This document discusses algorithms for inserting nodes into singly linked lists at different positions. It provides pseudocode and illustrations for inserting a node after a given element, before a given element, and at a specified position. For each insertion operation, it outlines the steps: 1) create a new node, 2) get the data, 3) check for empty list or specified position and traverse the list to find the insertion point. It then shows how to insert the new node by adjusting the next pointers of the preceding and current nodes. Examples are given with initial and final list illustrations for each insertion type.

1. DATA STRUCTURES
Dr. P. Subathra
Professor
Dept. of Information Technology
KAMARAJ College of Engineering & Technology

2. CS8391 – DATA STRUCTURES
ONLINE CLASSES – CLASS NO. 3
18.08.2020
(04:00 PM – 05:00 PM)

3. UNIT 1
SINGLY LINKED LIST

4. INSERT
AFTER
AN ELEMENT

5. INSERT AFTER AN ELEMENT
Algorithm :
• STEP 1 : Dynamically generate a new node.
• STEP 2 : Get the value in the node’s data field.
• STEP 3 :
i. Check if the list is empty, if so display a message and
return.
ii. Traverse the list until the specified node is reached
or End of List is reached.
a. If element is found, insert the new element after the
current node
b. Else if end of list is reached, display a message of
ELEMENT NOT FOUND and return

6. • Initial List
• Insert 8 after 6
INSERT AFTER AN ELEMENT

7. • Initial List
• Insert 8 after 6
• Final List
INSERT AFTER AN ELEMENT

8. ALGORITHM
STEP 1 : Dynamically generate a
new node.
STEP 2 : Get the value in the
node’s data field.
CODE & ILLUSTRATION
INSERT AFTER AN ELEMENT

9. ALGORITHM
STEP 3:
i. Check if the list is empty,
if so, display a message and
return
CODE & ILLUSTRATION
INSERT AFTER AN ELEMENT
if (head==NULL)
{
prinft(“Empty List”);
return(); //optional
}
NULL
head

10. ALGORITHM
STEP 3 :
ii. Else traverse the list until the
specified node is reached or
End of List is reached.
a. If element is found, insert the
new element after the current node
b. Else if end of list is reached,
display a message of ELEMENT NOT
FOUND and return
CODE & ILLUSTRATION
INSERT AFTER AN ELEMENT
else
{
node * current = head;
while (current  data ! = searchElement
|| currentnext!=NULL)
{
current = current  next;
}
}

11. ALGORITHM & CODESTEP 3 :
ii. Else traverse the list until the specified node
is reached or End of List is reached.
a. If element is found, insert the
new element after the current node
b. Else if end of list is reached,
display a message of ELEMENT NOT
FOUND and return
ILLUSTRATION
INSERT AFTER AN ELEMENT
else
{
node * current = head; while (current  data ! = searchElement
|| currentnext!=NULL) { current = current  next; }
if ( current data == element)
{
tempnext=current->next;
currentnext=temp;
}
else
printf(“Element not found”);
}

12. • Initial List
• Insert 8 after 6
• Final List
INSERT AFTER AN ELEMENT

13. INSERT
BEFORE
AN ELEMENT

14. INSERT BEFORE AN ELEMENT
Algorithm :
• STEP 1 : Dynamically create a new node
• STEP 2 : Get the value in the data field of the new node.
• STEP 3:
i. Check if the list is empty, if so display a message and return.
ii. Check if the node is available as the first node
a. Perform Insert First operation
iii. Traverse the list until the specified node is reached or End of
List is reached. While traversing, keep track of the previous
node also.
a. If element is found, insert the new element after the previous node
b. Else if end of list is reached, display a message of ELEMENT NOT
FOUND and return

15. ALGORITHM
STEP 1 : Dynamically generate a
new node.
STEP 2 : Get the value in the
node’s data field.
CODE & ILLUSTRATION
INSERT BEFORE AN ELEMENT

16. ALGORITHM
STEP 3:
i. Check if the list is empty,
if so, display a message and
return
CODE & ILLUSTRATION
INSERT BEFORE AN ELEMENT
if (head==NULL)
{
prinft(“Empty List”);
return(); //
}
NULL
head

17. ALGORITHM & CODE
STEP 3:
ii. Else check if the node is
available as the first node
a. Perform Insert First operation
(eg) Insert after 7
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else if (head-> data==element)
{
temp->next=head;
head=temp;
}
NULL
NULL
NULL

