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

Question

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

Answer 1

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.

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

      typename std::vector::const_iterator ii = i;
      for (typename std::vector::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.)