Submission #639447

#	Time	Username	Problem	Language	Result	Execution time	Memory
639447		zordeno	Network (BOI15_net)	C++17	0 / 100	7 ms	12056 KiB

net

#include <bits/stdc++.h>

using namespace std;
#define     endl            '\n'
#define     ll              long long

const ll MOD = 1e9 + 7, MAX = 5e5 + 5, INF = 1e18;

vector <int> dx = { 1, 0, 0, -1, 1, 1, -1, -1 };
vector <int> dy = { 0, 1, -1, 0, -1, 1, 1, -1 };

ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll lcm(ll a, ll b) { return (a / gcd(a, b)) * b; }

vector <ll> adj[MAX];
int main()
{
    ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
    //freopen("", "r", stdin);
    //freopen("", "w", stdout);

	ll n;
	cin >> n;
	for (ll i = 0; i < n - 1; i++)
	{
		ll u, v;
		cin >> u >> v;
		u--, v--;
		adj[u].push_back(v);
		adj[v].push_back(u);
	}
	ll sum = 0, prv;
	for (ll i = 0; i < n; i++)
	{
		if (adj[i].size() < 2)
		{
			sum++;
		}
	}
	cout << ceil(sum * 1.0 / 2.0) << endl;
	vector <ll> ans;
	for (ll i = 0; i < n; i++)
	{
		if (adj[i].size() < 2)
		{
			ans.push_back(i);
		}
	}
	for (ll i = 0; i < ans.size() - 1; i += 2)
	{
		cout << ans[i] + 1 << " " << ans[i + 1] + 1 << endl;
		adj[ans[i]].push_back(ans[i + 1]);
		adj[ans[i + 1]].push_back(ans[i]);
	}
	if (ans.size() % 2 != 0)
	{
		for (ll i = n - 1; i >= 0; i--)
		{
			if (adj[i].size() < 2)
			{
				for (ll j = 0; j < n; j++)
				{
					bool flag = 0;
					for (auto child : adj[i])
					{
						if (child == j)
						{
							flag = 1;
							break;
						}
					}
					if (!flag)
					{
						cout << i + 1 << " " << j + 1 << endl;
						break;
					}
				}
			}
		}
	}
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:49:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   49 |  for (ll i = 0; i < ans.size() - 1; i += 2)
      |                 ~~^~~~~~~~~~~~~~~~
net.cpp:32:14: warning: unused variable 'prv' [-Wunused-variable]
   32 |  ll sum = 0, prv;
      |              ^~~

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