Submission #931856

#	Time	Username	Problem	Language	Result	Execution time	Memory
931856		Erfan1386Y	Network (BOI15_net)	C++14	100 / 100	320 ms	47696 KiB

net

#include <bits/stdc++.h>
#define file_io freopen("input.txt", "r", stdin);freopen("output.txt", "w", stdout);
#define fast_io ios::sync_with_stdio(false);cin.tie(0);
#define what(x) cerr << #x << " is " << x << '\n';
#define kill(x) {cout << x << endl; return 0;}
#define all(x) (x).begin(), (x).end()
#define pii pair<int, int>
#define pb push_back
#define ll long long
#define F first
#define S second
const ll inf = 1e18, mod = 1e9 + 7, delta = 1e9 + 9, SQ = 450, P = 6065621;
 
using namespace std;

const int N = 5e5 + 10, LG = 40;
vector<int> adj[N], l;

void dfs (int v, int p = -1) {
  if (adj[v].size() == 1) l.pb(v);
  for (auto u: adj[v])
    if (u - p) dfs(u, v);
}

int main () {
  fast_io;
  int n;
  cin >> n;
  for (int i = 1; i < n; i++) {
    int u, v;
    cin >> u >> v;
    adj[u].pb(v);
    adj[v].pb(u);
  }
  dfs(1);
  cout << (l.size() + 1) / 2 << '\n';
  int t = (l.size() + 1) / 2;
  for (int i = 0; i < t; i++)
    cout << l[i] << ' ' << l[i + l.size() / 2] << '\n'; 
  return 0;
}

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