Coding/D_Lost_Tree.cpp at main · nishantlamba29/Coding · GitHub

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

vector<int> query(int n, int r) {
    cout << "? " << r << endl;
    vector<int> dist(n + 1);
    for(int i=1;i<=n;i++) cin >> dist[i];
    return dist;
}

int32_t main(){
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    cout.tie(nullptr);

    int n;
    cin >> n;

    set<pair<int, int>> edges;
    queue<int> q;
    q.push(1);

    vector<int> vis(n + 1);
    while(!q.empty()) {
        int r = q.front();
        q.pop();
        vis[r] = 1;
        vector<int> dist = query(n, r);

        int even = 0, odd = 0;
        for(int i=1;i<=n;i++) {
            if(dist[i] % 2 == 0) even++;
            else odd++;
        }

        for(int i=1;i<=n;i++) {
            if(dist[i] == 1) {
                edges.insert({min(i, r), max(i, r)});
            }
        }
        if(edges.size() == n - 1) break;
        if(odd < even) {
            for(int i=1;i<=n;i++) {
                if(vis[i]) continue;
                if(dist[i] % 2 == 1) q.push(i);
            }
        }
        else {
            for(int i=1;i<=n;i++) {
                if(vis[i]) continue;
                if(dist[i] % 2 == 0) q.push(i);
            }
        }

    }

    cout << "!" << endl;
    for(auto &[u, v] : edges) {
        cout << u << " " << v << endl;
    }

    return 0;
}