Linear Data Representation Queues and Stacks

1
Linear Data Representation- Queues and Stacks

• There are collections of components arranged in a
  straight line.
• With restrictions on where to add and delete from
  the structure, we have two special structures
  Stack and Queue
• Both these ADT obey certain growth and decay
  laws
• Both can be represented by
• Linked list
• Sequentially
• Stacks are useful in processing nested data
  structures ( I.e algorithms in which programs
  call on subprograms like in sub-expressions

2

• That is whenever a method calls on another
  method/or itself (recursive) stacks are natural.
• Also algorithms that do parsing, evaluations and
  backtracking.
• QUEUES
• Can be used for regulating the processing of
  tasks in a system for fairness waiting queue
• When regulating processes then algorithms like
  FIFO can be used
• Queuing discipline can also be used in
  simulations and modeling

3

• STACKS
• Have two basic operations push and pop
• Stacks are sometimes called LIFO
• Is a sequence of items together with the
  following operations
• Construct an empty stack
• Determine whether a stack S is empty
• Push an item on the stack S
• Pop an item off S
• Peek at the top item on S.
• See figure 6.3

4

• QUEUE is a sequence of items with the following
  operations
• Construct and empty queue
• Determine whether queue Q is empty
• Insert in Q
• Remove from Q
• See fig 6.4
• These operations can be carried out using both
  linked list and sequential representation of both
  ADTs ( stack and queue)
• Example1 for the expression Ya2 (bc)2
  (de)2
• This consist of parenthesis, brackets, and
  braces.

5

• Example 2 Using ADT to evaluate Postfix
  expressions
• Consider e x y- z
• This is written as xy-z-
• Implementation of a stack
• Using sequential representation see program
  6.11
• Using linked list representation see program
  6.12
• Also see the use of stacks recursive calls -see
  programs 6.13 and figures 6.14 6.18.

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• Implementation of the Queue ADT
• Using sequential representation
• Use modular arithmetic to keep values in the
  range I.e xn ( 0, n-1
• This causes the increasing rear of the queue to
  wrap around so front (front 1) n and rear
  (rear 1)n always wrap around.
• See program 6.22
• Using a linked list representation see program
  6.23
• We should use linked lists when the size of the
  list is not known before hand and use an array
  otherwise.