Computer Science II — CSci 1200
Lecture 21
Priority Queues and Heaps
Review from Lecture 20
•Collision resolution
•Using a hash table to implement a set.
–Function objects
–Overall design
–Iterators
–Fundamental operations: find, insert and erase.
•We will complete our discussion today:
–Erase
–Resize
–Iterators
–Limitations
Today’s Class
•Idea of a priority queue
•A priority queue as a heap — a complete binary tree
•Percolate up and percolate down operations
•A heap as a vector
•Making a heap
•Heap sort
Priority Queue — Fundamental Operations
•Priority queues are used in prioritizing operations. Examples include jobs on a shop
floor, packet routing in a network, scheduling in an operating system, or events in a
simulation.
•Among the data structures we have studied, their interface is most similar to a queue,
including the idea of a front or top and a tail or a back.
•Each item is stored in a priority queue using an associated “priority” and therefore,
the top item is the one with the lowest value of the priority score.
–The tail or back is never accessed through the interface to a priority queue.
•The main operations are insert or push, and pop (or delete_min).
