uva 11078

#include<cstdio>
#include<cstdlib>
#include<cstring>
#include<cmath>
#include<iostream>
#include<algorithm>

using namespace std;

#define INF 0x7f7f7f7f
#define MAXN (100000+5)

int read[MAXN];

int main(){
	int T;
	scanf("%d", &T);
	
	while(T--){
		int n;
		scanf("%d", &n);
		for(int i = 1; i <= n; i++) scanf("%d", &read[i]);
		
		int maxi = read[1], ans = -INF;
		for(int j = 2; j <= n; j++){
			ans = max(ans, maxi - read[j]);
			maxi = max(maxi, read[j]);
		}
		
		printf("%d\n", ans);
	}
	
	return 0;
}