std::priority_queue 与 std::set 之间的性能差异

Question

I am testing the performance difference between priority queue implementation of std::priority_queue vs implementation using std::set.

I have overloaded the < operator to sort based on score, in case when scores are equal use the next argument i. Also I am just calling the push,pop and top function to find the total time taken for these three operations.

In both implementation I am calling this 'timeQueue' function over 200 iterations and averaging the time obtained. I am seeing the std::set implementation takes around 38% faster. What could be the reason. Thank you.

(These are just for testing purpose)

std::set implementation

void timeQueue()

{
        NodeData res;
        for(int i=1;i<=500000;i++)
        {
                
                auto score = rand() %10000000;
                NodeData n1 = {i,i,score,i,i};
                // push:
                priorityList.insert(n1);
                
        }       
        for(int i=1;i<=500000;i++)
        {       
                std::set<NodeData>::iterator it = priorityList.begin(); 
                // top:
                auto s = it->id;
                // pop:
                priorityList.erase(it);
        }
}

Similarly, std::priority_queue

void timeQueue()
{
 NodeData res;
        for(int i=1;i<=500000;i++)
        {
                auto score = rand() % 10000;
                NodeData n1 = {i,1,score,1,1};
                priorityList.push(n1);
        }
        for(int i=1;i<=500000;i++)
        {
                res = priorityList.top();
                priorityList.pop();
                //std::cout<<res.id<<std::endl; 
        }
}
};

Answer 1

I think the reason for this performance difference is in set the elements are randomly generated and if by chance the generated elements are not unique, they are not inserted. Hence in effect, the std::set will have lesser elements than the std::priority_queue. And so lesser execution time.