Submission #394624

#	Time	Username	Problem	Language	Result	Execution time	Memory
394624		ali_tavakoli	Network (BOI15_net)	C++14	0 / 100	7 ms	11980 KiB

net

//In The Name Of Allah
#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
#define pb push_back
#define F first
#define S second
//#pragma GCC optimize("Ofast")

const int maxn = 5e5 + 5;

int n;
vector<int> adj[maxn], leaf;

void dfs(int v, int p = 0)
{
	if(adj[v].size() == 1)
		leaf.pb(v);
	for(auto u : adj[v])
		if(u != p)
			dfs(u, v);
}

int main()
{
	ios::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin >> n;
	for(int i = 0; i < n - 1; i++)
	{
		int a, b;
		cin >> a >> b;
		adj[a].pb(b);
		adj[b].pb(a);
	}

	for(int i = 1; i <= n; i++)
		if(adj[i].size() > 1)
		{
			dfs(i);
			break;
		}
	
	cout << (leaf.size() + 1) / 2 << '\n';

	for(int i = 0; i < (leaf.size() + 1) / 2; i ++)
	{
		if(leaf[i] == leaf[leaf.size() - i - 1])
		{
			if(leaf[i] == 1)
				cout << 1 << " " << 2 << '\n';
			else
				cout << leaf[i] << " " << leaf[i] - 1 << '\n';
		}
		else
			cout << leaf[i] << " " << leaf[leaf.size() - i - 1] << '\n';
	}
}

/*
6
1 2
2 3
2 4
5 4
6 4
*/

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:46:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   46 |  for(int i = 0; i < (leaf.size() + 1) / 2; i ++)
      |                 ~~^~~~~~~~~~~~~~~~~~~~~~~

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