#include <set>
#include <vector>
#include <functional>
#include <algorithm>

// take a set of values and pairs them up at random, without repeats.
template < typename T >
std::vector< std::pair<T,T> > make_unique_pairs( const std::set<T>& set )
{
    std::vector< std::pair<T,T> > result ;

    // make a vector of references to elements in the set
    std::vector< std::reference_wrapper< const T > > seq( set.begin(), set.end() ) ;

    // make a random permutation of the references
    std::random_shuffle( std::begin(seq), std::end(seq) ) ;

    // make pairs and place them into the result
    for( std::size_t i = 0 ; i < seq.size() - 1 ; i += 2 )
        result.emplace_back( seq[i], seq[i+1] ) ;

    return result ;
}

#include <cstdlib>
#include <ctime>
#include <iostream>

int main()
{
    std::srand( std::time(nullptr) ) ;

    const std::set<int> values { 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15 } ;

    for( auto pair : make_unique_pairs(values) )
        std::cout << pair.first << ',' << pair.second << '\n' ;
}