Submission #638409

#	Time	Username	Problem	Language	Result	Execution time	Memory
638409		xad	Network (BOI15_net)	C++17	0 / 100	1 ms	336 KiB

net

#include <bits/stdc++.h>
using namespace std ;
#define nn "\n"
#define x_x ios_base::sync_with_stdio(0);cin.tie(0);cout.tie(0);
#define intt int t; cin>>t; while(t--)
#define emp emplace_back
#define mod 1000000007
#define all(v) v.begin(), v.end()
#define sz(x) (int)x.size()
//#define a first
//#define b second
typedef long long ll;


int main()
{

    x_x
int n; cin>>n; vector<int>adj[n+2]; vector<pair<int,int>>v,ch; int p[n+2];
for(int i=1,x,y; i<n; i++)cin>>x>>y, adj[x].emp(y), adj[y].emp(x),p[x]=y,p[y]=x;
for(int i=1; i<=n; i++)
    if(sz(adj[i])==1)
    {
        ch.push_back({p[i],i});
    }

sort(all(ch));


vector<int>df;
for(int i=0; i<sz(ch)-1; i++)
{
   if(ch[i].first!=ch[i+1].first)
   {
       if(!df.empty()&&df.back()==ch[i].second)df.pop_back();
       df.emp(ch[i].second), df.emp(ch[i+1].second);
       ch[i].first=0;
       if(i==(sz(ch)-2))ch[i+1].first=0;
   }
   else if(!df.empty()&&df.back()==ch[i].second)ch[i].first=0;
}

for(int i=0; i<sz(df)-1; i+=2)v.push_back({df[i],df[i+1]});

 if(sz(df)%2)//v.push_back({df[0],df.back()});
 {
     for(auto&i:ch)
     {
         if(i.second==df.back()){i.first=1; break;}
     }
 }

 int c=0;
 for(int i=0,j=0; i<sz(ch); i++)
{
    if(!ch[i].first)continue;

    while(c!=-1&&(!ch[j].first||i==j))
    { if(c==sz(ch)){c=-1; break;} j=(j+1)%sz(ch); ++c;}

if(c==-1)
    {if(i==j)j=(j+1)%sz(ch); }
else c=0;
  v.push_back({ch[i].second,ch[j].second}), ch[j].first=0;

  ch[i].first=0;
}

 cout<<sz(v)<<nn;

for(auto i:v)cout<<i.first<< ' '<<i.second<<nn;


return 0;
}

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