Submission #170880

#	Time	Username	Problem	Language	Result	Execution time	Memory
170880		nafis_shifat	Network (BOI15_net)	C++14	0 / 100	13 ms	12028 KiB

net

#include<bits/stdc++.h>
#define pii pair<int,int>
#define ll long long
#define s second
using namespace std;
const int mxn=5e5+6;
vector<int> tree[mxn];



int k=1;
int _tm[mxn];

vector<pii> lf;


int root=1;
void dfs(int cur,int prev)
{
	_tm[cur]=k++;
	if(tree[cur].size()==1 && cur!=root)lf.push_back({_tm[cur],cur});

	for(int i:tree[cur])
	{
		if(i!=prev)
		{
			dfs(i,cur);
		}
	}

}
int main()
{
	int n;
	cin>>n;
	for(int i=1;i<n;i++)
	{
		int u,v;
		cin>>u>>v;
		tree[u].push_back(v);
		tree[v].push_back(u);


	}
	
	

	for(int i=1;i<=n;i++)
	{
	    if(tree[i].size()>1)
	    {
	        root=i;
	        break;
	    }
	}
	
	dfs(root,-1);
	sort(lf.begin(),lf.end());
	int r=lf.size();
	cout<<(r+1)/2<<endl;



	for(int i=0;i<(r+1)/2;i++)
	{
		if(i!=r-1-i)
		    cout<<lf[i].s<<" "<<lf[r-1-i].s<<endl;
		else
			cout<<root<<" "<<lf[i].s<<endl;
	}









	return 0;
}

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