#include <bits/stdc++.h>
using namespace std;
int main() {
  int t;
  cin >> t;
  while (t--) {
    int n;
    cin >> n;
    int arr[n];
    for (int i = 0; i < n; i++) cin >> arr[i];
    long long int ans = 0;
    if (n != 1) {
      for (int i = 0; i < n - 1; i++) {
        ans += max(arr[i] - arr[i + 1], 0);
      }
    }
    cout << ans << endl;
  }
}
