#include <bits/stdc++.h>
 
using namespace std;
#define int long long
#define yes cout << "YES\n";
#define no cout << "NO\n";
 
 
void FastIO(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);
}
 
void solve(){
    int n;
    cin >> n;
 
    vector<int> vec(n);
 
    for(int i = 0; i < n; i++){
        cin >> vec[i];
    }
 
    int ans = 0;
 
    for(int i = 0; i < n - 1; i++){
        ans = max(ans , vec[n-1] - vec[i]);
    }
 
    for(int i = 1; i < n; i++){
        ans = max(ans , vec[i] - vec[0]);
    }
 
    for(int i = 0; i < n-1; i++){
        ans = max(ans , vec[i] - vec[i+1]);
    }
 
    cout << ans << '\n';
}
 
 
signed main(){
    FastIO();
 
    int t = 1;
    cin >> t;
 
    while (t--){
        solve();
    }
    return 0;
}
 

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

NQo2CjEgMyA5IDExIDUgNwoxCjIwCjMKOSA5OSA5OTkKNAoyIDEgOCAxCjMKMiAxIDU=

5
6
1 3 9 11 5 7
1
20
3
9 99 999
4
2 1 8 1
3
2 1 5