Submission #849585

#	Time	Username	Problem	Language	Result	Execution time	Memory
849585		dungz	Network (BOI15_net)	C++17	100 / 100	358 ms	47824 KiB

net

//#pragma GCC optimize ("O2")
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define fi first
#define se second
#define endl '\n'
#define task "task"
#define task "task"
#define prll pair<ll,ll>
#define pb push_back
#define ld long double
const ll MIN=-1e18,MAX=1e18,MOD=1e9+7;
vector<int> a[500005];
vector<int> leaves;
void dfs(int u,int par)
{
	if(a[u].size()==1) leaves.push_back(u);
	for(auto i:a[u])
	{
		if(i!=par)
		{
			dfs(i,u);
		}
	}
}
int main(){
   	//freopen (task".inp", "r", stdin);
   	//freopen (task".out", "w", stdout);
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	int n;
	cin>>n;
	leaves.push_back(0);
	for(int i=1;i<n;i++)
	{
		int x,y;
		cin>>x>>y;
		a[x].push_back(y);
		a[y].push_back(x);
	}
	dfs(1,0);
//	for(auto i:leaves) cout<<i<<" ";
//	cout<<endl;
	if(leaves.size()%2==1)
	{
		cout<<leaves.size()/2<<endl;
		for(int i=1;i<=leaves.size()/2;i++)
		{
			cout<<leaves[i]<<" "<<leaves[i+leaves.size()/2]<<endl;
		}
//		if(leaves.size()%2==01)cout<<leaves[leaves.size()/2]<<" "<<1<<endl;
	}
	else
	{
		cout<<leaves.size()/2<<endl;
		for(int i=1;i<=leaves.size()/2-1;i++)
		{
			cout<<leaves[i]<<" "<<leaves[i+leaves.size()/2]<<endl;
		}
		cout<<leaves[leaves.size()/2]<<" "<<1<<endl;
	}
}
/*

*/

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:47:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   47 |   for(int i=1;i<=leaves.size()/2;i++)
      |               ~^~~~~~~~~~~~~~~~~
net.cpp:56:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   56 |   for(int i=1;i<=leaves.size()/2-1;i++)
      |               ~^~~~~~~~~~~~~~~~~~~

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