Submission #346761

#	Time	Username	Problem	Language	Result	Execution time	Memory
346761		alishahali1382	Network (BOI15_net)	C++14	100 / 100	537 ms	60544 KiB

net

#include <bits/stdc++.h>
#pragma GCC optimize ("O2,unroll-loops")
//#pragma GCC optimize("no-stack-protector,fast-math")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

using namespace std;
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<pii, int> piii;
typedef pair<ll, ll> pll;
#define debug(x) cerr<<#x<<'='<<(x)<<endl;
#define debugp(x) cerr<<#x<<"= {"<<(x.first)<<", "<<(x.second)<<"}"<<endl;
#define debug2(x, y) cerr<<"{"<<#x<<", "<<#y<<"} = {"<<(x)<<", "<<(y)<<"}"<<endl;
#define debugv(v) {cerr<<#v<<" : ";for (auto x:v) cerr<<x<<' ';cerr<<endl;}
#define all(x) x.begin(), x.end()
#define pb push_back
#define kill(x) return cout<<x<<'\n', 0;

const int inf=1000000010;
const ll INF=10000000000000010LL;
const int mod=1000000007;
const int MAXN=500010, LOG=20;

int n, m, k, u, v, x, y, t, a, b, root;
int A[MAXN];
vector<int> G[MAXN], vec;
vector<pii> out;

void dfs(int node, int par){
	if (G[node].size()==1) vec.pb(node);
	for (int v:G[node]) if (v!=par) dfs(v, node);
}

int main(){
	ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);
	cin>>n;
	for (int i=1; i<n; i++){
		cin>>u>>v;
		G[u].pb(v);
		G[v].pb(u);
	}
	for (int i=1; i<=n; i++) if (G[i].size()>1) root=i;
	dfs(root, 0);
	if (vec.size()%2) vec.pb(root);
	int sz=vec.size()/2;
	for (int i=0; i<sz; i++) out.pb({vec[i], vec[i+sz]});
	cout<<out.size()<<"\n";
	for (pii p:out) cout<<p.first<<" "<<p.second<<"\n";
	
	return 0;
}
/*
8
1 2
2 3
3 4
4 5
3 6
3 7
3 8
*/

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