++) {
      cin >> a[i];
    }
    int cmax = a[0], cmin = INT_MAX;
    long long ans = 0;
    for (int i = 1; i < n; i++) {
      if (a[i] < a[i - 1]) {
        ans += a[i - 1] - a[i];
      }
    }
    cout << ans << "\n";
  }
}
