Submission #1127019

#	Time	Username	Problem	Language	Result	Execution time	Memory
1127019		JelalTkm	Network (BOI15_net)	C++20	0 / 100	0 ms	328 KiB

net

#include <bits/stdc++.h>
#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")

using namespace std;

#define int long long int

const int N = 2e1 + 10;
const int md = 1e9 + 7;
const int INF = 1e9;

int32_t main(int32_t argc, char *argv[]) {
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  
  int T = 1;
  // cin >> T;
  while (T--) {
    int n;
    cin >> n;
    vector<vector<int>> g(n + 1, vector<int> ());
    for (int i = 0; i < n - 1; i++) {
      int u, v;
      cin >> u >> v;
      g[u].push_back(v);
      g[v].push_back(u);
    }

    set<int> s;
    for (int i = 1; i <= n; i++)
      if ((int) g[i].size() == 1)
        s.insert(i);

    cout << (((int) s.size() + 1) >> 1) << '\n';
    int x = (*s.begin());
    queue<int> q;
    q.push(x);
    vector<bool> visited(n + 1);
    int ans;
    while (!q.empty()) {
      auto u = q.front();
      q.pop();
      if ((int) g[u].size() == 1)
        ans = u;
      for (auto v : g[u])
        if (!visited[v]) {
          q.push(v);
          visited[v] = 1;
        }
    }

    cout << x << " " << ans << '\n';
    s.erase(x), s.erase(ans);
    while ((int) s.size() > 1) {
      cout << *s.begin() << " " << *(--s.end()) << '\n';
      s.erase(s.begin());
      s.erase(--s.end());
    }
    if ((int) s.size() == 1) {
      cout << *s.begin() << " " << x << '\n';
    }
  }
 
  return 0;
}

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