Submission #614159

#	Time	Username	Problem	Language	Result	Execution time	Memory
614159		sword060	Network (BOI15_net)	C++17	100 / 100	596 ms	69416 KiB

net

#include <bits/stdc++.h>
using namespace std;
int x;
vector<int>v[500005];
vector<pair<int,int>>ans;
vector<int> dfs(int i,int p=-1){
  vector<int>ret;
  if(v[i].size()==1)ret.push_back(i);
  for(auto j:v[i]){
    if(j==p)continue;
    vector<int>lol=dfs(j,i);
    if(lol.size()>ret.size())swap(lol,ret);
    while(ret.size()&&ret.size()+lol.size()>2){
      int c1=ret.back(),c2=lol.back();
      ret.pop_back();lol.pop_back();
      ans.push_back({c1,c2});
    }
    for(auto k:lol)ret.push_back(k);
  }
  if(p==-1){
    for(int j=0;j<ret.size()/2;j++)
      ans.push_back({ret[j],ret[ret.size()-j-1]});
    if((int)ret.size()%2)ans.push_back({ret[ret.size()/2],i});
  }
  return ret;
}
int main(){
  ios::sync_with_stdio(0); cin.tie(0);
  cin>>x;
  for(int i=1;i<=x-1;i++){
    int l,r;cin>>l>>r;
    v[l].push_back(r);
    v[r].push_back(l);
  }
  for(int i=1;i<=x;i++)if(v[i].size()>1){dfs(1);break;}
  cout<<ans.size()<<"\n";
  for(auto [l,r]:ans)cout<<l<<" "<<r<<endl;
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'std::vector<int> dfs(int, int)':
net.cpp:21:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   21 |     for(int j=0;j<ret.size()/2;j++)
      |                 ~^~~~~~~~~~~~~

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