Submission #655925

#	Time	Username	Problem	Language	Result	Execution time	Memory
655925		Behradm	Network (BOI15_net)	C++17	100 / 100	412 ms	40812 KiB

net

/*\ In The Name Of GOD
 *  Beyrad :D
\*/
#include "bits/stdc++.h"

#define sz(x) ((int) (x).size())

using namespace std;

const int N = 5e5 + 11;
int st[N];
int T = 0;
vector<int> g[N];

void dfs(int u, int p) {
  st[u] = T++;
  for (int v : g[u]) {
    if (v != p)
      dfs(v, u);
  }
}

signed main() {
  ios::sync_with_stdio(false);
  cin.tie(0), cout.tie(0);
  int n;
  cin >> n;
  for (int i = 0; i < n - 1; i++) {
    int u, v;
    cin >> u >> v;
    --u, --v;
    g[u].push_back(v);
    g[v].push_back(u);
  }

  int rt = 0;
  for (int i = 0; i < n; i++)
    if (sz(g[i]) >= 2)
      rt = i;

  dfs(rt, -1);
  vector<pair<int, int>> a;
  for (int i = 0; i < n; i++)
    if (sz(g[i]) == 1)
      a.emplace_back(st[i], i);

  sort(a.begin(), a.end());
  int k = sz(a);
  cout << (k + 1) / 2 << '\n';
  for (int i = 0; i < k / 2; i++)
    cout << a[i].second + 1 << " " << a[i + (k + 1) / 2].second + 1 << '\n';
  if (k % 2 == 1)
    cout << a[k / 2].second + 1 << " " << rt + 1 << '\n';
  return 0;
}

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