C++ Priority Queues

C++ Priority Queues are like queues, but the elements inside the queue are ordered by some predicate.

Constructors	construct a new priority queue
empty	true if the priority queue has no elements
pop	removes the top element of a priority queue
push	adds an element to the end of the priority queue
size	returns the number of items in the priority queue
top	returns the top element of the priority queue