Submission #1225289

#	Time	Username	Problem	Language	Result	Execution time	Memory
1225289		kokoxuya	Network (BOI15_net)	C++20	100 / 100	643 ms	46952 KiB

net

#include <bits/stdc++.h>
using namespace std;
#define int long long
#define pb push_back
#define mp make_pair
#define pii pair<int,int>
#define ss second
#define ff first
#define piii pair<int,pii>
#define debu(x) (cerr << #x  << " = "<< x << "\n")
#define debu2(x,y) (cerr << #x  << " = "<< x << " " << #y << " = " << y << "\n")
#define debu3(x,y,z) (cerr << #x  << " = "<< x << " " << #y << " = " << y << " " << #z << " = " << z<< "\n")
#define bitout(x,y) {\
	cerr << #x << " : ";\
	for (int justforbits = y; justforbits >=0; justforbits--)cout << (((1 << justforbits) & x)>=1);\
	cout << "\n";\
}
#define rangeout(j,rangestart,rangeend) {\
	cerr << "outputting" << #j<< ":\n";\
	for (int forrang = rangestart; forrang <= rangeend; forrang++)cerr << j[forrang] << " ";\
	cerr<<"\n";\
}
#define c1 {cerr << "Checkpoint 1! \n\n";cerr.flush();}
#define c2 {cerr << "Checkpoint 2! \n\n";cerr.flush();}
#define c3 {cerr << "Checkpoint 3! \n\n";cerr.flush();}
#define c4 {cerr << "Checkpoint 4! \n\n";cerr.flush();}
#define defN 500001

vector<vector<int>>adjlist(defN);
vector<int>preorder(defN);
int curr=0;

void dfs(int cn)
{
	preorder[cn]=++curr;
	for(int to:adjlist[cn])
	{
		if(preorder[to])continue;
		dfs(to);
	}
}


signed main()
{
    int t1,t2,t3,t4;
    mt19937_64 rnd(chrono::high_resolution_clock::now().time_since_epoch().count());
    //ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	
	int n;cin>>n;
	for(int a=1;a<n;a++)
	{
		cin>>t1>>t2;
		adjlist[t2].pb(t1);
		adjlist[t1].pb(t2);
	}
	
	int myroot;
	for(int a=1;a<=n;a++)
	{
		if(adjlist[a].size()!=1)
		{
			myroot=a;break;
		}
	}
	
	dfs(1);
	
	vector<pii>myliz;
	for(int a=1;a<=n;a++)
	{
		if(adjlist[a].size()==1)
		{
			myliz.pb(mp(preorder[a],a));
		}
	}
	
	sort(myliz.begin(),myliz.end());
	cout<<myliz.size()/2+myliz.size()%2<<"\n";
	for(int a=0;a<myliz.size()/2;a++)
	{
		cout<<myliz[a].ss<<" "<<myliz[a+myliz.size()/2].ss<<"\n";
	}
	if(myliz.size()%2)cout<<myliz[myliz.size()/2].ss<<" "<<myliz[myliz.size()-1].ss<<"\n";
}

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