제출 #24942

#	제출 시각	아이디	문제	언어	결과	실행 시간	메모리
24942		RezwanArefin01	Network (BOI15_net)	C++14	0 / 100	0 ms	13736 KiB

net

//Bismillahir Rahmanir Rahim
#include <bits/stdc++.h>
using namespace std;
typedef long long ll;
typedef pair<int,int> ii;
const int maxn = 5e5;
vector<int> adj[maxn], lef; 
void dfs(int u, int par){
	int cnt = 0;
	for(int v : adj[u]) if(v - par){
		cnt++, dfs(v, u); 
	} 
	if(!cnt) lef.push_back(u);
}
int main(int argc, char const *argv[]) {
#ifdef LOCAL_TESTING
	freopen("in", "r", stdin);
#endif
	int n; cin>>n; 
	for(int i=0; i<n-1; i++) {
		int u, v; 
		cin>>u>>v;
		adj[u].push_back(v); 
		adj[v].push_back(u); 
	}
	for(int i=1; i<=n; i++) if(adj[i].size() > 1) {
		dfs(i, 0); break;
	}
	int sz = int((lef.size()+1)/2); 
	cout<<sz<<endl;
	for(int i=0; i<sz; i++) {
		cout<<lef[i]<<" " << lef[i + sz/2]<<endl;
	}
} 

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