the most efficient and fastest way to compare elements in a vector?

Question

What is the most efficient and fastest way to compare elements in a vector of class using two iterators? The vector is not a sortable one and I have an overloaded ">" operator for the class. I use boost foreach for simple vector iterations.

I am doing something similar to the one given below.

vector<TestClass*> vec; 
vector<TestClass*>::iterator jIter;     
bool isErased=false;
vector<TestClass*>::iterator iIter = vec.begin();
if(!vec.empty()){
    while(iIter < vec.end()-1) {            
        isErased = false;
        for (jIter = iIter+1; jIter < vec.end();jIter++) {          
            if((*(*iIter))<=(*(*jIter))) {
                delete *jIter;
                jIter = vec.erase(jIter);               
                jIter--;
            }               
            else if((*(*iIter))>=(*(*jIter))) {                 
                delete *iIter;
                iIter = vec.erase(iIter);
                isErased = true;
                break;
            }               
        }
        if(!isErased) iIter++;
    }               

Thank you.

Answer 1

The most tricky part is to avoid running into invalidated iterators:

v.erase(std::remove_if(v.begin(), v.end(), [j](T const &i) { return i > j; });

You could also employ a loop, but use reverse iterators in that case

PS: I can't grok what you actually wanted achieve in your algorithm

You might be interested in

• is_sorted_until
• partition_point
• adjacent_find

Answer 2

Untested but something like this.

 for(auto it=vec.begin(), end=vec.end(); it!=end; ++it) {
   const auto&& val=*it;
   std::size_t count=0u;
   end=std::remove_if(
       it, end,
       [&](const TestClass& tc) -> bool {
           if(tc==val) ++count;
           return (count > 1);
       }
   );
 }
 vec.erase(end, vec.end());