901230 lecture5&6

FIST, Multi Media University

Lecture 5

• Stack (Array Implementation)

• Queue (Array Implementation )


Stack

What is a Stack?

1) It is a data structure for storing some values

2) It is an ADT.

3) Implemented using Arrays or Linked List

4) used in Operating System and in System Programming


Stack

How to Store and Retrieve from a Stack?

1) All Insertions ( Storing) and Deletions (Removing) of entries are made at one end called the TOP of Stack

2) Last item added to a stack (PUSH) is always the first that will be removed (POP) from the stack.

3) This property is called Last In First Out also known as LIFO

4) The operations are done with a single pointer to the top of list of elements.

Operations...


Stack

A

B

C

D

E TOPF

GEG - Plates

Books

(LIFO)


Operations

• There are Four operations :1) Push ( )

used to add the data at the top of the stack.

Check whether the stack is full or not

2) Pop ( )

used to remove data at the top of the stack.

Check whether the stack is empty or not

3) Empty ( )

Checks whether stack is empty, TOP = -1

4) Full ( )

checks whether stack is full, TOP = maxstacksize


Stack - implementation

• Uses ARRAY to represent a stack

Class stack

{ private :

int stackelement[10],TOP;

public:

stack( ) { top = -1}

void push(int);

int Pop( );

int Empty( );int Full ( );};


Stack

How to Push?Void stack :: Push(int data2add)

{ if (!Full( ))

{ TOP++;

Stackelement[TOP] = data2add;

}

else

cout << “Stack is Full!!!”<<endl;

}


Stack

How to Pop?Int stack :: Pop( )

{int data2remove;

if (!Empty( ))

{ data2remove = Stackelement[TOP];

TOP--; return data2remove; }

else{ cout << “Stack is Empty!!!”<<endl;

return 0;

} }


Stack

How to check for full?

Int Stack :: Full( )

{

if (TOP==9) return 1;

else return 0;

}


Stack

How to check for Empty?

Int Stack :: Empty( )

{

if (TOP== -1) return 1;

else return 0;

}


Stack

Void main( )

{

stack stackobj;

stackobj.Push(23);

stackobj.Push(46);

stackobj.Push(37);

stackobj.Push(10);

stackobj.Push(55);cout << stackobj.Pop( );cout << stackobj.Pop( );}

23

3746

1055

55

10


Applications of Stack

We shall see two applications of the stack

1) Use of Stacks in Function Calls

2) Palindrome Checking


Use of Stacks in Function Calls

• Whenever a function begins execution an ACTIVATION RECORD (Stack Frame) is created

• to store the current environment for that function which includes

Parameters

Caller’s state information

Local variables

Temporary storage

This structure should LIFO because , when a function terminates, the function with which to resume execution is the last function whose activation record was saved.


Stack

Function1

Function2

Function3

Function4

Activation Record

Function1

Function2

Function3


Palindrome Checking

What is a palindrome?

A palindrome is a word/sentence that is the same if read both ways.

You might have noticed that if you push some characters into a stack and pop them out , they will appear in reverse order.

So Stacks are used for this purpose.


Palindrome

Here are some palindromes

MALAYALAM (a south Indian language)

RATS LIVE ON NO EVIL STAR

DAD

POP

RADAR

STEP ON NO PETS

MADAM


implementation#include <iostream.h>

#include <string.h>

class ADTstack

{ char stack[10];

int topstack;

public: ADTstack( ) {topstack = -1;};

int empty() {if (topstack == -1) return 1; else return 0;};

int full() {if (topstack == 9) return 1; else return 0;};

void push(char num) { if (!full()) { topstack++;

stack[topstack] = num;

}

else cout<<" Stack is Full"<<endl;

}


implementation

char pop( )

{ char num;

if (!empty())

{

num = stack[topstack];

topstack--; return num;

}

else {cout<<"Stack is Empty"<<endl;

return '0';}

}

};


implementation

void main()

{

ADTstack st;

char str[10];

int palin, l,i;

cout<<"type in a string to check if it is a palindrome"<<endl;

cin>>str;

l=strlen(str);

if (l==1) {palin=1;} //all strings with 1 character are palindromes

else

{


implementation

i=0;

while(str[i]!='\0') //push the string into stack

{ st.push(str[i]);

i++;

}

i=0;

while(str[i]!='\0') //pop the string and compare with original

{ if (str[i]!=st.pop()) {palin=0;break;}

i++;

}

} if (palin==0) cout<<"Not Palindrome"<<endl;

else cout<<"Palindrome"<<endl;

}


Queue

What is a Queue?

1) It is a data structure for storing some values

2) It is an ADT.

3) Implemented using Arrays or Linked List


How to Store and Retrieve from a Queue?

1) A Data Structure in which all Additions to the list are made at one end, and all Deletions from the list are made at other end.

