How to remove element not at top from priority_queue?

In my program I need to delete an element from a priority queue that is not at the top. Can that be done? If not, please suggest a way to do so except creating your own heap.

The standard priority_queue<T> can be customized through inheritance. It has protected members c and comp that can be referenced in a descendant class.

template<typename T>
class custom_priority_queue : public std::priority_queue<T, std::vector<T>>
{
  public:

      bool remove(const T& value) {
        auto it = std::find(this->c.begin(), this->c.end(), value);
        if (it != this->c.end()) {
            this->c.erase(it);
            std::make_heap(this->c.begin(), this->c.end(), this->comp);
            return true;
       }
       else {
        return false;
       }
 }
};

void main()
{
   custom_priority_queue<int> queue;

   queue.push(10);
   queue.push(2);
   queue.push(4);
   queue.push(6);
   queue.push(3);

   queue.remove(6);

   while (!queue.empty())
   {
      std::cout << queue.top();
      queue.pop();

      if (!queue.empty())
      {
        std::cout << ", ";
      }
   }

 }

Output:

10, 4, 3, 2

The best solution is to use std::set. Sets provide methods which allow it to be used both as a min/max heap (or a priority queue).

std::set<int> pq;

//accessing the smallest element(use as min heap)
*pq.begin();

//accessing the largest element (use as max heap)
*pq.rbegin();

Furthermore sets also allow random deletion.

//to delete the integer '6'
auto it = pq.find(6);
pq.erase(it);

A neat little trick to handle deletes for a priority_queue STL - use another priority_queue, say, del_pq. Keep inserting all the delete values to this. When you are popping values from the original priority queue, check with top of del_pq and see if we wanted to delete it. If it matches, delete the value from the original priority_queue.

This method implements a way to lazily delete the values in our original priority queue. Can take up twice the memory, but average delete and inserts remain O(logN).