chapter 3
DESCRIPTION
Chapter 3. Stacks. Chapter Objectives. To learn about the stack data type and how to use it To understand how Java implements a stack To learn how to implement a stack using an underlying array or linked list - PowerPoint PPT PresentationTRANSCRIPT
CHAPTER 3Stacks
Chapter Objectives To learn about the stack data type and how to use it To understand how Java implements a stack To learn how to implement a stack using an
underlying array or linked list To see how to use a stack to perform various
applications, including finding palindromes, testing for balanced (properly nested) parentheses, and evaluating arithmetic expressions
Section 3.1
Stack Abstract Data Type
The Stack ADT (§4.2) A stack is one of the most
commonly used data types. The Stack ADT stores
arbitrary objects Insertions and deletions
follow the last-in first-out scheme (LIFO)
Think of a spring-loaded pez dispenser
Main stack operations: push(object): inserts an
element object pop(): removes and
returns the last inserted element
Auxiliary stack operations: object peek(): returns
the last inserted element without removing it
integer size(): returns the number of elements stored
boolean empty(): indicates whether no elements are stored
Section 3.2
Stack Applications
Balanced Parentheses When analyzing arithmetic expressions,
it is important to determine whether an expression is balanced with respect to parentheses
( a + b * ( c / ( d – e ) ) ) + ( d / e )
The problem is further complicated if braces or brackets are used in conjunction with parentheses
The solution is to use stacks!
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Parentheses Matching Each “(”, “{”, or “[” must be paired with
a matching “)”, “}”, or “[” correct: ( )(( )){([( )])} correct: ((( )(( )){([( )])} incorrect: )(( )){([( )])} incorrect: ({[ ])} incorrect: (
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Figure 6.2Traces of the algorithm that checks for balanced braces
Section 3.3
Implementing a Stack
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Figure 6.4An array-based implementation
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Figure 6.5A reference-basedimplementation
Section 3.4
Additional Stack Applications
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Figure 6.7The action of a postfix calculator when evaluating the expression 2 * (3 + 4)
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Figure 6.8A trace of the algorithm that converts the infix expression a - (b + c * d)/e to postfix form