Delete a node in a Doubly Linked List

Write a function to delete a given node in a doubly-linked list. 

Example:

Input: DLL = 2->45->3->1, Node = 45
Output:  2->3->1

Input: DLL = 2->45->3->1, Node = 1
Output:  2->45->3

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.

1. If the node to be deleted is the head node then make the next node as head.
2. 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 prev of next to del, if next to del exists.

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

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

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

Below is the implementation of the above approach:

C++

// C++ program to delete a node from
// Doubly Linked List
#include <bits/stdc++.h>
using namespace std;

/* a node of the doubly linked list */
class Node
{
    public:
    int data;
    Node* next;
    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(Node** head_ref, 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(Node** head_ref, int new_data)
{
    /* allocate node */
    Node* new_node = new 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 of 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(Node* node)
{
    while (node != NULL)
    {
        cout << node->data << " ";
        node = node->next;
    }
}

/* Driver code*/
int main()
{
    /* Start with the empty list */
    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);

    cout << "Original Linked list ";
    printList(head);

    /* delete nodes from the doubly linked list */
    deleteNode(&head, head); /*delete first node*/
    deleteNode(&head, head->next); /*delete middle node*/
    deleteNode(&head, head->next); /*delete last node*/

    /* Modified linked list will be NULL<-8->NULL */
    cout << "\nModified Linked list ";
    printList(head);

    return 0;
}

// This code is contributed by rathbhupendra

C

#include <stdio.h>
#include <stdlib.h>

/* 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 of 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 program to test above functions*/
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("\n Original Linked list ");
    printList(head);

    /* delete nodes from the doubly linked list */
    deleteNode(&head, head); /*delete first node*/
    deleteNode(&head, head->next); /*delete middle node*/
    deleteNode(&head, head->next); /*delete last node*/

    /* Modified linked list will be NULL<-8->NULL */
    printf("\n Modified Linked list ");
    printList(head);

    getchar();
}

Java

// Java program to delete a node from
// Doubly Linked List

// Class for Doubly Linked List
public class DLL {
    Node head; // head of list

    /* Doubly Linked list Node*/
    class Node {
        int data;
        Node prev;
        Node next;

        // Constructor to create a new node
        // next and prev is by default initialized
        // as null
        Node(int d) { data = d; }
    }

    // Adding a node at the front of the list
    public void push(int new_data)
    {
        // 1. allocate node
        // 2. put in the data
        Node new_Node = new Node(new_data);

        // 3. Make next of new node as head
        // and previous as NULL
        new_Node.next = head;
        new_Node.prev = null;

        // 4. change prev of head node to new node
        if (head != null)
            head.prev = new_Node;

        // 5. move the head to point to the new node
        head = new_Node;
    }

    // This function prints contents of linked list
    // starting from the given node
    public void printlist(Node node)
    {
        Node last = null;

        while (node != null) {
            System.out.print(node.data + " ");
            last = node;
            node = node.next;
        }

        System.out.println();
    }

    // Function to delete a node in a Doubly Linked List.
    // head_ref --> pointer to head node pointer.
    // del --> data of node to be deleted.
    void deleteNode(Node del)
    {

        // Base case
        if (head == null || del == null) {
            return;
        }

        // If node to be deleted is head node
        if (head == del) {
            head = 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
        return;
    }

    // Driver Code
    public static void main(String[] args)
    {
        // Start with the empty list
        DLL dll = new DLL();

        // Insert 2. So linked list becomes 2->NULL
        dll.push(2);

        // Insert 4. So linked list becomes 4->2->NULL
        dll.push(4);

        // Insert 8. So linked list becomes 8->4->2->NULL
        dll.push(8);

        // Insert 10. So linked list becomes
        // 10->8->4->2->NULL
        dll.push(10);

        System.out.print("Original Linked list ");
        dll.printlist(dll.head);


        dll.deleteNode(dll.head); /*delete first node*/
        dll.deleteNode(dll.head.next); /*delete middle node*/
        dll.deleteNode(dll.head.next); /*delete last node*/

        System.out.print(
            "\nModified Linked list ");
        dll.printlist(dll.head);
    }
}

Python3

# Program to delete a node in a doubly-linked list

# for Garbage collection
import gc

# A node of the doubly linked list
class Node:

    # Constructor to create a new node
    def __init__(self, data):
        self.data = data
        self.next = None
        self.prev = None

class DoublyLinkedList:
     # Constructor for empty Doubly Linked List
    def __init__(self):
        self.head = None

   # Function to delete a node in a Doubly Linked List.
   # head_ref --> pointer to head node pointer.
   # dele --> pointer to node to be deleted

    def deleteNode(self, dele):

        # Base Case
        if self.head is None or dele is None:
            return

        # If node to be deleted is head node
        if self.head == dele:
            self.head = dele.next

        # Change next only if node to be deleted is NOT
        # the last node
        if dele.next is not None:
            dele.next.prev = dele.prev

        # Change prev only if node to be deleted is NOT
        # the first node
        if dele.prev is not None:
            dele.prev.next = dele.next
        # Finally, free the memory occupied by dele
        # Call python garbage collector
        gc.collect()


    # Given a reference to the head of a list and an
    # integer, inserts a new node on the front of list
    def push(self, new_data):

