436-all-are-same.cpp

/*
 * All are Same  [1593D1]
 * Problem:  https://codeforces.com/problemset/problem/1593/D1
 * Verdict:  ACCEPTED        Solved: 2021-10-13
 * Language: C++17 (GCC 7-32)
 * Runtime:  30 ms     Memory: 0 KB
 * Tags:     math, number theory
 * Author:   BidoTeima
 * Source:   https://codeforces.com/contest/1593/submission/131792997
 */

/// isA AC
#include <bits/stdc++.h>
using namespace std;
#include<ext/pb_ds/assoc_container.hpp>
#include<ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
template<typename _Ty>
using ordered_set = tree<_Ty,null_type,less<_Ty>,rb_tree_tag,tree_order_statistics_node_update>;
using ll = long long;
void ACPLS()
{
#ifndef ONLINE_JUDGE
    freopen("output.txt", "w", stdout);
    freopen("input.txt", "r", stdin);
#endif
    ios::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
}
#define tc         \
    int tttttt,subtask;    \
    cin >> tttttt /*>> subtask*/; \
    while (tttttt--)
 
#define sumrange(l, r, arr) (l == 0 ? arr[r] : arr[r] - arr[l - 1])
#define all(v) v.begin(), v.end()
ll gcd(ll a, ll b){
    if(b==0)
        return a;
    return gcd(b,a%b);
}
int main()
{
    ACPLS();
tc{
    int n;
    cin>>n;
    ll a[n];
    for(auto&i:a)cin>>i;
    ll g=0;
    sort(a,a+n);
    for(int i = 1; i < n; i++)
        g=gcd(g,a[i]-a[i-1]);
    cout<<(g==0?-1:g)<<'\n';
}
}