18. ALGORITHM & CODE
STEP 3:
iii. Else Traverse the list until the specified node is
reached or End of List is reached. While
traversing, keep track of the previous node
also.
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
node * previous=head;
node * current = head-> next;
while (current->data! = element
|| current->next!=NULL)
{
current= current-> next;
previous = previous->next;
}
}

19. ALGORITHM & CODE
STEP 3: iii.
a. If element is found, insert the new
element after the previous node
b. Else if end of list is reached, display a
message of ELEMENT NOT FOUND
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
node * previous=head;
node * current = head-> next;
while (current->data! = element
|| current->next!=NULL)
{
current= current-> next;
previous = previous->next;
}
if(current->data==element)
{
temp->next=prev->next;
prev->next = temp;
}
else
printf(“Element not found”);
}

20. ALGORITHM & CODE
STEP 3: iii.
a. If element is found, insert the new
element after the previous node
b. Else if end of list is reached, display a
message of ELEMENT NOT FOUND
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
node * previous=head;
node * current = head-> next;
while (current->data! = element
|| current->next!=NULL)
{
current= current-> next;
previous = previous->next;
}
if(current->data==element)
{
temp->next=prev->next;
prev->next = temp;
}
else
printf(“Element not found”);
}

21. INSERT BEFORE AN ELEMENT

22. INSERT AT
A POSITION

23. INSERT AT A POSITION
Algorithm :
STEP 1 : Dynamically create a new node.
STEP 2 : Read the new value into the element field of the new node.
STEP 3:
Let k= POSITION
i. Check if the list is empty, if so display a message and return.
ii. Check if k==1 (First Position)
a. Perform Insert First operation
iii. Traverse the list until the specified (k -1)th node is reached or End
of List is reached
a. If (k -1) is available in the list, then, insert the new element after the (k -1)th
node
Copy the (k-1)th nodes next field value into the next field of the new node.
Make the (k-1)th node to point to this new node.
b. Else if end of list is reached, display a message of ELEMENT NOT FOUND and
return

24. ALGORITHM
STEP 1 : Dynamically generate a
new node.
STEP 2 : Get the value in the
node’s data field.
CODE & ILLUSTRATION
INSERT AT A POSITION

25. ALGORITHM
STEP 3:
i. Check if the list is empty,
if so, display a message and
return
CODE & ILLUSTRATION
if (head==NULL)
{
prinft(“Empty List”);
return(); //
}
NULL
head
INSERT AT A POSITION

26. ALGORITHM & CODE
STEP 3:
ii. Check if k==1 (First Position)
a. Perform Insert First operation
ILLUSTRATION
else if (k== 1)
{
temp->next=head;
head=temp;
}
NULL
NULL
NULL
INSERT AT A POSITION

27. ALGORITHM & CODE
STEP 3:
iii.
Traverse the list until the specified (k -1)th
node is reached or End of List is reached
(eg) Let Position = 3
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
count =1; k = position;
current = head;
while (count <=(k-1) ||
current->next!=NULL)
{
current= current-> next;
count++;
}
}

28. ALGORITHM & CODE
STEP 3:
iii.
Traverse the list until the specified (k -1)th
node is reached or End of List is reached
(eg) Let Position = 3
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
count =1; k = position;
current = head;
while (count <=(k-1) ||
current->next!=NULL)
{
current= current-> next;
count++;
}
temp->next = current-> next;
current-> next = temp
}

29. ALGORITHM & CODE
STEP 3:
iii.
Traverse the list until the specified (k -1)th
node is reached or End of List is reached
(eg) Let Position = 3
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
count =1; k = position;
current = head;
while (count <=(k-1) ||
current->next!=NULL)
{
current= current-> next;
count++;
}
}
NULL

30. ALGORITHM & CODE
STEP 3:
iii. Traverse the list until the specified (k -1)th
node is reached or End of List is reached
(eg) Let Position = 3
ILLUSTRATION
INSERT BEFORE AN ELEMENT
else
{
count =1; k = position;
current = head;
while (count <=(k-1) ||
current->next!=NULL)
{
current= current-> next;
count++;
}
temp->next = current-> next;
current-> next = temp
}
NULL
NULL
NULL
NULL
NULL

31. END
OF
INSERTION
OPERATIONS