Submission #853596

#	Time	Username	Problem	Language	Result	Execution time	Memory
853596		NK_	Network (BOI15_net)	C++17	0 / 100	1 ms	600 KiB

net

// Success consists of going from failure to failure without loss of enthusiasm
#include <bits/stdc++.h>
 
using namespace std;
 
#define nl '\n'
#define pb push_back
#define pf push_front
 
#define mp make_pair
#define f first
#define s second
#define sz(x) int(x.size())
 
template<class T> using V = vector<T>;
using pi = pair<int, int>;
using vi = V<int>;
using vpi = V<pi>;
 
using ll = long long;
using pl = pair<ll, ll>;
using vpl = V<pl>;
using vl = V<ll>;
 
using db = long double;
 
template<class T> using pq = priority_queue<T, V<T>, greater<T>>;
 
const int MOD = 1e9 + 7;
const ll INFL = ll(1e17);
const int LG = 18;

int main() {
	cin.tie(0)->sync_with_stdio(0);

	int N; cin >> N;

	vi deg(N);
	V<vi> adj(N); for(int i = 0; i < N - 1; i++) {
		int u, v; cin >> u >> v; --u, --v;
		adj[u].pb(v);
		adj[v].pb(u);
		deg[u]++, deg[v]++;
	}

	int R = -1; for(int i = 0; i < N; i++) if (deg[i] > 1) R = i;

	vi L;
	function<void(int, int)> dfs = [&](int u, int p) {
		bool leaf = 1;
		for(auto& v : adj[u]) if (v != p) {
			leaf = 0;
			dfs(v, u);
		}

		if (leaf) L.pb(u);
	};

	dfs(R, -1);

	cout << (sz(L) + 1) / 2 << nl;
	for(int i = 0; i < sz(L) / 2; i++) cout << L[i] + 1 << " " << L[sz(L) - 1 - i] + 1 << nl;

	if (sz(L) % 2) {
		cout << L[sz(L) / 2] + 1 << " " << L[0] + 1 << nl;
	}

	exit(0-0);
} 	

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