Submission #170903

#	Time	Username	Problem	Language	Result	Execution time	Memory
170903		nafis_shifat	Network (BOI15_net)	C++14	100 / 100	1460 ms	47796 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];

vector<int> lf;


int root=1;
void dfs(int cur,int prev)
{

	if(tree[cur].size()==1)lf.push_back(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);


	}
	

	dfs(root,-1);

	int r=lf.size();
	cout<<(r+1)/2<<endl;
	int md=(r+1)/2;
	

	for(int i=0;i<md;i++)
	{
		if(i+md<r)
		    cout<<lf[i]<<" "<<lf[i+md]<<endl;
		else
			cout<<lf[i]<<" "<<lf[r-1]<<endl;
	}









	return 0;
}

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