Submission #502602

#	Time	Username	Problem	Language	Result	Execution time	Memory
502602		NaimSS	Network (BOI15_net)	C++14	100 / 100	415 ms	47812 KiB

net

#include <bits/stdc++.h>
#define ld long double
#define endl "\n"
#define fastio ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define pb push_back
#define mp(a,b) make_pair(a,b)
#define ms(v,x) memset(v,x,sizeof(v))
#define all(v) v.begin(),v.end()
#define ff first
#define ss second
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define per(i, a, b) for(int i = b-1; i>=a ; i--)
#define trav(a, x) for(auto& a : x)
#define allin(a , x) for(auto a : x)
#define Unique(v) sort(all(v));v.erase(unique(all(v)),v.end());
#define sz(v) ((int)v.size())
using namespace std;
typedef vector<int> vi;
#define y1 abacaba
//#define left oooooopss
#define db(x) cerr << #x <<" == "<<x << endl;
#define db2(x,y) cerr<<#x <<" == "<<x<<", "<<#y<<" == "<<y<<endl;
#define db3(x,y,z) cerr << #x<<" == "<<x<<", "<<#y<<" == "<<y<<", "<<#z<<" == "<<z<<endl;
typedef long long ll;
typedef pair<int,int> pii;
typedef pair<ll,ll> pll;
typedef vector<ll> vl;
std::mt19937 rng((int) std::chrono::steady_clock::now().time_since_epoch().count());
ll cdiv(ll a, ll b) { return a/b+((a^b)>0&&a%b); } // divide a by b rounded up
ll fdiv(ll a, ll b) { return a/b-((a^b)<0&&a%b); } // divide a by b rounded down
inline ll mod(ll n, ll m ){ ll ret = n%m; if(ret < 0) ret += m; return ret; }
ll gcd(ll a, ll b){return (b == 0LL ? a : gcd(b, a%b));}
ll exp(ll b,ll e,ll m){
  b%=m;
  ll ans = 1;
  for (; e; b = b * b % m, e /= 2)
      if (e & 1) ans = ans * b % m;
  return ans;
}

// debug:
void dbg_out() { cerr << endl; }
template<typename Head, typename... Tail> void dbg_out(Head H, Tail... T){ 
  cerr << ' ' << H; 
  dbg_out(T...); 
}
#ifdef LOCAL
#define dbg(...) cerr<<"(" << #__VA_ARGS__<<"):" , dbg_out(__VA_ARGS__) , cerr << endl
#else
#define dbg(...) 
#endif
//

const int N = 500100;
vi g[N];
vi vec;
void dfs(int v,int p=-1){
  if(sz(g[v])==1){
    vec.pb(v);
  }
  for(auto to : g[v])if(to!=p){
    dfs(to,v);
  }
}
int32_t main(){
  fastio;
  int n;
  cin >> n;
  rep(i,0,n-1){
    int a,b;
    cin >> a >> b;
    g[a].pb(b);
    g[b].pb(a);
  }
  
  int root=1;
  while(sz(g[root])==1)root++;

  dfs(root);
	vector<pii> res;
  int t = sz(vec)/2;
  rep(i,0,sz(vec)){
    if(i + t >= sz(vec))break;
    res.pb(pii(vec[i],vec[i + t]));
  }
  cout<<sz(res)<<endl;
  for(auto it : res)cout<<it.ff<<" "<<it.ss<<endl;

	// math -> gcd it all
  // Did u check N=1? Did you switch N,M?
}

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