2) First item added to a queue (ADD) is always the first that will be removed (REMOVE) from the queue.

3) This property is called First In First Out also known as FIFO

4) It can be maintained with two pointers namely FRONT (REMOVE) and REAR ( ADD).

Queue


Queue

Front Rear

EG - Bank Counter


Operations

There are Four operations :

1) Addend ( )

used to add the data at the Tail of the Queue.

Check whether the Queue is full or not

2) Serve ( )

used to remove data at the top of the stack.

Check whether the Queue is empty or not

3) Empty ( )

Checks whether Queue is empty, Tail = -1

4) Full ( )

checks whether Queue is full, Tail = maxqueuesize


implementation

Uses ARRAY to represent a Queue

Class Queue

{ private :

int Queueelement[4],Head ,Tail;

public:

Queue( ) { Head =0 ; Tail = -1}

void Addend(int);

int Serve( );

int Empty( );int Full ( );};


implementation

How to check for full?

Int Queue :: Full( )

{

if (Tail == 3) return 1;

else return 0;

}


implementation

How to check for Empty?

Int Queue :: Empty( )

{

if (Tail == -1) return 1;

else return 0;

}


implementation

How to Add?

Void Queue :: Addend(int data2add)

{ if (!Full( ))

{ Tail++;

Queueelement[Tail] = data2add;

}

else

cout << “Queue is Full!!!”<<endl;

}


implementation

How to Delete?

int Queue :: Serve( )

{int data2remove;

if (!Empty( ))

{ data2remove = Queueelement[0];

for ( i =0;i<Tail;i++)

Queueelement[i] = Queueelement[i+1]

Tail--; return data2remove; }

else{ cout << “Queue is Empty!!!”<<endl;

return 0; } } Methods


implementation

Void main( )

{

Queue queueobj;

queueobj.Addend(23);





cout << queueobj.Serve();cout << queueobj.Serve();}

23 46 37 10 55

23 46


Serving

Three Methods of Serving1) increment head to 1

runs out of storage

2) when the first person has be served the remaining persons in the Queue shuffle forward one place.

Can serve unlimited number of persons as long as the queue never exceeds the maximum size

3) Use cyclic queues

One of the application of Queues is simulation


Lecture 6

• Cyclic Queues


Cyclic Queues

What is a Cyclic Queue?

we need to imagine that the array allocated to the queue

is not linear but cyclic, i.e. that it forms a circle.

EG:

So that if for instance 10 elements are allocated to the queue with the element positions running from 0 to 9 then when the tail gets to position 9 the next element to be added can go to position 0 providing that position has already been “served” (vacant).

.Thus the two problems of the queues are solved .


Cyclic Queue

Head Tail

0 1 2 3 4 5

The following actions will cause the “head” and “tail” tomove through the array as listed below:

Example: Queue implemented using an array of size 6 with 4 data items inserted in to the queue


Cyclic Queue

Action Head Tail

0 3

Delete 1 3

Insert 1 4

Delete 2 4

Insert 2 5

Insert 2 0

Delete 3 0

Delete 4 0

Head Tail

0 1 2 3 4 5


Cyclic Queue

Action Head Tail

Insert 4 1

Delete 5 1

Insert 5 2

Delete 0 2

Note: A Cyclic queue will always be of fixed size (say n) and the size information must be available to update the pointers “head” and “tail”.

Head Tail

0 1 2 3 4 5


Cyclic Queue

The wrapping around can be achieved by updating the pointers as follows:

Delete: head = (head+1) % n

Insert: tail = (tail + 1) % n

i.e., Whenever a pointer is incremented, take modulo n.

The above operations is needed to check if the queue is empty or full.


Cyclic Queue

Consider when there is only one element in the queue• In this case, both the pointers coincide (head == tail)• The queue becomes empty when the element is deleted

Tail HeadHead ,Tail

0 1 2 3 4 5 0 1 2 3 4 5

Only one element Queue Empty Queue


Cyclic Queue

For an empty queue, we have the condition

head = (tail + 1) % n

The above condition is also satisfied when the queue is full

We resolve the ambiguity between two cases

if the condition head = (tail+1)% n is satisfied up on deleting an item from the queue, then queue is empty

if the condition head = (tail + 1) % n is satisfied up on inserting an item in to the queue, then queue is full.


implementation

How to Add?void Addend(int x)

{

if (!Full())

{

tail=(tail+1)%MAX;

a[tail]=x;

count++;

cout<<x<<" added to the queue"<<endl;

}

else cout<<"Full Queue"<<endl;

}


implementation

How to Delete?int Serve()

{ int x;

if (!Empty())

{

x=a[head];

head=(head+1)%MAX;

count--;

cout<<x<<" served from the queue"<<endl;

return x;

}

else cout<<"Empty Queue"<<endl; }

901230 lecture5&6

Education

Transcript of 901230 lecture5&6