Submission #397020

#	Time	Username	Problem	Language	Result	Execution time	Memory
397020		The_Blitz	Network (BOI15_net)	C++17	100 / 100	727 ms	47668 KiB

net

// Restart
// += O(logn) ; + = O(n)
 
//#pragma GCC optimize("Ofast")
//#pragma GCC optimize("unroll-loops")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#include<bits/stdc++.h>
#include <ext/pb_ds/assoc_container.hpp> // Common file
#include <ext/pb_ds/tree_policy.hpp> // Including tree_order_statistics_node_update
 
#define fastio ios_base::sync_with_stdio(0);cin.tie(0)
#define fst first
#define snd second
#define all(x) (x).begin(), (x).end()
#define pb push_back
#define sz size()
#define FORN(i,j,n) for(int i=j; i<(int)n;i++) 
#define FOR(i,n) FORN(i,0,n)
#define FORIT(i,x) for( auto i = x.begin() ; i != x.end() ; i++ )
#define MOD 998244353LL
#define MOD1 1000000007LL
#define LIM 262150
#define ones(x) __builtin_popcount(x)
#define trace(x)    cerr << #x << ": " << x << endl;
#define trace2(x, y) cerr << #x << ": " << x << " | " << #y << ": " << y << endl;
#define trace3(x, y,z) cerr << #x << ": " << x << " | " << #y << ": " << y << " | " << #z << ": " << z << endl;
#define INF 1000000000
#define in(x)  cin>>x;
#define out(x) cout<<x;
#define MAXIMO 1LL<<60

#define loga2(x) __builtin_ctzll(x)
//SOLO PARA POTENCIAS DE 2
 
using namespace std;
using namespace __gnu_pbds;
 
typedef long long ll ;
typedef unsigned long long ull ;
typedef vector <int> vi;
typedef pair <int,int> ii;
typedef pair <int,ii> iii;
typedef vector <string> vs;
typedef vector <ii> vii;
typedef vector <iii> viii;
typedef tree<int,null_type,less<int>,rb_tree_tag,tree_order_statistics_node_update> ordered_set;


vi G[500005];
vi ans;

void dfs(int curr, int ant = -1){
	bool leaf = true;
	for(auto v: G[curr]) {
		if(ant != v){
			dfs(v,curr);
			leaf=false;
		}
	}
	if(leaf) ans.pb(curr);
}

void go(){

	int n; cin>>n;
	
	for(int i=1; i<n;i++){
		int x, y; cin >> x >> y;
		G[x].pb(y);
		G[y].pb(x);
	}
	//Input is a tree
	for(int i=1; i<=n; i++){
		if(G[i].size() != 1){
			dfs(i);
			break;
		}
	}

	cout<< (ans.size() + 1)/2 <<"\n";


	for(int i=0; i< (ans.size()+1)/2; i++){
		cout<<ans[i] << " " << ans[i + ans.size()/2 ]<<"\n";
	}

}


void timer(){
	clock_t begin = clock();
	go();
	clock_t end = clock();
	double time_spent = (double)(end - begin) / CLOCKS_PER_SEC;
	cout<<time_spent<<"\n";
}	

 
int main() {
  //fastio;
  go();
  //timer();
  return 0;
}

Compilation message (stderr)

net.cpp: In function 'void go()':
net.cpp:83:16: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   83 |  for(int i=0; i< (ans.size()+1)/2; i++){
      |               ~^~~~~~~~~~~~~~~~~~

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