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#include <bits/stdc++.h>
using namespace std;
using ll = long long;
using pii = pair<int, int>;
using vpii = vector<pii>;
using vi = vector<int>;
using vll = vector<long long>;
using mpii = map<int, int>;
using mpll = map<ll, ll>;
using db = long double;
#define pb push_back
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define lb lower_bound
#define ub upper_bound
#define make_unique(x) \
sort(all((x))); \
(x).resize(unique(all((x))) - (x).begin())
#define ceil(a, b) ((a) + (b)-1) / (b)
const int mod = (int)1e9 + 7;
const db pi = acos((db)-1);
const int dx[4]{1, 0, -1, 0};
const int dy[4]{0, 1, 0, -1};
#ifdef LOCAL
#include "debug.h"
#else
#define dbg(...) 42
#endif
/* stuff you should look for:
---------------------------
* special cases (n=1?)
* int overflow, array bounds
* do smth instead of nothing and stay organized
* WRITE STUFF DOWN
* DON'T GET STUCK ON ONE APPROACH
*/
void solve() {
int n;
cin >> n;
vi v(n);
for (auto &x : v) {
cin >> x;
}
int cnt_front = 0;
int cnt_back = 0;
for (int i = 0; i < n - 1; i++) {
dbg(v[i + 1], v[i]);
if (v[i + 1] == v[i]) {
cnt_front++;
} else {
break;
}
}
for (int i = n - 1; i >= 0; i--) {
if (v[i - 1] == v[i]) {
cnt_back++;
} else {
break;
}
}
if (cnt_front == n - 1 && cnt_back == n - 1) {
cout << -1 << '\n';
return;
}
if (cnt_front == 0 || cnt_back == 0) {
cout << 0 << '\n';
return;
}
cnt_front++;
cnt_back++;
cout << min(cnt_front, cnt_back) << '\n';
}
int main() {
ios_base::sync_with_stdio(false);
cin.tie(NULL);
int tt;
cin >> tt;
while (tt--) {
solve();
}
}
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