Deletion in Doubly Circular Linked List

Last Updated : 10 Jan, 2023

We have discussed the doubly circular linked list introduction and its insertion.
Let us formulate the problem statement to understand the deletion process. Given a ‘key’, delete the first occurrence of this key in the circular doubly linked list.

Algorithm:

Case 1: Empty List(start = NULL)

If the list is empty, simply return it.

Case 2: The List initially contains some nodes, start points at the first node of the List

If the list is not empty, then we define two pointers curr and prev_1 and initialize the pointer curr points to the first node of the list, and prev_1 = NULL.
Traverse the list using the curr pointer to find the node to be deleted and before moving from curr to the next node, every time set prev_1 = curr.
If the node is found, check if it is the only node in the list. If yes, set start = NULL and free the node pointing by curr.
If the list has more than one node, check if it is the first node of the list. The condition to check this is (curr == start). If yes, then move prev_1 to the last node(prev_1 = start -> prev). After prev_1 reaches the last node, set start = start -> next and prev_1 -> next = start and start -> prev = prev_1. Free the node pointing by curr.
If curr is not the first node, we check if it is the last node in the list. The condition to check this is (curr -> next == start). If yes, set prev_1 -> next = start and start -> prev = prev_1. Free the node pointing by curr.
If the node to be deleted is neither the first node nor the last node, declare one more pointer temp and initialize the pointer temp points to the next of curr pointer (temp = curr->next). Now set, prev_1 -> next = temp and temp ->prev = prev_1. Free the node pointing by curr.

If the given key(Say 4) matches with the first node of the list(Step 4):

Delete_first_node

If the given key(Say 8) matches with the last node of the list(Step 5):

Delete_last_node

If the given key(Say 6) matches with the middle node of the list(Step 6):

Delete_middle_node

Implementation:

C++

// C++ program to delete a given key from
// circular doubly linked list.
#include <bits/stdc++.h>
using namespace std;

// Structure of a Node
struct Node {
    int data;
    struct Node* next;
    struct Node* prev;
};

// Function to insert node in the list
void insert(struct Node** start, int value)
{
    // If the list is empty, create a single node
    // circular and doubly list
    if (*start == NULL) {
        struct Node* new_node = new Node;
        new_node->data = value;
        new_node->next = new_node->prev = new_node;
        *start = new_node;
        return;
    }

    // If list is not empty

    /* Find last node */
    Node* last = (*start)->prev;

    // Create Node dynamically
    struct Node* new_node = new Node;
    new_node->data = value;

    // Start is going to be next of new_node
    new_node->next = *start;

    // Make new node previous of start
    (*start)->prev = new_node;

    // Make last previous of new node
    new_node->prev = last;

    // Make new node next of old last
    last->next = new_node;
}

// Function to delete a given node from the list
void deleteNode(struct Node** start, int key)
{
    // If list is empty
    if (*start == NULL)
        return;

    // Find the required node
    // Declare two pointers and initialize them
    struct Node *curr = *start, *prev_1 = NULL;
    while (curr->data != key) {
        // If node is not present in the list
        if (curr->next == *start) {
            printf("\nList doesn't have node with value = %d", key);
            return;
        }

        prev_1 = curr;
        curr = curr->next;
    }

    // Check if node is the only node in list
    if (curr->next == *start && prev_1 == NULL) {
        (*start) = NULL;
        free(curr);
        return;
    }

    // If list has more than one node,
    // check if it is the first node
    if (curr == *start) {
        // Move prev_1 to last node
        prev_1 = (*start)->prev;

        // Move start ahead
        *start = (*start)->next;

        // Adjust the pointers of prev_1 and start node
        prev_1->next = *start;
        (*start)->prev = prev_1;
        free(curr);
    }

    // check if it is the last node
    else if (curr->next == *start) {
        // Adjust the pointers of prev_1 and start node
        prev_1->next = *start;
        (*start)->prev = prev_1;
        free(curr);
    }
    else {
        // create new pointer, points to next of curr node
        struct Node* temp = curr->next;

        // Adjust the pointers of prev_1 and temp node
        prev_1->next = temp;
        temp->prev = prev_1;
        free(curr);
    }
}

// Function to display list elements
void display(struct Node* start)
{
    struct Node* temp = start;

    while (temp->next != start) {
        printf("%d ", temp->data);
        temp = temp->next;
    }
    printf("%d ", temp->data);
}

// Driver program to test above functions
int main()
{
    // Start with the empty list
    struct Node* start = NULL;

    // Created linked list will be 4->5->6->7->8
    insert(&start, 4);
    insert(&start, 5);
    insert(&start, 6);
    insert(&start, 7);
    insert(&start, 8);

    printf("List Before Deletion: ");
    display(start);

