STL iterable container like priority_queue

Question

I'm new to STL containers (and C++ in general) so thought I would reach out to the community for help. I basically want to have a priority_queue that supports constant iteration. Now, it seems that std::priority_queue doesn't support iteration, so I'm going to have to use something else, but I'm not sure exactly what.

Requirements:

• Maintains order on insertion (like a priority queue)
• Pop from top of list
• Get const access to each element of the list (don't care about the order in the queue for this stage)

One option would be to keep a priority_queue and separately have an unordered_set of references, but I'd rather not have two containers floating around. I could also use a deque and search through for the right insertion position, but I'd rather have the container manage the sorting for me if possible (and constant-time insertion would be nicer than linear-time). Any suggestions?

Answer 1

There are two options that come to mind:

1) Implement your own iterable priority queue, using std::vector and the heap operation algorithms (see Heap Operations here ).

2) derive (privately) from priority_queue . This gives you access to the underlying container via data member c . You can then expose iteration, random access, and other methods of interest in your public interface.

Answer 2

Using a std::vector might be enough as others already pointed, but if you want already-ready implementation, maybe use Boost.Heap (which is a library with several priority queue containers): http://www.boost.org/doc/libs/1_53_0/doc/html/heap.html

Boost is a collection of libraries that basically complete the standard library (which is not really big). A lot of C++ developers have boost ready on their dev computer to use it when needed. Just be careful in your choices of libraries.

Answer 3

You can use (ordered) set as a queue. set.begin() will be your top element, and you can pop it via erase(set.begin()).

Answer 4

Have you observed heap ( std::make_heap ) ? It hasn't order inside of queue, but has priority "pop from top of list" which you need.