How to check whether a vector is a subset of another in c++

I am trying to find a simple way to check whether a vector is a subset of another without sorting 开发者_开发问答the order of elements in the vector. Both the vectors contain random number elements in them.

std::includes seems to work only for sorted ranges. How can I accomplish this?

Copy the vectors. Sort the copies. Then use std::includes on the copies.

template <typename T>
bool IsSubset(std::vector<T> A, std::vector<T> B)
{
    std::sort(A.begin(), A.end());
    std::sort(B.begin(), B.end());
    return std::includes(A.begin(), A.end(), B.begin(), B.end());
}

My answer assumes that when you say "subset", you are really searching more for the equivalent of a "substring"; that is, maintaining order of elements during the search.

Ultimately, I can't see how you could do this in anything less than O(n*m). Given that, you can just roll your own pretty simply:

template <typename T1, typename T2>
bool contains(std::vector<T1> const& a, std::vector<T2> const& b) {
   for (typename std::vector<T1>::const_iterator i = a.begin(), y = a.end(); i != y; ++i) {
      bool match = true;

      typename std::vector<T1>::const_iterator ii = i;
      for (typename std::vector<T2>::const_iterator j = b.begin(), z = b.end(); j != z; ++j) {
          if (ii == a.end() || *j != *ii) {
              match = false;
              break;
          }
          ii++;
      }

      if (match)
         return true;
   }

   return false;
}

Live demo.

(You could probably be more creative with the template parameters.)

This is assuming duplicates do NOT matter. So if you have two instances of the number 99 in vector a, then as long as vector b has at least one instance of the number 99, then it will be declared as a subset.

bool isSubset(const std::vector<int>& a, const std::vector<int>& b)
{
    for (std::vector<int>::const_iterator i = a.begin(); i != a.end(); i++)
    {
        bool found = false;

        for (std::vector<int>::const_iterator j = b.begin(); j != b.end(); j++)
        {
            if (*i == *j)
            {
                found = true;
                break;
            }
        }

        if (!found)
        {
            return false;
        }
    }

    return true;
}

With no sorting...

template <typename T>
bool isSubsetOrEqual(std::vector<T> const& a, std::vector<T> const& b) {
   for(auto const& av:a){
      if(std::find(b.begin(),b.end(),av)==b.end())
          return false;
   }
   return true;
}