Find the Zero

    1#include <bits/stdc++.h>
    2using namespace std;
    3using ll = long long;
    4using i128 = __int128;
    5const int inf = 1e9;
    6const ll INF = 1e18; //❄️
    7int qry(int i, int j) {
    8    cout << "? " << i << " " << j << endl;
    9    cout.flush();
    10    int ans; cin >> ans;
    11    return ans;
    12}
    13void solve() {
    14    int n; cin >> n;
    15    if (qry(1, 2) == 1) {
    16        cout << "! " << 1 << endl;
    17        cout.flush();
    18        return;
    19    }
    20    if (qry(2, 3) == 1) {
    21        cout << "! " << 2 << endl;
    22        cout.flush();
    23        return;
    24    }
    25    if (qry(1, 3) == 1) {
    26        cout << "! " << 1 << endl;
    27        cout.flush();
    28        return;
    29    }
    30    for (int i = 4; i <= 2 * n - 2; i += 2) {
    31        if (qry(i, i + 1) == 1) {
    32            cout << "! " << i << endl;
    33            cout.flush();
    34            return;
    35        }
    36    }
    37    cout << "! " << 2 * n << endl;
    38    cout.flush();
    39}
    40int main() {
    41    ios::sync_with_stdio(0); cin.tie(0); 
    42    int t; cin >> t;
    43    while (t--) {
    44        solve();
    45    }
    46    return 0;
    47}