Submission #260011

#	Time	Username	Problem	Language	Result	Execution time	Memory
260011		test2	Network (BOI15_net)	C++14	0 / 100	2 ms	2688 KiB

net

#include<bits/stdc++.h>

using namespace std ; 
using ll = long long ; 

const int N =1e5 + 7 ; 

int n ; 

vector<int> adj[N] ;
vector<pair<int , int> > ans ;

int dfs(int x , int p){

	int ls = 0; 
	vector<int> chs ;	
	for(auto u : adj[x]){
		if(u == p)
			continue ; 
		chs.push_back(dfs(u , x)) ;
	}

	while(chs.size() > 1){
		ls = chs.back() ; 
		int u = chs.back() ; chs.pop_back() ; 
		int v = chs.back() ;chs.pop_back() ;
		ans.push_back({u , v}) ; 
	}

	if(x == 1 && chs.size()){
		ans.push_back({x , chs.back() }) ;
	}	

	if(chs.size())
		return chs.back() ;

	if(ls)return ls ; 

	return x ; 
}


int main(){

	ios_base::sync_with_stdio(0) ; 
	cin.tie(0) ; 
	//freopen("in.in" , "r" , stdin) ; 

	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) ; 
	}

	dfs(1 , 1) ; 


	cout<< ans .size() <<"\n" ; 
	for(auto u : ans){
		cout<< u.first<<" " << u.second <<"\n" ; 
	}

	return 0 ; 
}

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