объединение множеств

template<class ValType, class FwdIt>
  FwdIt copy ( FwdIt first, FwdIt last, FwdIt result )
{
  while (first!=last) *result++ = *first++;
  return result;
}
 
template <class ValType, class FwdIt>
FwdIt set_union(FwdIt first1, FwdIt last1, 
                FwdIt first2, FwdIt last2, FwdIt result)
{
    merge_sort<ValType, FwdIt>(first1, last1);
    merge_sort<ValType, FwdIt>(first2, last2);
    while (true)
    {
        if (first1==last1) return copy<ValType, FwdIt>(first2,last2,result);
        if (first2==last2) return copy<ValType, FwdIt>(first1,last1,result);
 
        if (*first1<*first2) *result++ = *first1++;
        else if (*first2<*first1) *result++ = *first2++;
        else { *result++ = *first1++; first2++; }
    }
}

int main()
{   
    char s[7] = {'A','B','F','D','A','F','F'}; // check set_union
    char q[6] = {'E','A', 'B','H','F','C'};
    char result[10];
    set_union<char>(s,s + 6, q, q + 5, result);
    int size_r = strlen(result);
    for(int i = 0; i < size_r; i++)
        cout << result[i] << ' ';
    cout << endl;
 
 
    return 0;
}

set_union<char>(s,s + 7, q, q + 6, result);

template <class ValType, class FwdIt> void merge(FwdIt first, FwdIt middle, FwdIt last, ValType *arr)
{
 
    int cursor = 0;
 
    FwdIt f = first, center = middle;
 
    while(first != middle && center != last)
        if(*first < *center)
            arr[cursor++] = *(first++);
        else
            arr[cursor++] = *(center++);
        
    
    while(first != middle)
        arr[cursor++] = *(first++);       
  
    while(center != last)
        arr[cursor++] = *(center++);    
    
 
    for(int i = 0; i < cursor; i++, f++)
        *f = arr[i];
}
template <class ValType, class FwdIt> void merge_sort(FwdIt first, FwdIt last)
{
    int n = last - first;
    ValType *arr = new ValType[n];
 
 
    if(n > 1){
        FwdIt mid = first + (n / 2);
        merge_sort<ValType, FwdIt>(first, mid);
        merge_sort<ValType, FwdIt>(mid, last);
        merge<ValType, FwdIt>(first, mid, last, arr);
    }
    delete[] arr;
}