1121. Damn Single (25)

#include <iostream>
#include <vector>
#include <cstdio>
#include <algorithm>
#include <map>
using namespace std;
vector<int> dsv,guests;
map<int,int> couples;
map<int,bool> ishere;
int main()
{
int n,m;
cin>>n;
for(int i=0;i<n;++i)
{
int id1,id2;
cin>>id1>>id2;
ishere[id1]=false;
ishere[id2]=false;
couples[id1]=id2;
couples[id2]=id1;
}
cin>>m;
guests.resize(m);
for(int i=0;i<m;++i)
{
cin>>guests[i];
ishere[guests[i]]=true;
}
for(auto id:guests)
{
if(!(couples.count(id)&&ishere[couples[id]])) dsv.push_back(id);
}
sort(dsv.begin(),dsv.end());
cout<<dsv.size()<<endl;
for(unsigned int i=0;i<dsv.size();++i) i==dsv.size()-1?printf("%05d",dsv[i]):printf("%05d ",dsv[i]);
return 0;
}