Submission #1111484

#	Time	Username	Problem	Language	Result	Execution time	Memory
1111484		Kirill22	Network (BOI15_net)	C++17	100 / 100	375 ms	44216 KiB

net

#include "bits/stdc++.h"
 
using namespace std;
 
void solve() {
    int n;
    cin >> n;
    vector<vector<int>> g(n);
    for (int i = 0, x, y; i + 1 < n; i++) {
        cin >> x >> y;
        x--, y--;
        g[x].push_back(y);
        g[y].push_back(x);
    }
    int rt = 0;
    while ((int) g[rt].size() == 1) {
        rt++;
    }
    vector<int> leafes;
    auto dfs = [&] (auto&& dfs, int v, int pr) -> void {
        if ((int) g[v].size() == 1) {
            leafes.push_back(v);
        }
        for (auto u : g[v]) {
            if (u != pr) {
                dfs(dfs, u, v);
            }
        }
    };
    dfs(dfs, 0, 0);
    int sz = (int) leafes.size();
    vector<pair<int, int>> ans;
    if (sz % 2 == 0) {
        for (int i = 0; i < sz / 2; i++) {
            ans.push_back({leafes[i], leafes[i + sz / 2]});
        }
    } else {
        for (int i = 0; i < sz / 2; i++) {
            ans.push_back({leafes[i], leafes[i + sz / 2]});
        }
        ans.push_back({leafes[0], leafes.back()});
    }
    cout << (int) ans.size() << '\n';
    for (auto& [x, y] : ans) {
        cout << x + 1 << " " << y + 1 << '\n';
    }
}
 
int main() {
    ios_base::sync_with_stdio(0);
    cin.tie(0);
    cout.tie(0);
    int t = 1;
//    cin >> t;
    while (t--) {
        solve();
    }
}

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