Submission #1037375

#	Time	Username	Problem	Language	Result	Execution time	Memory
1037375		vjudge1	Network (BOI15_net)	C++17	100 / 100	219 ms	47952 KiB

net

#include <bits/stdc++.h>
using namespace std;
 
#define ll long long
#define ld long double
#define pii pair<int, int>
#define pll pair<ll, ll>
#define pld pair<ld, ld>
#define pb push_back
#define fi first
#define se second
#define debug(x) cout << #x << " => " << x << endl
#define all(x) x.begin(),x.end()

vector<int> adj[500010];
vector<int> v;

void dfs(int u,int p)
{
	if(adj[u].size()==1) v.pb(u);
	for(auto i : adj[u])
	{
		if(i!=p)
		{
			dfs(i,u);
		}
	}
}

int main()
{
	ios_base::sync_with_stdio(false); cin.tie(NULL); cout.tie(NULL);
	int n;cin>>n;
	for(int i=1;i<n;i++)
	{
		int u,v;cin>>u>>v;
		adj[u].pb(v);
		adj[v].pb(u);
	}
	for(int i=1;i<=n;i++)
	{
		if(adj[i].size()>1)
		{
			dfs(i,-1);
			break;
		}
	}
	vector<pii> ans;
	int mid=v.size()/2;
	for(int i=0;i<mid;i++)
	{
		ans.pb({v[i],v[i+mid]});
	}
	if(v.size()&1) ans.pb({v[0],v.back()});
	cout<<ans.size()<<'\n';
	for(auto i : ans) cout<<i.fi<<' '<<i.se<<'\n';
	return 0;
}

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