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

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 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#

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

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

    // 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("Created DLL is: ");
        dll.printlist(dll.head);

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

        // List after deleting first node
        // 8->4->2
        Console.Write(
        "List after deleting first node: ");
        dll.printlist(dll.head);

        // Deleting middle node from 8->4->2
        dll.deleteNode(dll.head.next);

        Console.Write(
        "List after Deleting middle node: ");
        dll.printlist(dll.head);
    }
}
// This code is contributed by PrinciRaj1992

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!