lecture - stack adt.pdf

7/28/2019 Lecture - Stack ADT.pdf

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Data Structures CSC212 (1)

Stack ADTStack ADT

Dr Muhammad Hussain Lecture - Stack ADT


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Stack ADTStack ADTAn ADT that manages data elements linearly but provides access at only oneend i.e. data elements can be inserted and removed from one end only.

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NOTE:NOTE:

InIn Stack ADT, the elements are removed only in the inverse orderStack ADT, the elements are removed only in the inverse order


o t e r arr va .e. t e ast nserte e ement s remove rst o a .o t e r arr va .e. t e ast nserte e ement s remove rst o a .

So, it has lastSo, it has last--in/firstin/first--out (LIFO) behavior.out (LIFO) behavior.


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handled using stackhandled using stack The a ers ut in the tra of aThe a ers ut in the tra of a rinter. Therinter. The a ersa ers

from the tray are removed by the printer infrom the tray are removed by the printer in reversereverse

order they are put in theorder they are put in the tray.tray. StackStack is used to evaluate expressions likeis used to evaluate expressions like 1010x((1212++77))

AA runtime system uses a stack to handleruntime system uses a stack to handle functionfunction

..



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S ecification of Stack ADTS ecification of Stack ADTElementsElements:: Any valid data typeAny valid data typeStructureStructure:: AnAn arrangement of elements that allows to removearrangement of elements that allows to remove

DomainDomain:: Number of elements is boundedNumber of elements is boundedOperationsOperations ::OperationOperation SpecificationSpecification

booleanboolean empty()empty()Precondition/Requires:Precondition/Requires: nonenone

Processing/Results:Processing/Results: returns true if the stack is empty otherwise false.returns true if the stack is empty otherwise false.

booleanboolean full()full()

Precondition/Requires:Precondition/Requires: nonenone

Processing/Results:Processing/Results: returns true if no more elements can be insertedreturns true if no more elements can be inserted

into the stack otherwise false.into the stack otherwise false.

void push(Type)void push(Type)

Processing/Results:Processing/Results: inserts a given element into the stack at the topinserts a given element into the stack at the top

and top points to it.and top points to it.

Precondition/Requires:Precondition/Requires: stack is not emptystack is not empty


Type pop()Type pop() Processing/Results:Processing/Results: the element at the top of the stack is removedthe element at the top of the stack is removed

from the stack and returned.from the stack and returned.


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Re resentation of Stack ADTRe resentation of Stack ADTStack ADT can be represented asStack ADT can be represented as

-- ArrayArray

-- Linked ListLinked List

0

1

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Null


n -

Array


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public classArrayStackArrayStack

//Data Membersprivate int maxsize;

pr va e n op;

private T[] nodes;

// Operationspublic ArrayStack(int n)

Public boolean empty()

public void push(T e)

public T pop()



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publicArrayStack(int n)

maxsize =n;top = -1;nodes = (T[]) new Object[n];

}

public boolean empty()

return top == -1;}



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public boolean full()

{return top == maxsize - 1;


if(full()) return;top++;

no es op = e;}



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public T pop(){

return nodes[top--];}



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Linked List based Implementation of Stack ADTLinked List based Implementation of Stack ADT

public class LinkStackLinkStack

// Data Memebrsprivate Node top;

// Operations

public LinkStack()

public boolean full()


pu c pop}



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Node tmp = new Node(e);tmp.next = top;

}

{

Node tmp = top;

T e = top.data;top = top.next;


}


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Array Based Implementation

- An arra based im lementation suffers from the drawback that

all the storage space must be reserved in advance and themaximum depth of the stack is limited to this arrays size.

- .

Linked List based Implementation

- The time complexity of all operations is O(1). For applications in which the maximum stack size is known

ahead of time, an array is suitable

,

a linked list



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A lication of Stack ADTA lication of Stack ADTInfix Expressions- An expression in which everybinary operation appears between

Example: (i) a+b + is a binary operation and a andb areits operands

*

Prefix Expressions

- An expression in which operator comes before its operands

(ii) (a+b)*c *+abc

(iii) a+(b*c) +a*bc

- An expression in which operator comes after its operands

Example: (i) a+b ab+


a c a c

(iii) a+(b*c)

abc*+


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Application of Stack ADT Some calculators require that the input expression be in postfixform

them to postfix form

Problem: Convert the infix expression a - (b+c)*d into postfix

Method: Peroform the following steps with a stacks wr te a a

push(s, -)

push(s, ( )

write b abpush(s, +)


When right parenthesis ( is found, pop(s, +) and write it abc+


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pop(s, ( )

push(s, *)

write d

abc+dpop(s, *) write it abc+d*

- * -

Exercise

,

r e a unc on a conver s an n x express on o s

postfix form using a stacks and its operations given in the

specification of stack ADT.


lecture - stack adt.pdf

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