void process(IEnumerable<int> source, ICollection<int> target1, ICollection<int> target2)
{
  foreach (var i in source)
  {
    if (i % 2 == 0) target1.Add(i)
    else target2.Add(i);
  }
}

K>void process(IEnumerable<int> source, ICollection<int> target1, ICollection<int> target2)
K>{
K>  foreach (var i in source)
K>  {
K>    if (i % 2 == 0) target1.Add(i)
K>    else target2.Add(i);
K>  }
K>}
K>

#include <iterator>
#include <iostream>
#include <sstream>
#include <vector>
#include <list>
#include <set>


template< typename InputIteratorType
        , typename OutputIteratorType1
        , typename OutputIteratorType2
        , typename PredType
        >
void process(InputIteratorType b, InputIteratorType e, OutputIteratorType1 o1, OutputIteratorType2 o2, PredType pred)
{
    for(; b!=e; ++b)
    {
       if (pred(*b))
           *o1++ = *b;
       else
           *o2++ = *b;
    }
}

// Если прям хочется контейнер, то:
template< typename ContainerType
        , typename OutputIteratorType1
        , typename OutputIteratorType2
        , typename PredType
        >
void process(const ContainerType &c, OutputIteratorType1 o1, OutputIteratorType2 o2, PredType pred)
{
    for(const auto &v : c)
    {
       if (pred(v))
           *o1++ = v;
       else
           *o2++ = v;
    }
}

template<typename StreamType, typename ContainerType>
StreamType & printContainer(StreamType &s, const ContainerType &c)
{
    for(const auto &v : c)
        s << v << ", ";
    return s;
}

int main()
{
    std::vector<int> v = { 1, 2, 3, 4, 5, 6, 7, 8};
    std::set<int>  s;
    std::list<int> l;

    process( v, std::inserter(s, s.end()), std::inserter(l, l.end())
           , [](auto v) { return (v % 2 == 0); }
           );

    std::ostringstream oss;
    oss << "Vector: "; printContainer(oss, v) << "\n"; 
    oss << "Set   : "; printContainer(oss, s) << "\n"; 
    oss << "List  : "; printContainer(oss, l) << "\n"; 
 
    std::cout << oss.str();

    return 0;

}

Vector: 1, 2, 3, 4, 5, 6, 7, 8, 
Set   : 2, 4, 6, 8, 
List  : 1, 3, 5, 7,

K>Пишу

template<class T>
void ProcessItems(T itBegin, T itEnd)
{
  while(itBegin != itEnd)
  {
     std::cout << *itBegin++ << ' ';
  }
  std::cout << '\n';
} 


template<class T>
void Process(T& items)
{
    ProcessItems(items.begin(), items.end()); 
}


//...
    std::vector<int> v;
    v.push_back(1);
    v.push_back(2);
    v.push_back(3);

    std::list<int> l;
    l.push_back(1);
    l.push_back(2);
    l.push_back(3);
    l.push_back(5);

    process(v);
    process(l);