Submission #1127066

#	Time	Username	Problem	Language	Result	Execution time	Memory
1127066		JelalTkm	Network (BOI15_net)	C++20	100 / 100	324 ms	43136 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);
    }

    int x;
    for (int i = 1; i <= n; i++)
      if ((int) g[i].size() == 1) {
        x = i;
        break;
      }

    vector<int> a;
    queue<int> q;
    vector<bool> visited(n + 1);
    q.push(x);
    visited[x] = 1;
    while (!q.empty()) {
      auto u = q.front();
      q.pop();
      if ((int) g[u].size() == 1)
        a.push_back(u);
      for (auto v : g[u])
        if (!visited[v]) {
          q.push(v);
          visited[v] = 1;
        }
    }

    cout << (((int) a.size() + 1) >> 1) << '\n';
    for (int i = 0; i < (int) a.size() >> 1; i++)
      cout << a[i] << " " << a[i + ((int) a.size() >> 1)] << '\n';
    if ((int) a.size() & 1)
      cout << a[(int) a.size() - 1] << " " << a[0] << '\n';
  }
 
  return 0;
}

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