Submission #923294

#	Time	Username	Problem	Language	Result	Execution time	Memory
923294		Aiperiii	Network (BOI15_net)	C++14	100 / 100	539 ms	48612 KiB

net

#include <bits/stdc++.h>
#define int long long
#define ff first
#define ss second
#define pb push_back
#define all(x) x.begin(),x.end()
using namespace std;
const int N=5e5+5;
vector <int> g[N];
vector <int> lf;
void dfs(int v,int p){
   if(g[v].size()==1)lf.pb(v);
   for(auto to : g[v]){
      if(to!=p){
         dfs(to,v);
      }
   }
}
signed main(){
   ios_base::sync_with_stdio();
   cin.tie(0);cout.tie(0);
   int n;cin>>n;
   for(int i=0;i<n-1;i++){
      int u,v;
      cin>>u>>v;
      g[u].pb(v);
      g[v].pb(u);
   }
   
   dfs(1,0);
   cout<<(lf.size()+1)/2<<"\n";
   for(int i=0;i<(lf.size()+1)/2;i++){
      cout<<lf[i]<<" "<<lf[i+lf.size()/2]<<"\n";
   }
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:32:17: 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]
   32 |    for(int i=0;i<(lf.size()+1)/2;i++){
      |                ~^~~~~~~~~~~~~~~~

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