        # 1. Allocates node
        # 2. Put the data in it
        new_node = Node(new_data)

        # 3. Make next of new node as head and
        # previous as None (already None)
        new_node.next = self.head

        # 4. change prev of head node to new_node
        if self.head is not None:
            self.head.prev = new_node

        # 5. move the head to point to the new node
        self.head = new_node


    def printList(self, node):
        while(node is not None):
            print(node.data,end=' ')
            node = node.next


# Driver program to test the above functions

# Start with empty list
dll = DoublyLinkedList()

# Let us create the doubly linked list 10<->8<->4<->2
dll.push(2);
dll.push(4);
dll.push(8);
dll.push(10);

print ("\n Original Linked List",end=' ')
dll.printList(dll.head)

# delete nodes from doubly linked list
dll.deleteNode(dll.head)
dll.deleteNode(dll.head.next)
dll.deleteNode(dll.head.next)
# Modified linked list will be NULL<-8->NULL
print("\n Modified Linked List",end=' ')
dll.printList(dll.head)

# This code is contributed by Nikhil Kumar Singh(nickzuck_007)

C#

// C# program to delete a node from
// Doubly Linked List
using System;

// Class for Doubly Linked List
public class DLL
{
    Node head; // head of list

    /* Doubly Linked list Node*/
    public class Node
    {
        public int data;
        public Node prev;
        public Node next;

        // Constructor to create a new node
        // next and prev is by default
        // initialized as null
        public Node(int d) { data = d; }
    }

    // Adding a node at the front of the list
    public void push(int new_data)
    {
        // 1. allocate node
        // 2. put in the data
        Node new_Node = new Node(new_data);

        // 3. Make next of new node as head
        // and previous as NULL
        new_Node.next = head;
        new_Node.prev = null;

        // 4. change prev of head node to new node
        if (head != null)
            head.prev = new_Node;

        // 5. move the head to point to the new node
        head = new_Node;
    }

    // This function prints contents of linked list
    // starting from the given node
    public void printlist(Node node)
    {

        while (node != null)
        {
            Console.Write(node.data + " ");
            node = node.next;
        }

        Console.WriteLine();
    }

    // Function to delete a node in a Doubly Linked List.
    // head_ref --> pointer to head node pointer.
    // del --> data of node to be deleted.
    void deleteNode(Node del)
    {

        // Base case
        if (head == null || del == null)
        {
            return;
        }

        // If node to be deleted is head node
        if (head == del)
        {
            head = 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
        return;
    }

    // Driver Code
    public static void Main()
    {
        // Start with the empty list
        DLL dll = new DLL();

        // Insert 2. So linked list becomes 2->NULL
        dll.push(2);

        // Insert 4. So linked list becomes 4->2->NULL
        dll.push(4);

        // Insert 8. So linked list becomes 8->4->2->NULL
        dll.push(8);

        // Insert 10. So linked list becomes 10->8->4->2->NULL
        dll.push(10);

        Console.Write("Original Linked list ");
        dll.printlist(dll.head);

        // Deleting first node
        dll.deleteNode(dll.head);

        dll.deleteNode(dll.head.next);

          dll.deleteNode(dll.head.next);

          Console.Write("Modified Linked list ");
        dll.printlist(dll.head);
    }
}
// This code is contributed by PrinciRaj1992

Javascript

<script>

// Javascript program to delete a node from
// Doubly Linked List

// Class for Doubly Linked List
var head; // head of list

    /* Doubly Linked list Node */
    class Node {

        // Constructor to create a new node
        // next and prev is by default initialized
        // as null
        constructor(val) {
            this.data = val;
            this.prev = null;
            this.next = null;
        }
    }

    // Adding a node at the front of the list
    function push(new_data) {
        // 1. allocate node
        // 2. put in the data
         new_Node = new Node(new_data);

        // 3. Make next of new node as head
        // and previous as NULL
        new_Node.next = head;
        new_Node.prev = null;

        // 4. change prev of head node to new node
        if (head != null)
            head.prev = new_Node;

        // 5. move the head to point to the new node
        head = new_Node;
    }

    // This function prints contents of linked list
    // starting from the given node
    function printlist( node) {
         last = null;

        while (node != null) {
            document.write(node.data + " ");
            last = node;
            node = node.next;
        }

        document.write("<br/>");
    }

    // Function to delete a node in a Doubly Linked List.
    // head_ref --> pointer to head node pointer.
    // del --> data of node to be deleted.
    function deleteNode( del) {

        // Base case
        if (head == null || del == null) {
            return;
        }

        // If node to be deleted is head node
        if (head == del) {
            head = 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
        return;
    }

    // Driver Code

        // Start with the empty list

        // Insert 2. So linked list becomes 2->NULL
        push(2);

        // Insert 4. So linked list becomes 4->2->NULL
        push(4);

        // Insert 8. So linked list becomes 8->4->2->NULL
        push(8);

        // Insert 10. So linked list becomes 10->8->4->2->NULL
        push(10);

        document.write("Created DLL is: ");
        printlist(head);

        // Deleting first node
        deleteNode(head);
        deleteNode(head.next);
        deleteNode(head.next);

        document.write("Modified Linked list: ");
        printlist(head);


// This code is contributed by todaysgaurav

</script>

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.
• Auxiliary Space: O(1). 
  As no extra space is required, so the space complexity is constant.