Submission #940077

#	Time	Username	Problem	Language	Result	Execution time	Memory
940077		Baizho	Network (BOI15_net)	C++14	100 / 100	381 ms	42448 KiB

net

#include <bits/stdc++.h>
using namespace std;
#include <ext/pb_ds/assoc_container.hpp>
#include <ext/pb_ds/tree_policy.hpp>
using namespace __gnu_pbds;
  
#define ordered_set tree<int, null_type,less_equal<int>, rb_tree_tag,tree_order_statistics_node_update>
 
 #pragma GCC optimize("Ofast,unroll-loops,fast-math")
 #pragma GCC target("popcnt,avx2")
 
 
typedef long long ll;
typedef unsigned long long ull;
typedef long double ld;
typedef pair<ll,ll> pll;
 
#define sz size()
#define ff first
#define ss second
#define all(a) a.begin(),a.end()
#define pb push_back
 
const int mod = ll(1e9)+7; //(b + (a%b)) % b (to mod -1%(10^9+7) correctly in c++ its -1 but its suppose to be 10^9+6
const ll MOD = 998244353;  // (a%mod)*(binpow(b,mod-2,mod) = (a/b)%mod
const int N = ll(5e5)+100;
const int M = ll(2e5) + 100;
const long long inf = 2e18;
//const long double eps = 1e-15L;
 
ll lcm(ll a, ll b) { return (a / __gcd(a,b))*b; }
 
ll binpow(ll a, ll b, ll m) { ll res=1; a %= m; while(b>0){ if(b&1)res=(res * a) % m; a=(a * a) % m; b/=2; } return res%m;}
 
void Freopen(string Key){ freopen((Key+".in").c_str(), "r", stdin); freopen((Key+".out").c_str(), "w", stdout); }

int n;
vector<int> g[N];
vector<int> leaf;

void dfs(int v, int p = 0) {
	if(g[v].size() == 1) leaf.pb(v);
	for(auto to : g[v]) {
		if(to == p) continue;
		dfs(to, v);
	}
}

void Baizho() {
	cin>>n;
	for(int i = 1; i <= n - 1; i ++) {
		int a, b; cin>>a>>b;
		g[a].pb(b);
		g[b].pb(a);
	}
	dfs(1);
	int m = leaf.size();
	cout<<(m + 1) / 2<<"\n";
	for(int i = 0; i < (m + 1) / 2; i ++) {
		cout<<leaf[i]<<" "<<leaf[i + m / 2]<<"\n";
	}
}
 
signed main() {		
// 	Freopen("nondec");
    ios_base::sync_with_stdio(false);   
    cin.tie(0);cout.tie(0); 
//   	precalc();
   	
    int ttt = 1;
//    cin>>ttt;
 
    for(int i=1; i<=ttt; i++) {Baizho(); }
}

Compilation message (stderr)

net.cpp: In function 'void Freopen(std::string)':
net.cpp:35:34: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   35 | void Freopen(string Key){ freopen((Key+".in").c_str(), "r", stdin); freopen((Key+".out").c_str(), "w", stdout); }
      |                           ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
net.cpp:35:76: warning: ignoring return value of 'FILE* freopen(const char*, const char*, FILE*)' declared with attribute 'warn_unused_result' [-Wunused-result]
   35 | void Freopen(string Key){ freopen((Key+".in").c_str(), "r", stdin); freopen((Key+".out").c_str(), "w", stdout); }
      |                                                                     ~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

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