I was trying to solve this problem but my solution keeps failing and i don't know why. I'd really appreciate if someone could help me identify what I'm getting wrong.

#include <algorithm>
#include <vector>
#include <numeric>
#include <iostream>
using namespace std;
static void paveway(){
	long long n; cin >> n; vector<long long> a(n); long long ans = 1 , ant = 1;
	for(long long i = 0; i < n; i++){cin >>  a[i];}
	for(long long i = 0; i < n - 1; i++){
		if(a[i] != a[i+1]){
			break;
		}
		ans++;
	}
	reverse(a.begin(),a.end());
	for(long long i = 0; i < n - 1; i++){
		if(a[i] != a[i+1]){
			break;
		}
		ant++;
	}
	if(ans == n && ant == n) cout << -1 << endl; else cout << min(ans , ant) << endl;
}
int main(){ 
	ios::sync_with_stdio(false);
	cin.tie(nullptr);
	long long t; cin >> t;
	for(;t--;)
	paveway();
return 0;
}