ncs 301 data structure using c · ncs 301 data structure using c 03-08-15 subject notes by hammad...

NCS 301 Data Structure Using C 03-08-15

Subject Notes by Hammad Lari 1

NCS 301

DATA STRUCTURE USING C

Hammad Mashkoor Lari

Assistant Professor

Allenhouse Institute of Technology

www.ncs301ds.wordpress.com

Unit-1 Part-4 Linked Lists

Introduction

List refers to linear collection of data items.

Example:-shopping list

Data processing involves storing and processing data organized

into lists. One such way of storing is using arrays.

Advantages of arrays:-

Easy to compute the address of an element in an array(physical

relationship of data in memory).

Disadvantages:-

1. Relatively expensive to insert and delete elements

2. Array usually occupies a block of memory space one cannot

simply double or triple the size of array when required(arrays

are called dense lists) 03-08-2015



Continued….

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Another way of storing a list is to have each element in list

contain a field called a link or pointer which contain the address

of next element in the list.

No adjacent space.

Easy to delete and insert elements

This is called linked lists

Linked lists

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A linked list or one way list is a linear collection of data elements called

nodes where linear order is given by means of pointers.

Each node is divided into 2 parts:-

1. First part contains information about element

2. Second part called link or nextpointer field contains address of next node.

Pointer of last node contains a special value called null pointer which is

invalid address(in practice 0 or negative number is used for null)

List also contains list pointer variable called start or name which contains

address of first node in list.

x

start Linked list with 3 nodes



Representation of Linked Lists in memory Let LIST be a linked list. LIST requires two linear arrays (INFO & LINK).

List also requires a variable name such as START and nextpointer sentinel

NULL. We choose null=0.

Example:-

Refer page 5.4 from Data structures by Seymour Lipschutz(schaum)

Declaration for linear linked list in memory

Struct node

{

Int a ;

Struct node *next;

};

Typedef struct node NODE;

NODE *start;03-08-2015

Types of linked list1. Singly linked list-linear(we cannot access the predecessor of node from

current node)

2. Doubly ll-multiple links, accessing both predecessor and successor

3. Circular ll-no beginning and no end(sorting the address of very first node inlink field of last node)

4. Circular doubly ll-successor and predecessor pointer in circular manner.

Operations on Linked list

1. Creation

2. Insertion

3. Searching

4. Deletion

5. Traversing

6. Searching

7. Display 03-08-2015



Singly Linked list In C a ll is created using structure ,pointers and dyanamic memory

allocation.

Struct node

{

Int num;

Struct node *ptr; //pointer to node

};

Typedef struct node NODE //type def making it adt

NODE *start; //pointer to node of ll

Start=(NODE*)malloc (sizeof(NODE));//dynamic memory allocation //when thisline is executed NODE is allocated and assigns HEAD as starting address ofNODE(head is the external pointer)

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num ptrstart

NODE

Singly Linked list

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num ptrstart

NODE

Now we can assign values

Start->number=30;

Start->ptr=‘\0’ //null pointer

Start->ptr=(NODE *) malloc(sizeof(NODE));

Start->ptr.num=100;

Start->ptr.ptr=‘\0’



Inserting nodes in Singly linked list To insert an element following things should be done

1. Allocating a node

2. Assigning the data

3. Adjusting the pointers

Three instances of inserting

1. At the beginning

2. At the end

3. At specified position

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Insertion at the beginning

10

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302010

50403020

40 50

start

start

100

Node A

Node A

Before Insertion

After Insertion

New Nodeptr



Algorithm-insertion at beginningInsert(start,item)

1. Initialize NODE *p

2. p=(NODE *)malloc(sizeof(NODE))

3. if(p==NULL)

print insertion was not possible and exit for program

4. else

1. If(start==null)

P->next=null;

2. Else

P->next=start;

3. Start=p;

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Insertion at the end

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start

start

100 x

Before Insertion

After Insertion

ptr



Algorithm-insertion at the end

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Insert(start,item)

1. Initialize node *p,item

2. P=(NODE *)malloc(sizeof(NODE))

3. If(p==NULL)

Print NODE was not created and exit for program.

4. else

1. P->info=item

2. P->next=’\0’

3. If(start==NULL)

Start=p

4. Else

Temp=start

Repeat until (temp->next==’\0’)

Temp=temp->next

Temp->next=p

Insertion at the middle or specific location

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start

start

Node A Node B

Node A Node B

Before Insertion

After Insertion



Algorithm-insertion at specific position

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1. Initialize NODE *p,temp,loc


3. If(p==NULL)

Print NODE is not created and exit from

program.

