Write an algorithm to delete a node from end OF a doubly linked list

Deletion at beginning

Deletion in doubly linked list at the beginning is the simplest operation. We just need to copy the head pointer to pointer ptr and shift the head pointer to its next.

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Deletion at beginning
Delete a node in a Doubly Linked List
C Program For Deleting A Node In A Doubly Linked List
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now make the prev of this new head node point to NULL. This will be done by using the following statements.

Now free the pointer ptr by using the free function.

Delete a node in a Doubly Linked List

Pre-requisite: Doubly Link List Set 1| Introduction and Insertion

Write a function to delete a given node in a doubly-linked list.
Original Doubly Linked List

Write an algorithm to delete a node from end OF a doubly linked list

C Program For Deleting A Node In A Doubly Linked List

Pre-requisite: Doubly Link List Set 1| Introduction and Insertion

Write a function to delete a given node in a doubly-linked list.
Original Doubly Linked List

Recommended: Please solve it on “PRACTICE” first, before moving on to the solution.

Approach: The deletion of a node in a doubly-linked list can be divided into three main categories:

After the deletion of the head node.

After the deletion of the middle node.

After the deletion of the last node.

All three mentioned cases can be handled in two steps if the pointer of the node to be deleted and the head pointer is known.

If the node to be deleted is the head node then make the next node as head.
If a node is deleted, connect the next and previous node of the deleted node.

Algorithm

Let the node to be deleted be del.
If node to be deleted is head node, then change the head pointer to next current head.

if headnode == del then headnode = del.nextNode

Set next of previous to del, if previous to del exists.

if del.nextNode != none del.nextNode.previousNode = del.previousNode

Set prev of next to del, if next to del exists.

if del.previousNode != none del.previousNode.nextNode = del.next

// C program to implement 
// the above approach 
#include  
#include  

// A node of the doubly linked list 

struct Node
{ 

int data;

struct Node* next;

struct Node* prev;
}; 

/* Function to delete a node in a Doubly 

Linked List. head_ref --> pointer to

head node pointer. del --> pointer

to node to be deleted. */

void deleteNode(struct Node** head_ref,

struct Node* del)
{ 

// Base case

if (*head_ref == NULL || del == NULL)

return;

// If node to be deleted is head node

if (*head_ref == del)

*head_ref = del->next;

/* Change next only if node to be deleted

is NOT the last node */

if (del->next != NULL)

del->next->prev = del->prev;

/* Change prev only if node to be deleted

is NOT the first node */

if (del->prev != NULL)

del->prev->next = del->next;

// Finally, free the memory occupied by del

free(del);

return;
} 

// UTILITY FUNCTIONS 
/* Function to insert a node at the 

beginning of the Doubly Linked List */

void push(struct Node** head_ref,

int new_data)
{ 

// Allocate node

struct Node* new_node =

(struct Node*)malloc(sizeof(struct Node));

// Put in the data

new_node->data = new_data;

/* Since we are adding at the beginning,

prev is always NULL */

new_node->prev = NULL;

// Link the old list off the new node

new_node->next = (*head_ref);

// Change prev of head node to new node

if ((*head_ref) != NULL)

(*head_ref)->prev = new_node;

// Move the head to point to the new node

(*head_ref) = new_node;
} 

/* Function to print nodes in a given doubly 

linked list. This function is same as

printList() of singly linked list */

void printList(struct Node* node)
{ 

while (node != NULL)

{

printf("%d ", node->data);

node = node->next;

}
} 

// Driver code 

int main()
{ 

// Start with the empty list

struct Node* head = NULL;

/* Let us create the doubly

linked list 10<->8<->4<->2 */

push(&head, 2);

push(&head, 4);

push(&head, 8);

push(&head, 10);

printf(

"Original Linked list ");

printList(head);

/* Delete nodes from the doubly

linked list */

// Delete first node

deleteNode(&head, head);

// Delete middle node

deleteNode(&head, head->next);

// Delete last node

deleteNode(&head, head->next);

/* Modified linked list will be

NULL<-8->NULL */

printf(

"Modified Linked list ");

printList(head);

getchar();
}

Output:

Original Linked list 10 8 4 2 Modified Linked list 8

Complexity Analysis:

Time Complexity: O(1).
Since traversal of the linked list is not required so the time complexity is constant.
Space Complexity: O(1).
As no extra space is required, so the space complexity is constant.

Please refer complete article on Delete a node in a Doubly Linked List for more details!

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Write an algorithm to delete a node from end OF a doubly linked list

Deletion at beginning

Delete a node in a Doubly Linked List

C Program For Deleting A Node In A Doubly Linked List

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