C-Programming-Class 12

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Session 12

Linked List


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Session Objectives

To study the concepts of linked list.

To study the different operations performed

on the linked list.


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Session Topics

Introduction to linked list.

Singly linked list.

Circular linked list.


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Linked Lists

A linked listis a data structure which is a

collection of zero or more nodes where each

nodehas some information. Between, each node

in the list, there exists a logical relationship so

that given the address of the first node, any node

in that list can be obtained. Each node can hold

the data along with a pointer field using whichaddress of the next node can be obtained.


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Types of Linked Lists:

Singly linked lists

Circularly singly linked listsDoubly linked lists

Circular doubly linked lists


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Storage representation of a node

In a linked allocation technique, a node in a linked list has

two fields.

infowhich contains the actual information

linkwhich contains address of the next node

A node can be represented as astructure as follows

struct node

{

int info;struct node *link;

};


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Singly linked list

A singly linked list is a linked list, where each node has designated field

called link field which contains address of the next node. If there exists

only one link field in each and every node In the list, then the list is a

Singly Linked List.

10205

info link

nodefirst = 1004

101215

info link

1020

25

info link

1012

Memory representation of singly linked list

5 15 25

info link info infolink link first

node

10041020 1012

Pictorial Representation of Singly linked list


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Operations performed on singly linked list

Inserting a node into the list Deleting a node from the list

Display the contents of the list

temp20 30 40

10

first

To insert an item at the front end

10 20 30 40

firstAfter inserting 10


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Function to insert an item at the front end of

the list

NODE insert_front(int item,NODE first)

{

NODE temp;temp = get_node(); /* Obtain a node */

temp->info = item; /* Insert the item */

temp->link = first;

return temp; /* Return the first node */}


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Function to obtain a new node from the

availability list

NODE get_node(){

NODE x;

/* Try to allocate the required size of memory */

x = (NODE)malloc(sizeof(struct node));if(x == NULL)

{

printf(Out of memory\n);/*Allocation failed*/

exit(0);

}

/* Allocation successful, return address */

return x;

}


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To delete a node from the front end

10 20 30 40temp

first

first

10 20 30 40

temp

20 30 40first


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Function to delete an item from the front end

of the list

NODE delete_front(NODE first){

NODE temp;

if(first == NULL) /* Is list empty */

{

printf(List empty\n);return first;

}

/* Retain the address of the node to be deleted*/

temp = first;

first = first->link; /* Update first */

/* Display and delete the front node */

printf(The item deleted is %d\n,temp->info);

free_node(temp);

return first; /* return address of first node */

}


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To insert an item at the rear end

2010 30

first

cur

2010 30 40

tempfirst cur

2010 30 40


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Function to insert an item at the rear end of

the listNODE insert_rear(int item, NODE first)

{NODE temp; /* Node to be inserted */

NODE cur; /* To hold the address of the last node*/

temp = get_node();

temp ->info = item;

temp->link = NULL;

/* Return the new node created if list is empty*/if(first==NULL) return temp;

/* If list exists,obtain address of last node */

cur = first;

while(cur->link != NULL)

{

cur = cur->link;}

/* Insert the node at the end */

cur->link = temp;

/* Return address of the first node */

return first;

}


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Delete a node from the rear end

10first After deleting

first = NULL

10 20 30 40first

prev cur

prev

10 20 30 40first


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Function to delete an item from the rear end

of the list

NODE delete_rear(NODE first){NODE cur,prev;if(first == NULL){

printf(List empty!Cannot delete\n);return first;

}if(first ->link == NULL) { /* Only one node is

present and delete it*/printf(The item to be deleted is %d\n,first->info);

freenode(first); /*Return to availability list */first = NULL;return first;

}


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contd.Function to delete an item from the

rear end of the list

/* Obtain address of the last node and just previous to that */

prev = NULL;

cur = first;

while(cur->link!=NULL){

prev = cur;

cur = cur->link;

}

printf(The item deleted is %d\n,cur->info);

freenode(cur); /* Delete the last node */

prev->link = NULL; /* Node pointed to byprevis madethe last node*/

return first; /* Return address of the first node */

}


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Circular singly linked list

Linear linked list containing the address of the first node in the linkfield of the last node results in a Circular Singly linked listor

Circular list. last

Pictorial representation of Circular singly linked list

NOTE:

In a circular list if the address of any node x is known, one can traverse theentire list from that node and thus, all nodes are reachable.

Operations performed on a Circular list:

insert _front , insert_rear, delete_front, delete_rear


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To insert a node at the front end of a Circular

list

20 30 40

last

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10

last


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Function to insert an item at the front end of

the Circular listNODE insert_front(int item, NODE last)

{

NODE temp;

temp=get_node();/*Create a new node to be inserted*/temp->info = item;

if(last == NULL)/* Make tempas the first node */

last = temp;

else /*Insert at the front end */

temp->link = last->link;

last->link = temp; /*Link last node to first node*/

return last; /* Return the last node */

}


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Insert a node at the rear end

10 20 30

last

10 20 30 40

last temp


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Function to insert an item at the rear end of

the list

NODE insert_rear(int item,NODE last)

{

NODE temp;

temp = get_node; /*Create a new node */temp->info = item;

if(last == NULL)/*Make temp as the first node*/

last = temp;

else /*Insert at the rear end*/

temp->link = last->link;last->link = temp; /*Link last node to first node*/

return temp;/*Make the new node as the last node */

}


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Delete a node from the front end

10 20 30 40first last

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To delete an item from the front end

After deleting the first item


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Function to delete an item from the front end

of the list

NODE delete_front(NODE last){NODE temp,first;if(last == NULL) /* If no list exists */{

printf(List is empty\n);return NULL;

}

if(last->link ==last) /* Is there only one node? */{

printf(The item deleted is %d\n,last->info);free_node(last);return NULL;

}first=last->link; /*Obtain the item to be deleted*/

/*Store new first node in link of last*/last->link = first->link;printf(The item deleted is %d\n,first->info);free_node(first); /*Delete the old first node */return last;

}


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Function to delete a node from the rear end

10 20 30 40

10 20 30

To delete a node from the rear end

After deleting a node from the rear end


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Function to delete a node from the rear end

NODE delete_rear(NODE last){

NODE prev;

if(last == NULL) /* If no list exists */

{

printf(List is empty\n);

return NULL;

}

if(last->link ==last) /* Is there only one node? */{

printf(The item deleted is %d\n,last->info);

free_node(last);

return NULL;

}

prev = last->link; /*Obtain address of previous node*/

while(prev->link != last)prev = prev->link;

prev->link = last->link;/*prev node is made the last node*/

printf(The item deleted is %d\n,last->info);

free_node(last);/*Delete the old node*/

return prev; /* return the new last node */

}


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Summary

A singly linked list is a linked list, where each node hasdesignated field called link field which contains address ofthe next node.

If there exists only one link field in each and every node Inthe list, then the list is aSingly Linked List.

Linear linked list containing the address of the first node inthe link field of the last node results in a Circular Singlylinked listorCircular list.

In a circular list if the address of any node x is known, onecan traverse the entire list from that node and thus, allnodes are reachable.


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Thank You!

C-Programming-Class 12

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