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Double
Linked List
What is Double Linked List?
In a single linked list, every node has link to its
next node in the sequence. So, we can traverse from one node to other node only
in one direction and we can not traverse back. We can solve this kind of problem
by using double linked list. Double linked list can be defined as follows...
Double linked list is a
sequence of elements in which every element has links to its previous element
and next element in the sequence.
In double linked list, every node has link to its
previous node and next node. So, we can traverse forward by using next field
and can traverse backward by using previous field. Every node in a double
linked list contains three fields and they are shown in the following figure...
Here, 'link1' field is used to store the address of
the previous node in the sequence, 'link2' field is used to store the address of
the next node in the sequence and 'data' field is used to store the actual
value of that node.
Example
☀
In double linked list, the first node must be always pointed by head.
☀ Always the previous field of the first node must be NULL.
☀ Always the next field of the last node must be NULL.
☀ Always the previous field of the first node must be NULL.
☀ Always the next field of the last node must be NULL.
Operations
In a double linked list, we perform the following
operations...
1. Insertion
2. Deletion
3. Display
Insertion
In a double linked list, the insertion operation
can be performed in three ways as follows...
1. Inserting At Beginning of
the list
2. Inserting At End of the
list
3. Inserting At Specific
location in the list
Inserting At
Beginning of the list
We can use the following steps to insert a new node
at beginning of the double linked list...
- Step
1: Create a newNode with
given value and newNode → previous as NULL.
- Step
2: Check whether list is Empty (head == NULL)
- Step
3: If it is Empty then,
assign NULL to newNode → next and newNode to head.
- Step
4: If it is not Empty then, assign head to newNode → next and newNode to head.
Inserting At End
of the list
We can use the following steps to insert a new node
at end of the double linked list...
- Step
1: Create a newNode with
given value and newNode → next as NULL.
- Step
2: Check whether list is Empty (head == NULL)
- Step
3: If it is Empty, then assign NULL to newNode → previous and newNode to head.
- Step
4: If it is not Empty, then, define a node pointer temp and
initialize with head.
- Step
5: Keep moving the temp to
its next node until it reaches to the last node in the list (until temp → next is equal to NULL).
- Step
6: Assign newNode to temp → next and temp to newNode → previous.
Inserting At
Specific location in the list (After a Node)
We can use the following steps to insert a new node
after a node in the double linked list...
- Step
1: Create a newNode with
given value.
- Step
2: Check whether list is Empty (head == NULL)
- Step
3: If it is Empty then,
assign NULL to newNode → previous & newNode → next and newNode to head.
- Step
4: If it is not Empty then, define two node pointers temp1 & temp2 and
initialize temp1 with head.
- Step
5: Keep moving the temp1 to
its next node until it reaches to the node after which we want to insert
the newNode (until temp1 → data is equal to location, here location is the node value
after which we want to insert the newNode).
- Step
6: Every time check
whether temp1 is reached to the last node. If
it is reached to the last node then display 'Given node is not found in the list!!! Insertion not
possible!!!' and
terminate the function. Otherwise move the temp1 to
next node.
- Step
7: Assign temp1 → next to temp2, newNode to temp1 → next, temp1 to newNode → previous, temp2 to newNode → next and newNode to temp2 → previous.
Deletion
In a double linked list, the deletion operation can
be performed in three ways as follows...
1. Deleting from Beginning of
the list
2. Deleting from End of the
list
3. Deleting a Specific Node
Deleting from
Beginning of the list
We can use the following steps to delete a node
from beginning of the double linked list...
- Step
1: Check whether list is Empty (head == NULL)
- Step
2: If it is Empty then,
display 'List is Empty!!! Deletion is not
possible' and
terminate the function.
- Step
3: If it is not Empty
then, define a Node pointer 'temp' and initialize with head.
- Step
4: Check whether list is
having only one node (temp
→ previous is equal to temp → next)
- Step
5: If it is TRUE, then set head to NULL and
delete temp (Setting Empty list
conditions)
- Step
6: If it is FALSE, then assign temp → next to head, NULL to head → previous and delete temp.
Deleting from End
of the list
We can use the following steps to delete a node
from end of the double linked list...
- Step
1: Check whether list is Empty (head == NULL)
- Step
2: If it is Empty, then display 'List is Empty!!! Deletion is not possible' and terminate the function.
- Step
3: If it is not Empty
then, define a Node pointer 'temp' and initialize with head.
- Step
4: Check whether list has
only one Node (temp → previous and temp → next both are NULL)
- Step
5: If it is TRUE, then assign NULL to head and
delete temp. And terminate
from the function. (Setting Empty list condition)
- Step
6: If it is FALSE, then keep moving temp until
it reaches to the last node in the list. (until temp → next is equal to NULL)
- Step
7: Assign NULL to temp → previous →
next and delete temp.
Deleting a
Specific Node from the list
We can use the following steps to delete a specific
node from the double linked list...
- Step
1: Check whether list is Empty (head == NULL)
- Step
2: If it is Empty then,
display 'List is Empty!!! Deletion is not
possible' and
terminate the function.
- Step
3: If it is not Empty,
then define a Node pointer 'temp' and initialize with head.
- Step
4: Keep moving the temp until
it reaches to the exact node to be deleted or to the last node.
- Step
5: If it is reached to
the last node, then display 'Given node not found in the list!
Deletion not possible!!!' and terminate the fuction.
- Step
6: If it is reached to
the exact node which we want to delete, then check whether list is having
only one node or not
- Step
7: If list has only one
node and that is the node which is to be deleted then set head to NULL and
delete temp (free(temp)).
- Step
8: If list contains
multiple nodes, then check whether temp is the first node in the list (temp == head).
- Step
9: If temp is
the first node, then move the head to the next node (head = head → next), set head of previous to NULL (head → previous = NULL) and delete temp.
- Step
10: If temp is
not the first node, then check whether it is the last node in the list (temp → next == NULL).
- Step
11: If temp is
the last node then set temp of previous of next to NULL (temp → previous →
next = NULL)
and delete temp (free(temp)).
- Step
12: If temp is
not the first node and not the last node, then set temp of previous of next to temp of next (temp → previous →
next = temp → next), temp of next of previous to temp of previous (temp → next → previous
= temp → previous) and delete temp (free(temp)).
Displaying a
Double Linked List
We can use the following steps to display the
elements of a double linked list...
- Step
1: Check whether list is Empty (head == NULL)
- Step
2: If it is Empty, then display 'List is Empty!!!' and terminate the function.
- Step
3: If it is not Empty,
then define a Node pointer 'temp' and initialize with head.
- Step
4: Display 'NULL <--- '.
- Step
5: Keep displaying temp → data with an arrow (<===>) until temp reaches
to the last node
- Step
6: Finally, display temp → data with arrow pointing to NULL (temp → data ---> NULL).