4. Else

1. p->info=item

2. if(start==NULL)

1. start=p

2. P->next=null

3. Else(initialize counter I and temp pointers)

1.temp=start

2.i=1

3.Repeat until i<loc

1.temp=temp->next

2.i++

4.p=temp->next

5.temp->next=p

Deleting first node

10

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3020

50403020

40 50

start

start

Before deletion

After deletion

ptr



Algorithm-Delete from beginningdelete(start)

1. Check for underflow?

1. If start=null then

2. print no nodes

3. Exit

2. Set ptr=start

3. Set start=start->next

4. Print element deleted ptr->info

5. Free(ptr)

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Deleting last node

10

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3020

50 x403020

40 x

start

start

Before deletion

After deletion

ptr

10

loc



Algorithm-deletion from enddelete(start)



2. print no nodes

3. Exit

2. If start->next=null then

1. Set ptr=start

2. Set start=null

3. Print element deleted is ptr->info

4. Free(ptr)

3. Set ptr=start

4. Repeat until ptr->next!=null

1. Set loc=ptr

2. Set ptr=ptr->next

5. Set loc->next=null

6. Free(ptr)03-08-2015

Deleting node from specific position

10

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4020

50 x403020

50 x

start

start

Before deletion

After deletion

10



Algorithm-deletion from specific positiondelete(start)



2. print no nodes

3. Exit

2. Initialize counter, I and pointers

1. Node *temp, node *ptr;

2. Set i=0

3. Set ptr=start

3. Repeat steps 4 to 9 until i<=loc

4. Set temp=ptr

5. Set ptr=ptr->next

6. Set i=i+1

7. Print element deleted is

8. Set temp->next=ptr->new

9. Free(ptr) 03-08-2015

Circular Linked lists

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A circular linked list is a type of singly linked list in which the link field of the

last node contains the address of first node of the list.

List contains list pointer variable called start and last which contains address

of first node and last node in list.

x

start Linked list with 3 nodeslast



Algorithm-insertion at beginning1. Initialize NODE *P


3. If(p==NULL)

1. Print insertion was not possible

4. Else

1. p->info=item

2. if(start==NULL)

1. Start=last=p

2. P->next=start

3. Else

1. p->next=start

2. start=p

3. last->next=p

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Algorithm-insertion at end1. Initialize NODE *p

2. p=(NODE*)malloc(sizeof(NODE))

3. If(p==NULL)

1. Print insertion was not possible.

4. Else

1. P->info=item

2. If(start==NULL)

1.start=last=p

2.p->next=start

3. Else

1.Last->next=p

2.Last=p

3.Last->next=start03-08-2015



Algorithm-deletion from beginning1. Initialize NODE *p

2. if(start==NULL)

1. print 'UNDERFLOW'.

3. else

1. p=start

2. start=start->next

3. last->next=start

4. print p->info

5. free(p)

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Algorithm-deletion from end1. Initialize NODE *p,*temp.

2. if(start==NULL)

1. print 'UNDERFLOW'

3. else

1. p=start

2. repeat untill p->next !=start

1. temp=p

2. p=p->next

3. temp->next=start

4. last=temp

5. print p->info

6. free(p)

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Doubly Linked lists

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Disadvantage of Singly linked list:-

1. Inability to traverse the list in the backward direction.

A doubly linked list provides bi directional traversing.

Each node in D.L has two fields.

List contains list pointer variable called start and last which contains address

of first node and last node in list.

x x

start Doubly Linked list with 3 nodeslast

prev data next

Structure –Doubly linked list

struct node

{

struct node *prev;

struct node *next;

char info;

}

typedef struct node NODE

NODE *start;

NODE *last;

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Algorithm-insertion at beginning1. Initialize NODE *p


3. p->info=item

4. p->prev=NULL

5. if(start==NULL)

1. start=last=p

2. p->next=NULL

6. else

1. p->next=start

2. start->prev=p

3. start=p

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Algorithm-insertion at end1. Initialize NODE *p.


3. p->info= item

4. p->next=NULL

5. if(start==NULL)

1. start=last=p

2. p->prev=NULL

6. else

1. last->next=p

2. p->prev=last

3. last=p

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Algorithm-deletion from beginning1. Initialize *p.

2. if(start==NULL)

1. print ''UNDERFLOW''

3. else

1. p=start

2. start=start->next

3. start->prev=NULL

4. print p->info

5. free(p)

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Algorithm-deletion from end1. Initialize *p.

2. if(start==NULL)

1. print "UNDERFLOW"

3. else

1. If(last->prev==null)

1. P=last

2. Last->last->prev

3. Last->next=null

2. print p->info

3. free(p)

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Class Website

www.ncs301ds.wordpress.com

03-08-2015

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