    // Delete the node which is not present in list
    deleteNode(&start, 9);
    printf("\nList After Deletion: ");
    display(start);

    // Delete the first node
    deleteNode(&start, 4);
    printf("\nList After Deleting %d: ", 4);
    display(start);

    // Delete the last node
    deleteNode(&start, 8);
    printf("\nList After Deleting %d: ", 8);
    display(start);

    // Delete the middle node
    deleteNode(&start, 6);
    printf("\nList After Deleting %d: ", 6);
    display(start);

    return 0;
}

Java

// Java program to delete a given key from
// circular doubly linked list.
import java.util.*;
import java.io.*;

class GFG {

    // structure of a Node
    static class Node {
        int data;
        Node next;
        Node prev;
    };

    // Function to insert node in the list
    static Node insert(Node start, int value)
    {
        // If the list is empty, create a single node
        // circular and doubly list
        if (start == null) {
            Node new_node = new Node();
            new_node.data = value;
            new_node.next = new_node.prev = new_node;
            start = new_node;
            return start;
        }

        // If list is not empty

        // Find last node /
        Node last = (start).prev;

        // Create Node dynamically
        Node new_node = new Node();
        new_node.data = value;

        // Start is going to be next of new_node
        new_node.next = start;

        // Make new node previous of start
        (start).prev = new_node;

        // Make last previous of new node
        new_node.prev = last;

        // Make new node next of old last
        last.next = new_node;
        return start;
    }

    // Function to delete a given node from the list
    static Node deleteNode(Node start, int key)
    {
        // If list is empty
        if (start == null)
            return null;

        // Find the required node
        // Declare two pointers and initialize them
        Node curr = start, prev_1 = null;
        while (curr.data != key) {
            // If node is not present in the list
            if (curr.next == start) {
                System.out.printf("\nList doesn't have node with value = %d", key);
                return start;
            }

            prev_1 = curr;
            curr = curr.next;
        }

        // Check if node is the only node in list
        if (curr.next == start && prev_1 == null) {
            (start) = null;
            return start;
        }

        // If list has more than one node,
        // check if it is the first node
        if (curr == start) {
            // Move prev_1 to last node
            prev_1 = (start).prev;

            // Move start ahead
            start = (start).next;

            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }

        // check if it is the last node
        else if (curr.next == start) {
            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }
        else {
            // create new pointer, points to next of curr node
            Node temp = curr.next;

            // Adjust the pointers of prev_1 and temp node
            prev_1.next = temp;
            temp.prev = prev_1;
        }
        return start;
    }

    // Function to display list elements
    static void display(Node start)
    {
        Node temp = start;

        while (temp.next != start) {
            System.out.printf("%d ", temp.data);
            temp = temp.next;
        }
        System.out.printf("%d ", temp.data);
    }

    // Driver program to test above functions
    public static void main(String args[])
    {
        // Start with the empty list
        Node start = null;

        // Created linked list will be 4.5.6.7.8
        start = insert(start, 4);
        start = insert(start, 5);
        start = insert(start, 6);
        start = insert(start, 7);
        start = insert(start, 8);

        System.out.printf("List Before Deletion: ");
        display(start);

        // Delete the node which is not present in list
        start = deleteNode(start, 9);
        System.out.printf("\nList After Deletion: ");
        display(start);

        // Delete the first node
        start = deleteNode(start, 4);
        System.out.printf("\nList After Deleting %d: ", 4);
        display(start);

        // Delete the last node
        start = deleteNode(start, 8);
        System.out.printf("\nList After Deleting %d: ", 8);
        display(start);

        // Delete the middle node
        start = deleteNode(start, 6);
        System.out.printf("\nList After Deleting %d: ", 6);
        display(start);
    }
}

// This code is contributed by Arnab Kundu

Python3

# Python3 program to delete a given key from
# circular doubly linked list.

# structure of a node of linked list 
class Node: 
    def __init__(self, data): 
        self.data = data 
        self.next = None
        self.prev = None

def insert( start, value):
    
    # If the list is empty, create a single node
    # circular and doubly list
    if (start == None): 
        new_node = Node(0)
        new_node.data = value
        new_node.next = new_node.prev = new_node
        start = new_node
        return start
        
    # If list is not empty

    # Find last node /
    last = (start).prev

    # Create Node dynamically
    new_node = Node(0)
    new_node.data = value

    # Start is going to be next of new_node
    new_node.next = start

    # Make new node previous of start
    (start).prev = new_node

    # Make last previous of new node
    new_node.prev = last

    # Make new node next of old last
    last.next = new_node
    return start
    
# Function to delete a given node
# from the list
def deleteNode(start, key):
    
    # If list is empty
    if (start == None):
        return None

    # Find the required node
    # Declare two pointers and initialize them
    curr = start
    prev_1 = None
    while (curr.data != key) :
        
