Submission #765455

#	Time	Username	Problem	Language	Result	Execution time	Memory
765455		vjudge1	Network (BOI15_net)	C++17	100 / 100	398 ms	42312 KiB

net

#include <bits/stdc++.h>
#define int long long
#define ull unsigned long long
#define mps make_pair
#define pb push_back
#define pf push_front
#define F first
#define S second
#define sz(x) (x).size() 
#define all(x) (x).begin(), (x).end()
#define booster ios_base::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define fopen(s) freopen(s".in","r",stdin);freopen(s".out","w",stdout)
 
using namespace std;

const int N = 5e5 + 123;

int n;

vector <int> v,g[N];

vector <pair<int,int>> pr;

bool used[N];

void dfs(int to){
    used[to] = true;
	if(sz(g[to]) == 1){
		v.pb(to);
	}

	for(auto i : g[to]){
		if(!used[i]){
			dfs(i);
		}
	}
}

signed main()
{ 
	booster

	cin >> n;

	for(int i = 1; i <= n - 1; i++)	{
		int x,y;
		cin >> x >> y;

		g[x].pb(y);
		g[y].pb(x);
	}	

	dfs(1);

	cout << (sz(v) + (sz(v) % 2)) / 2 << '\n';

	for(int i = 0; i < sz(v) / 2; i++){
		cout << v[i] << ' ' << v[i + sz(v) / 2] << '\n';
	}

	if(sz(v) % 2 == 1){
		cout << v[0] << ' ' << v[sz(v) - 1] << '\n';
	}

	return 0;
}
/*

1 2 3 4 5 
0 1 2 3 4

*/

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:57:19: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<long long int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   57 |  for(int i = 0; i < sz(v) / 2; i++){
      |                 ~~^~~~~~~~~~~

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