1788A - One and Two - CodeForces Solution

#include <bits/stdc++.h>

using namespace std;
typedef long long ll;
typedef unsigned long long ull;
#define output(v) for(auto&it:v){cout<<it<<" ";}cout<<"\n"
#define input(v) for(auto&it:v){cin>>it;}
#define watch(x) cerr<<#x<<" : "<<x<<endl;
#define all(v) v.begin(),v.end()
#define allr(v) v.rbegin(),v.rend()
void FastCode() {
    std::ios_base::sync_with_stdio(false);
    cin.tie(NULL);
    cout.tie(NULL);
}
void File(){
//    freopen("equal.in", "r", stdin);
//        freopen("373.in", "w", stdout);
}
void preprocessing(){

}
void testCase(int ct) {
    int n;
    cin >> n;
    ll arr[n+1] = {};
    arr[0] = 0;
    for(int i = 1 ; i <= n ;i++){
        cin >> arr[i];
        if(arr[i] == 1) arr[i] = 0;
        else arr[i] = 1;
        arr[i]+=arr[i-1];
    }
    for(int i = 1 ; i < n ;i++){
        if(arr[i] == arr[n]-arr[i]){
            cout<<i<<"\n";
            return;
        }
    }
    cout<<"-1\n";
}
int32_t main(){
    FastCode();
    File();
    preprocessing();
    int t = 1;
    cin >> t;
    for(int i = 1 ; i <= t ;i++)
        testCase(i);
    return 0;
}