Submission #931662

#	Time	Username	Problem	Language	Result	Execution time	Memory
931662		vjudge1	Network (BOI15_net)	C++17	0 / 100	2 ms	5360 KiB

net

/// ITNOG
#include <bits/stdc++.h>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/tree_policy.hpp>
//#pragma GCC optimize("O3,unroll-loops")
//#pragma GCC target("avx2,bmi,bmi2,lzcnt,popcnt")
#define F first
#define S second
#define pb push_back
#define ppb pop_back
#define fast_io ios::sync_with_stdio(false);cin.tie(NULL);
#define file_io freopen("input.txt","r",stdin);freopen("output.txt","w",stdout);
#define FOR(i,k,n) for(int i = k; i < n; ++ i)
#define debf cout<<"(0-0)\n";
#define all(x) x.begin(), x.end()
#define dec(x) cout << fixed << setprecision(x);
#define pf push_front
#define ppf pop_front
#define dash " ------- "
#define what(x) cerr << #x << " is " << x << endl;
#define eb emplace_back
//#define int short int
#define int long long
#define sz(s) (int) (s.size())
#define fl cout.flush()

using namespace std;
//using namespace __gnu_pbds;

typedef long long ll;
typedef pair <int, int> pii;
typedef pair <int, pii> pip;
typedef pair <pii, int> ppi;
typedef pair <ll, ll> pll;
typedef unsigned long long ull;
typedef long double ld;

template <class T> using max_heap = priority_queue <T, vector <T>, less <T> >;
template <class T> using min_heap = priority_queue <T, vector <T>, greater <T> >;
//template <class T> using ordered_set = tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;

constexpr int MOD = 1e9 + 7, N = 2e5 + 8, M = 1e6, SQ = 600, INF = 1e15 + 8, LGN = 22, mod = 998244353, P = 131113;

mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());

int n, leaf, x;
vector <int> v;
vector <int> adj[N];

int32_t main(){
  fast_io;
  cin >> n;
  FOR (i, 0, n - 1){
    int aa, bb;
    cin >> aa >> bb;
    adj[--aa].pb(--bb);
    adj[bb].pb(aa);
  }
  FOR (i, 0, n){
    if (adj[i].size() == 1){
      ++ leaf;
      v.pb(i);
    }
    else {
      x = i;
    }
  }
  cout << (leaf + 1) / 2 << '\n';
  while (v.size() >= 2){
    cout << v.back() + 1 << " ";
    v.ppb();
    cout << v.back() + 1 << '\n';
    v.ppb();
  }
  if (v.size() == 1){
    cout << v.back() + 1 << " " << x + 1 << '\n';
  }
  return 0;
}

// Yesterday is history
// Tomorrow is a mystery
// but today is a gift
// That is why it is called the present

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