Function problem_14

examples/99_problems.cpp:131–134

P14 (*) Duplicate the elements of a list.

// P14 (*) Duplicate the elements of a list.
void problem_14()
{
    print_result(replicate_elems(2, xs));
}

// P15 (**) Replicate the elements of a list a given number of times.
void problem_15()