Submission #923267

#	Time	Username	Problem	Language	Result	Execution time	Memory
923267		Aiperiii	Network (BOI15_net)	C++14	0 / 100	4 ms	13872 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];
int d[N];
void dfs(int v,int p){
   for(auto to : g[v]){
      if(to!=p){
         d[to]=d[v]+1;
         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);
   }
   int root=1;
   for(int i=1;i<=n;i++){
      if(g[i].size()==1){
         root=i;
      }
   }
   //cout<<root<<"\n";
   dfs(root,0);
   vector <pair <int,int> > v;
   for(int i=1;i<=n;i++){
      if(g[i].size()==1 && i!=root)v.pb({d[i],i});
   }
   sort(all(v));
   //cout<<v.size()<<"\n";
   cout<<v.size()/2+1<<"\n";
   for(int i=0;i<v.size()-1;i+=2){
      cout<<v[i].ss<<" "<<v[i+1].ss<<"\n";
   }
   cout<<v.back().ss<<" "<<root<<"\n";
}

Compilation message (stderr)

net.cpp: In function 'int main()':
net.cpp:44:17: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::pair<long long int, long long int> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   44 |    for(int i=0;i<v.size()-1;i+=2){
      |                ~^~~~~~~~~~~

• Subtask 1: 0 / 18
• Subtask 2: 0 / 45
• Subtask 3: 0 / 37