Submission #614145

#	Time	Username	Problem	Language	Result	Execution time	Memory
614145		sword060	Network (BOI15_net)	C++17	0 / 100	8 ms	12144 KiB

net

#include <bits/stdc++.h>
using namespace std;
int x;
vector<int>v[500005];
vector<pair<int,int>>ans;
set<pair<int,int>> dfs(int i,int aa,int c,int p=-1){
  set<pair<int,int>>ret;
  if(v[i].size()==1)ret.insert({c,i});
  for(auto j:v[i]){
    if(j==p)continue;
    set<pair<int,int>>lol=dfs(j,aa,c+1,i);
    for(auto k:lol)ret.insert({k.first,k.second});
  }
  if(i==aa){
    vector<int>vv;
    for(auto [j,r]:ret)vv.push_back(r);
    for(int j=0;j<vv.size()/2;j++)ans.push_back({vv[j],vv[(int)vv.size()-j-1]});
    if((int)vv.size()%2){
      int m1=vv[vv.size()/2];
      ans.push_back({m1,vv.back()});
    }
  }
  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((int)v[i].size()==1){dfs(i,i,0,i);break;}
  cout<<ans.size()<<"\n";
  for(auto [l,r]:ans)cout<<l<<" "<<r<<endl;
	return 0;
}

Compilation message (stderr)

net.cpp: In function 'std::set<std::pair<int, int> > dfs(int, int, int, int)':
net.cpp:17:18: warning: comparison of integer expressions of different signedness: 'int' and 'std::vector<int>::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   17 |     for(int j=0;j<vv.size()/2;j++)ans.push_back({vv[j],vv[(int)vv.size()-j-1]});
      |                 ~^~~~~~~~~~~~

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