Submission #748426

#	Time	Username	Problem	Language	Result	Execution time	Memory
748426		mariowong	Network (BOI15_net)	C++14	100 / 100	514 ms	50136 KiB

net

#include <bits/stdc++.h>
using namespace std;

int deg[500005]; 
vector <int> edge[500005]; 
bool vis[500005];
vector <int> v;
void dfs(int x){
	vis[x]=true;
	if (deg[x] == 1) v.push_back(x);
	for (int i=0;i<edge[x].size();i++){
		if (!vis[edge[x][i]]) dfs(edge[x][i]);
	}
}
int main(){
	ios::sync_with_stdio(false); 
	int n;
	cin >> n;
	for (int i=1;i<n;i++){
		int u,v;
		cin >> u >> v;
		edge[u].push_back(v);
		edge[v].push_back(u); 
		deg[u]++; deg[v]++;
	}	
	int cnt=0;
	for (int i=1;i<=n;i++){
		if (deg[i] == 1) cnt++;
	}
	cout << (cnt+1)/2 << "\n";
	for (int i=1;i<=n;i++){
		if (deg[i] > 1){
			dfs(i);
			break;	
		}
	}
	if (cnt%2 == 1) v.push_back(v[(int)v.size()-1]);
	for (int i=0;i+(cnt+1)/2<v.size();i++){
		cout << v[i] << " " << v[i+(cnt+1)/2] << "\n";
	}
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int)':
net.cpp:11:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   11 |  for (int i=0;i<edge[x].size();i++){
      |               ~^~~~~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:38:26: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   38 |  for (int i=0;i+(cnt+1)/2<v.size();i++){
      |               ~~~~~~~~~~~^~~~~~~~~

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