Queue Data Type (6.1)

















What's a Queue?


	1. a line of customers waiting for service
	2. a List with restricted access
	3. only the item at the front of the queue is accessible
	4. FIFO (First In First Out)
	5. items come out in the order they were added

















What operations are supported by a Queue?
What's the abstract interface for a Queue?


	add (item);
	remove ();
	front();
	empty();

















Classwork
You may work with a partner.

What does the program print?

	Queue Q1;
	Q1.add(4);
	Q1.add(2);
	Q1.add(4);
	Q1.add(8);
	print(Q1);

	Queue Q2;
	Queue Q3;
	while (!Q1.empty()) {
	    Q2.add(Q1.remove());
	    Q3.add(Q1.remove());
	}
	print(Q2);
	print(Q3);

	while (!Q2.empty())
	    Q3.add(Q2.remove());
	print(Q3);

















What kinds of applications is a Queue good for?
What kinds of problems can be solved using a Queue?


	1. request queue for a server (with fair service)
	2. simulation

















Queues in the C++ Library


	#include <queue>

	std::queue


What are some of the operations supported by std::queue?


	void push ( const ItemType& x );
	void pop ( );  // does not return the popped item
	ItemType& front ( );
	bool empty () const;
	size_t size() const;

















Priority Queue Data Type (8.5 pages 489-490)

















What's a Priority Queue?


	1. a Queue where the order of service is based on priority
	2. each item in the queue is assigned a priority
	3. only the highest-priority item is accessible

















What operations are supported by a Priority Queue?
What's the abstract interface for a Priority Queue?


	add (item);
	remove ();
	top();
	empty();

















Classwork
You may work with a partner.

What does the program print?

	PriorityQueue Q1;
	Q1.add(8);
	Q1.add(2);
	Q1.add(4);
	Q1.add(1);
	print(Q1);

	PriorityQueue Q2;
	PriorityQueue Q3;
	while (!Q1.empty()) {
	    Q2.add(Q1.remove());
	    Q3.add(Q1.remove());
	}
	print(Q2);
	print(Q3);

	while (!Q2.empty())
	    Q3.add(Q2.remove());
	print(Q3);

















What are some examples where Priority Queues are used?


	when smaller requests should be serviced first

















Priority Queues in the C++ Library


	#include <queue>

	std::priority_queue


What are some of the operations supported by std::priority_queue?


	void push ( const ItemType& x );
	void pop ( );  // does not return the popped item
	ItemType& top ( );
	bool empty () const;
	size_t size() const;