Submission #394601

#	Time	Username	Problem	Language	Result	Execution time	Memory
394601		Nima_Naderi	Network (BOI15_net)	C++14	100 / 100	496 ms	55108 KiB

net

//In the name of GOD
#include<bits/stdc++.h>
using namespace std;

typedef long long ll;
const ll MXN = 5e5 + 10;
ll n, rt, lf;
ll d[MXN];
vector<ll> adj[MXN], L;
void dfs(ll u, ll par){
	if(d[u] == 1){
		L.push_back(u), lf ++;
	}
	for(auto v : adj[u]){
		if(v != par) dfs(v, u);
	}
}
int main(){
	ios::sync_with_stdio(0);cin.tie(0); cout.tie(0);
	cin >> n;
	for(int i = 1; i < n; i ++){
		ll u, v; cin >> u >> v; d[u] ++, d[v] ++;
		adj[u].push_back(v), adj[v].push_back(u);
	}
	for(int i = 1; i <= n; i ++) if(d[i] > 1) rt = i;
	dfs(rt, 0);
	cout << (lf + 1) / 2 << '\n';
	for(int i = 0; i < lf - lf / 2; i ++){
		cout << L[i] << ' ' << L[i + lf / 2] << '\n';
	}
	return 0;
}
// N.N_2004
// THIS IS THE PAYOFF

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