CSCI 240 Abstract Data Types

1
Department of Computer and Information
Science,School of Science, IUPUI
CSCI 240
Abstract Data Types
Queues
Dale Roberts, Lecturer IUPUI droberts_at_cs.iupui.edu
2
Queues

• Queue
• Similar to a supermarket checkout line
• First-in, first-out (FIFO)
• Nodes are removed only from the head
• Nodes are inserted only at the tail
• Insert and remove operations
• Enqueue (insert) and dequeue (remove)
• Queue Model
• queue is a list, with insertion done only at one
  end and deletion done at the other end.
• Linked list implementation of queues
• operating as a list
• constant time for enqueue dequeue (keeping
  pointer to both the head and tail of the list)

3
DYNAMICALLY LINKED STACKS AND QUEUES
Figure 4.10 Linked Stack and queue (p.147)
4
FIFO queue ADT interface

• template ltclass Itemgt
• class QUEUE
• private
• // Implementation-dependent code
• public
• QUEUE(int)
• int empty()
• void put(Item)
• Item get()

5
FIFO queue linked-list implementation

• template ltclass Itemgt
• class QUEUE
• private
• struct node
• Item item node next
• node(Item x)
• item x next 0
• typedef node link
• link head, tail
• public
• QUEUE(int)
• head 0
• int empty() const
• return head 0
• void put(Item x)
• link t tail
• tail new node(x)

6
FIFO queue array implementation
We can implement get and put operations for the
FIFO queue ADT in constant time, using either
arrays or linked-lists.

• template ltclass Itemgt
• class QUEUE
• private
• Item q int N, head, tail
• public
• QUEUE(int maxN)
• q new ItemmaxN1
• N maxN1 head N tail 0
• int empty() const
• return head N tail
• void put(Item item)
• qtail item tail tail N
• Item get()
• head head N return qhead

If head tail, then empty if put would make
them equal, then full. Array is 1 larger to
allow checks.
7
First-class ADT
Our Fraction ADT is a first-class ADT.

• Sedgewick Definition 4.4
• A first-class data type is one for which we
  can have potentially many different instances,
  and which we can assign to variables which we
  declare to hold the instances.

8
First-class Queue ADT

• template ltclass Itemgt
• class QUEUE
• private
• // Implementation-dependent code
• public
• QUEUE(int)
• QUEUE(const QUEUE)
• QUEUE operator(const QUEUE)
• QUEUE()
• int empty() const
• void put(Item)
• Item get()

Notice how each and every interface operations
now includes a references to a particular Q. We
can create as many queues as we need.
9
Acknowledgements

• All of this code is from Horowitz, Sahni, and
  Anderson-Freed, Fundamentals of Data Structures
  in C.
• Some slides were originally developed by Chen,
  Hsin-His.