Submission #639445

#	Time	Username	Problem	Language	Result	Execution time	Memory
639445		zordeno	Network (BOI15_net)	C++17	0 / 100	8 ms	15956 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);

	vector <ll> frq(MAX);
	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);
		frq[u]++, frq[v]++;
	}
	ll sum = 0, prv;
	for (ll i = 0; i < n; i++)
	{
		if (frq[i] < 2)
		{
			sum++;
		}
	}
	cout << ceil(sum * 1.0 / 2.0) << endl;
	sum = 0;
	for (ll i = 0; i < n; i++)
	{
		if (frq[i] < 2)
		{
			sum++;
			if (sum % 2 == 0)
			{
				cout << prv + 1 << " " << i + 1 << endl;
				adj[prv].push_back(i);
				adj[i].push_back(prv);
			}
			prv = i;
		}
	}
	if (sum % 2 != 0)
	{
		for (ll i = n - 1; i >= 0; i--)
		{
			if (frq[i] < 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;
						return 0;
					}
				}
			}
		}
	}
}

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