Работа функции unique_copy ()

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <iterator>
 
using std :: cout;
using std :: cin;
using std :: string;
using std :: vector;
 
int main () {
    vector <string> matt;
    string temp;
    cout << "Matt's guests:\n";
    std :: ostream_iterator <string>  out (cout, ", ");
    while ( getline (cin, temp) && temp != "quit")
        matt.push_back (temp);
    sort (matt.begin (), matt.end ());
    copy (matt.begin (), matt.end (), out);
    vector <string> patt;
    cout << "Patt's guests:\n";
    while ( getline (cin,temp) && temp != "quit")
        patt.push_back (temp);
    sort (patt.begin (), patt.end ());
    copy (patt.begin (), patt.end (), out);
    vector <string> pred_result;
    vector <string> result;
    merge (matt.begin (), matt.end (), patt.begin (), patt.end (), std :: back_inserter (pred_result));
    unique_copy (pred_result.begin (), pred_result.end (), std :: back_inserter (result));
    copy (result.begin (), result.end (), out);
    cin.ignore (1);
    cin.get ();
    return 0;
};

    vector <string> pred_result;
    vector <string> result;
    merge (matt.begin (), matt.end (), patt.begin (), patt.end (), std :: back_inserter (pred_result));
    unique_copy (pred_result.begin (), pred_result.end (), std :: back_inserter (result));
    std::cout << std::endl;
    std::cout << "unique:\n";
    copy (result.begin (), result.end (), out);

#include <iostream>
#include <algorithm>
#include <string>
#include <iterator>
#include <set>
 
using namespace std;
 
int main ()
{
    string temp;
    using ois = ostream_iterator<string>;
 
    set<string> matt;
    cout << "Enter Matt's guests:\n";
    while ( getline(cin, temp) && temp != "quit" )
        matt.insert(temp);
 
    cout << "Matt's guests:\n";
    copy( begin(matt), end(matt), ois(cout, ", "));
 
    set<string> patt;
    cout << "\nEnter Patt's guests:\n";
    while ( getline(cin, temp) && temp != "quit" )
        patt.insert(temp);
 
    cout << "\nPatt's guests:\n";
    copy( begin(patt), end(patt), ois(cout, ", "));
 
    set<string> result;
    merge( begin(matt), end(matt), begin(patt), end(patt),
                inserter(result, begin(result)) );
 
    std::cout << "\nUnique:\n";
    copy( begin(result), end(result), ois(cout, ", "));
    cin.get ();
    return 0;
};