匹配两个std :: vectors之间的元素

Question

I am writing a module that estimates optical flow. At each time step it consumes an std::vector where each element of the vector is a current pixel location and a previous pixel location. The vector is not ordered. New pixels that were previously not seen will be present and flow locations that were not found will be gone. Is there a correct way to match elements in the new vector to the set of optical flow locations being estimated?

The vectors are on the order of 2000 elements.

These are the approaches I am considering:

• naively iterate through the new vector for each estimated optical flow location
• naively iterating through the new vector but removing each matched location so the search gets faster as it goes on
• run std::sort on my list and the new list at every time step. Then iterate through the new vector starting at the last matched index +1

I'm suspecting that there is an accepted way to go about this but I don't have any comp sci training.

I'm in c++ 11 if that is relevant.

// each element in the new vector is an int. I need to check if 
// there are matches between the new vec and old vec
void Matcher::matchOpticalFlowNaive(std::vector<int> new_vec)
{
for(int i = 0; i < this->old_vec.size(); i++)
    for(int j =0; j < new_vec.size(); j++)
        if(this->old_vec[i] == new_vec[j]){
            do_stuff(this->old_vec[i],  new_vec[j])
            j = new_vec.size();
        }
}

Answer 1

Not sure to understand what do you need but, supposing that your Matcher is constructed with a vector of integer, that there ins't important the order and that you need check this vector with other vectors (method matchOpticalFlowNaive() ) to do something when there is a match, I suppose you can write something as follows

struct Matcher
 {
   std::set<int> oldSet;

   Matcher (std::vector<int> const & oldVect)
      : oldSet{oldVect.cbegin(), oldVect.cend()}
    { }

   void matchOpticalFlowNaive (std::vector<int> const & newVec)
    {
      for ( auto const & vi : newVec )
       {
         if ( oldSet.cend() != oldSet.find(vi) )
            /* do something */ ;
       }
    }
 };

where the Matcher object is constructed with a vector that is used to initialize a std::set (or a std::multi_set , or a unordered set/multiset?) to make simple the work in matchOpticalFlowNaive()