Submission #940120

#	Time	Username	Problem	Language	Result	Execution time	Memory
940120		vjudge1	Network (BOI15_net)	C++17	100 / 100	356 ms	46168 KiB

net

// in the name of God
#include<bits/stdc++.h>
using namespace std;
#define int long long
#define fast() ios::sync_with_stdio(0); cin.tie(0); cout.tie(0);
#define ff first
#define ss second
#define pb(x) push_back(x)
#define all(x) x.begin(), x.end()
#define mk make_pair
#define ppb pop_back
#define endl '\n'
#define pii pair<int, int>
#define sz(x) (int)x.size()
#define file() freopen("input.txt", "r", stdin);
#pragma GCC optimize("Ofast")
#pragma GCC optimize("O4")
#pragma GCC optimize("unroll-loops")
//#pragma GCC target("avx2")
mt19937 rng(chrono::steady_clock::now().time_since_epoch().count());
const int mod = 1e9 + 7, maxn = 5e5 + 10, sq = 3163, inf = 1e18 + 10, lg = 25, pp = 4447, modd = 1e9 + 9;

int n;
vector<vector<int>> g(maxn);
vector<int> b;

void dfs(int u = 0, int par = -1){
	if(g[u].size() == 1) b.pb(u);
	for(int v : g[u]){
		if(v != par) dfs(v, u);
	}
}
signed main(){
	fast();//file();
	cin >> n;
	for(int i = 1; i < n; ++i){
		int u, v; cin >> u >> v;
		u--; v--;
		g[v].pb(u);
		g[u].pb(v);
	}
	dfs();
	int ans = b.size() + 1;
	ans /= 2;
	cout << ans << endl;
	for(int i = 0; i < (b.size() - (b.size() / 2)); ++i){
		cout << b[i] + 1 << " " << b[i + (b.size() / 2)] + 1 << endl;
	}
}
// Happiness can be found even in the darkest of times,
// if one only remembers to turn on the light.

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:46:19: 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]
   46 |  for(int i = 0; i < (b.size() - (b.size() / 2)); ++i){
      |                 ~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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