        # If node is not present in the list
        if (curr.next == start) :
            print ("List doesn't have node", 
                       "with value = ", key)
            return start
            
        prev_1 = curr
        curr = curr.next
        
    # Check if node is the only node in list
    if (curr.next == start and prev_1 == None) :
        (start) = None
        return start
        
    # If list has more than one node,
    # check if it is the first node
    if (curr == start) :
        
        # Move prev_1 to last node
        prev_1 = (start).prev

        # Move start ahead
        start = (start).next

        # Adjust the pointers of prev_1 
        # and start node
        prev_1.next = start
        (start).prev = prev_1
        
    # check if it is the last node
    elif (curr.next == start) :
        
        # Adjust the pointers of prev_1 
        # and start node
        prev_1.next = start
        (start).prev = prev_1
        
    else :
        
        # create new pointer,
        # points to next of curr node
        temp = curr.next

        # Adjust the pointers of prev_1
        # and temp node
        prev_1.next = temp
        temp.prev = prev_1
        
    return start
    
# Function to display list elements
def display(start):
    
    temp = start

    while (temp.next != start) :
        print (temp.data, end = " ") 
        temp = temp.next
        
    print (temp.data)
    
# Driver Code 
if __name__=='__main__': 
    
    # Start with the empty list
    start = None

    # Created linked list will be 4.5.6.7.8
    start = insert(start, 4)
    start = insert(start, 5)
    start = insert(start, 6)
    start = insert(start, 7)
    start = insert(start, 8)

    print ("List Before Deletion: ")
    display(start)

    # Delete the node which is not present in list
    start = deleteNode(start, 9)
    print ("List After Deletion: ")
    display(start)

    # Delete the first node
    start = deleteNode(start, 4)
    print ("List After Deleting", 4)
    display(start)

    # Delete the last node
    start = deleteNode(start, 8)
    print ("List After Deleting ", 8)
    display(start)

    # Delete the middle node
    start = deleteNode(start, 6)
    print ("List After Deleting ", 6)
    display(start)
    
# This code is contributed by Arnab Kundu

// C# program to delete a given key from
// circular doubly linked list.
using System;

class GFG {

    // structure of a Node
    public class Node {
        public int data;
        public Node next;
        public Node prev;
    };

    // Function to insert node in the list
    static Node insert(Node start, int value)
    {
        // If the list is empty, create a single node
        // circular and doubly list
        Node new_node = new Node();
        if (start == null) {

            new_node.data = value;
            new_node.next = new_node.prev = new_node;
            start = new_node;
            return start;
        }

        // If list is not empty

        // Find last node /
        Node last = (start).prev;

        // Create Node dynamically
        new_node = new Node();
        new_node.data = value;

        // Start is going to be next of new_node
        new_node.next = start;

        // Make new node previous of start
        (start).prev = new_node;

        // Make last previous of new node
        new_node.prev = last;

        // Make new node next of old last
        last.next = new_node;
        return start;
    }

    // Function to delete a given node from the list
    static Node deleteNode(Node start, int key)
    {
        // If list is empty
        if (start == null)
            return null;

        // Find the required node
        // Declare two pointers and initialize them
        Node curr = start, prev_1 = null;
        while (curr.data != key) {
            // If node is not present in the list
            if (curr.next == start) {
                Console.Write("\nList doesn't have node with value = {0}", key);
                return start;
            }

            prev_1 = curr;
            curr = curr.next;
        }

        // Check if node is the only node in list
        if (curr.next == start && prev_1 == null) {
            (start) = null;
            return start;
        }

        // If list has more than one node,
        // check if it is the first node
        if (curr == start) {
            // Move prev_1 to last node
            prev_1 = (start).prev;

            // Move start ahead
            start = (start).next;

            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }

        // check if it is the last node
        else if (curr.next == start) {
            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }
        else {
            // create new pointer, points to next of curr node
            Node temp = curr.next;

            // Adjust the pointers of prev_1 and temp node
            prev_1.next = temp;
            temp.prev = prev_1;
        }
        return start;
    }

    // Function to display list elements
    static void display(Node start)
    {
        Node temp = start;

        while (temp.next != start) {
            Console.Write("{0} ", temp.data);
            temp = temp.next;
        }
        Console.Write("{0} ", temp.data);
    }

    // Driver code
    public static void Main(String[] args)
    {
        // Start with the empty list
        Node start = null;

