Question

What basically I am doing is the set cover problem, removing duplicate from the vectors that has the same numbers. An example:

I have the following vectors of vectors after sorting:

{{1,2,3,4,5},{2,3,7,8},{10,11,12}}

NOW, I would like to remove the occurrence from 2nd vector which is 2,3 and sort again …

 {{1,2,3,4,5},{10,11,12},{7,8}}

I have implemented some code to sort the vectors of vectors but i have problem removing the occurrences from the vector that has less size?

The sort function:

sort(ROWS.begin(),ROWS.end(),VectorsSort());

Thanks for the help.

Answer 1

Pick this apart and take what you need:

#include <algorithm>
#include <vector>

struct binary_search_pred
{
    typedef bool result_type;

    explicit binary_search_pred(std::vector<int> const& v) : v_(&v) { }

    bool operator ()(int const& i) const
    {
        return std::binary_search(v_->begin(), v_->end(), i);
    }

private:
    std::vector<int> const* v_;
};

struct size_comparison_desc
{
    typedef bool result_type;

    typedef std::vector<int> const& arg_t;
    bool operator ()(arg_t a, arg_t b) const
    {
        return b.size() < a.size();
    }
};

void set_cover(std::vector<std::vector<int> >& vec)
{
    typedef std::vector<std::vector<int> > vec_t;
    typedef vec_t::iterator iter_t;
    typedef vec_t::const_iterator citer_t;

    if (vec.empty() || vec.size() == 1)
        return;

    for (iter_t v = vec.begin() + 1, v_end = vec.end(); v != v_end; ++v)
        for (citer_t p = vec.begin(); p != v; ++p)
            v->erase(
                std::remove_if(v->begin(), v->end(), binary_search_pred(*p)),
                v->end()
            );
    std::sort(vec.begin(), vec.end(), size_comparison_desc());
}

(Note that set_cover requires that the contained std::vector<int>s given must already be sorted.)

---

EDIT #1:

As requested in now-deleted comments, a version oriented around std::map<int, std::vector<int>> instead of std::vector<std::vector<int>> (use binary_search_pred from the original code):

#include <algorithm>
#include <map>
#include <vector>

void set_cover(std::map<int, std::vector<int> >& m)
{
    typedef std::map<int, std::vector<int> > map_t;
    typedef map_t::iterator iter_t;
    typedef map_t::const_iterator citer_t;

    if (m.empty() || m.size() == 1)
        return;

    for (iter_t v = ++m.begin(), v_end = m.end(); v != v_end; ++v)
        for (citer_t p = m.begin(); p != v; ++p)
            v->second.erase(
                std::remove_if(
                    v->second.begin(),
                    v->second.end(),
                    binary_search_pred(p->second)
                ),
                v->second.end()
            );
}

Note that the map here will always be sorted by its key, never by the contained vector‘s size (which is what you appear to want). Maybe you want a std::vector<std::pair<int, std::vector<int>>> instead?

---

EDIT #2:

As requested in now-deleted comments, a version oriented around std::vector<std::pair<int, std::vector<int>>> instead of std::map<int, std::vector<int>> (use binary_search_pred from the original code):

#include <algorithm>
#include <utility>
#include <vector>

struct size_comparison_desc
{
    typedef bool result_type;

    typedef std::pair<int, std::vector<int> > const& arg_t;
    bool operator ()(arg_t a, arg_t b) const
    {
        return b.second.size() < a.second.size();
    }
};

void set_cover(std::vector<std::pair<int, std::vector<int> > >& vec)
{
    typedef std::vector<std::pair<int, std::vector<int> > > vec_t;
    typedef vec_t::iterator iter_t;
    typedef vec_t::const_iterator citer_t;

    if (vec.empty() || vec.size() == 1)
        return;

    for (iter_t v = vec.begin() + 1, v_end = vec.end(); v != v_end; ++v)
        for (citer_t p = vec.begin(); p != v; ++p)
            v->second.erase(
                std::remove_if(
                    v->second.begin(),
                    v->second.end(),
                    binary_search_pred(p->second)
                ),
                v->second.end()
            );
    std::sort(vec.begin(), vec.end(), size_comparison_desc());
}