Submission #394748

#	Time	Username	Problem	Language	Result	Execution time	Memory
394748		Saynaa	Network (BOI15_net)	C++17	0 / 100	7 ms	12064 KiB

net

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
const int MAXN = 5e5 + 10;
int n;
vector< int > adj[MAXN], ls;

void dfs(int u, int p = -1){
	if( adj[u].size() == 1) ls.push_back(u);
	for(int i = 0; i < adj[u].size(); i ++){
		int v = adj[u][i];
		if( v == p) continue;
		dfs(v, u);
	}
}

int main(){
	ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
	cin >> n;
	for(int i = 1; i < n; i ++){
		int u, v;
		cin >> u >> v, u --, v --;
		adj[u].push_back(v), adj[v].push_back(u);
	}
	dfs(0);
	cout << (ls.size() + 1)/2 << '\n';
	if( ls.size() % 2){
		cout << ls.front() + 1 << " " << ls.back() + 1 << endl;
		ls.pop_back();
	}
	int pt = ls.size() - 1;
	for(int i = 0; i < ls.size()/2; i ++){
		cout  << ls[i] + 1 << " " << ls[pt] + 1 << endl;
		pt --;
	}
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'void dfs(int, int)':
net.cpp:10:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   10 |  for(int i = 0; i < adj[u].size(); i ++){
      |                 ~~^~~~~~~~~~~~~~~
net.cpp: In function 'int main()':
net.cpp:32:19: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   32 |  for(int i = 0; i < ls.size()/2; i ++){
      |                 ~~^~~~~~~~~~~~~

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