        // Created linked list will be 4.5.6.7.8
        start = insert(start, 4);
        start = insert(start, 5);
        start = insert(start, 6);
        start = insert(start, 7);
        start = insert(start, 8);

        Console.Write("List Before Deletion: ");
        display(start);

        // Delete the node which is not present in list
        start = deleteNode(start, 9);
        Console.Write("\nList After Deletion: ");
        display(start);

        // Delete the first node
        start = deleteNode(start, 4);
        Console.Write("\nList After Deleting {0}: ", 4);
        display(start);

        // Delete the last node
        start = deleteNode(start, 8);
        Console.Write("\nList After Deleting {0}: ", 8);
        display(start);

        // Delete the middle node
        start = deleteNode(start, 6);
        Console.Write("\nList After Deleting {0}: ", 6);
        display(start);
    }
}

// This code has been contributed by 29AjayKumar

JavaScript

<script>
    // javascript program to delete a given key from
    // circular doubly linked list.   
      // structure of a Node
    class Node {
        constructor() {
            this.data = 0;
            this.prev = null;
            this.next = null;
        }
    }

    // Function to insert node in the list
    function insert(start , value)
    {
        // If the list is empty, create a single node
        // circular and doubly list
        if (start == null) {
            var new_node = new Node();
            new_node.data = value;
            new_node.next = new_node.prev = new_node;
            start = new_node;
            return start;
        }

        // If list is not empty

        // Find last node /
        var last = (start).prev;

        // Create Node dynamically
        var new_node = new Node();
        new_node.data = value;

        // Start is going to be next of new_node
        new_node.next = start;

        // Make new node previous of start
        (start).prev = new_node;

        // Make last previous of new node
        new_node.prev = last;

        // Make new node next of old last
        last.next = new_node;
        return start;
    }

    // Function to delete a given node from the list
    function deleteNode(start , key) {
        // If list is empty
        if (start == null)
            return null;

        // Find the required node
        // Declare two pointers and initialize them
        var curr = start, prev_1 = null;
        while (curr.data != key) {
            // If node is not present in the list
            if (curr.next == start) {
                document.write("<br/>List doesn't have node with value = "+ key);
                return start;
            }

            prev_1 = curr;
            curr = curr.next;
        }

        // Check if node is the only node in list
        if (curr.next == start && prev_1 == null) {
            (start) = null;
            return start;
        }

        // If list has more than one node,
        // check if it is the first node
        if (curr == start) {
            // Move prev_1 to last node
            prev_1 = (start).prev;

            // Move start ahead
            start = (start).next;

            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }

        // check if it is the last node
        else if (curr.next == start) {
            // Adjust the pointers of prev_1 and start node
            prev_1.next = start;
            (start).prev = prev_1;
        }
        else {
            // create new pointer, points to next of curr node
            var temp = curr.next;

            // Adjust the pointers of prev_1 and temp node
            prev_1.next = temp;
            temp.prev = prev_1;
        }
        return start;
    }

    // Function to display list elements
    function display(start)
    {
        var temp = start;

        while (temp.next != start) {
            document.write( temp.data+" ");
            temp = temp.next;
        }
        document.write( temp.data+" ");
    }

        // Driver program to test above functions
    
        // Start with the empty list
        var start = null;

        // Created linked list will be 4.5.6.7.8
        start = insert(start, 4);
        start = insert(start, 5);
        start = insert(start, 6);
        start = insert(start, 7);
        start = insert(start, 8);

        document.write("List Before Deletion: ");
        display(start);

        // Delete the node which is not present in list
        start = deleteNode(start, 9);
        document.write("<br/>List After Deletion: ");
        display(start);

        // Delete the first node
        start = deleteNode(start, 4);
        document.write("<br/>List After Deleting 4: ");
        display(start);

        // Delete the last node
        start = deleteNode(start, 8);
        document.write("<br/>List After Deleting 8: ");
        display(start);

        // Delete the middle node
        start = deleteNode(start, 6);
        document.write("<br/>List After Deleting 6: ");
        display(start);

// This code contributed by aashish1995 
</script>

Output

List Before Deletion: 4 5 6 7 8 
List doesn't have node with value = 9
List After Deletion: 4 5 6 7 8 
List After Deleting 4: 5 6 7 8 
List After Deleting 8: 5 6 7 
List After Deleting 6: 5 7

Time Complexity: O(n), as we are using a loop to traverse n times (for deletion and displaying the linked list). Where n is the number of nodes in the linked list.
Auxiliary Space: O(1), as we are not using any extra space.

Insertion in Doubly Circular Linked List

Akash Gupta

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Deletion in Doubly Circular Linked List

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