Submission #1206745

#	Time	Username	Problem	Language	Result	Execution time	Memory
1206745		dksnfjkfnwkfw	Network (BOI15_net)	C++20	0 / 100	5 ms	12104 KiB

net

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

const int MAXN = 5e5 + 5;
int n;
vector<int> adj[MAXN];
int deg[MAXN];
bool used[MAXN];

int main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    cin >> n;
    for (int i = 1; i < n; ++i) {
        int u, v;
        cin >> u >> v;
        adj[u].push_back(v);
        adj[v].push_back(u);
        deg[u]++;
        deg[v]++;
    }

    // Tìm các lá
    vector<int> leaves;
    for (int i = 1; i <= n; ++i) {
        if (deg[i] == 1) leaves.push_back(i);
    }

    vector<pair<int, int>> res;
    int L = leaves.size();

    // Ghép cặp các lá
    for (int i = 0; i + 1 < L; i += 2) {
        res.emplace_back(leaves[i], leaves[i + 1]);
        used[leaves[i]] = used[leaves[i + 1]] = true;
    }

    // Nếu số lá lẻ → còn một lá chưa ghép
    if (L % 2 == 1) {
        int last = -1;
        for (int i = 1; i <= n; ++i) {
            if (!used[i] && deg[i] > 1) {
                last = i;
                break;
            }
        }
        res.emplace_back(leaves.back(), last);
    }

    // Output
    cout << res.size() << '\n';
    for (auto [u, v] : res) {
        cout << u << ' ' << v << '\n';
    }

    return 0;
}

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37