A_One_and_Two.cpp

#include <bits/stdc++.h>
using namespace std;

// Speed
#define fastio() ios_base::sync_with_stdio(false), cin.tie(nullptr), cout.tie(nullptr);

// Macros
typedef long long ll;
#define rep(i,j) for(int i=0;i<j;i++)
#define rrep(i,j) for(int i=j-1;i>=0;i--)
#define all(x) x.begin(), x.end()
#define pb push_back

// Binary
// string decToBinary(int n){string s="";int i = 0;while (n > 0) {s =to_string(n % 2)+s;n = n / 2;i++;}return s;},
// ll binaryToDecimal(string n){string num = n;ll dec_value = 0;int base = 1;int len = num.length();for(int i = len - 1; i >= 0; i--){if (num[i] == '1')dec_value += base;base = base * 2;}return dec_value;}

//shortcuts
#define yes cout<<"YES";
#define no cout<<"NO";
#define inp(x) int x; cin>>x;
#define inpl(x) ll x; cin>>x;
#define inp2(x,y) int x,y; cin>>x>>y;
#define inp2l(x,y) ll x,y; cin>>x>>y;
#define inp3(x,y,z) int x,y,z; cin>>x>>y>>z;
#define inp3l(x,y,z) ll x,y,z; cin>>x>>y>>z;
#define br cout<<'\n';
#define out(x) cout<<x;
#define outln(x) cout<<x<<'\n';

// Typedef
typedef pair<int, int> pi;
typedef vector<int> vi;
typedef map<int,int> mii;
typedef set<int> si;
typedef unordered_map<int,int> umii;
typedef unordered_map<char,int> umci;
typedef unordered_set<int> usi;
typedef unordered_set<ll> usll;

void solve(){
    inp(n);
    vi arr(n);
    int cnt=0;
    rep(i,n){
        cin>>arr[i];
        if(arr[i]==2) cnt++;
    }
    if(cnt%2==1) {
        out(-1);
        return;
    }
    int c=0;
    for(int i=0;i<n-1;i++){
        if(arr[i]==2){
            c++;
        }
        if(c==cnt/2){
            out(i+1);
            return;
        }
    }
}

int32_t main()
{
    fastio()
    int t;
    cin >> t;
    while(t--)
    {
        solve();
        br;
    }
    return 0;
}