#include <bits/stdc++.h>
using namespace std;

void solve() {
	int n;
	cin >> n;
	vector<long long> a(n);
	for (int i = 0; i < n; ++i) {
		cin >> a[i];
	}
	bool cred = true;
	for (int i = 1; i < n; ++i) {
		if (a[i - 1] >= a[i]) cred = false;
	}
	if (cred) {
		cout << 0 << "\n";
		return;
	}
	long long ans = 0;
	for (int i = 1; i < n; ++i) {
		if (a[i - 1] < a[i]) continue;
		ans = max(a[i - 1] - a[i] + 1, ans);
	}
	cout << ans << "\n";
}

int main() {
	ios_base::sync_with_stdio(false);
	cin.tie(nullptr);
	int test = 1;
	cin >> test;
	while (test--) {
		solve();
	}
	return 0;
}