Delete all occurrences of a given key in a doubly linked list

Given a doubly linked list and a key x. The problem is to delete all occurrences of the given key x from the doubly linked list.

Examples:

Algorithm:

delAllOccurOfGivenKey(head_ref, x)
      if head_ref == NULL
          return
      Initialize current = head_ref
      Declare next
      while current != NULL
           if current->data == x
               next = current->next
               deleteNode(head_ref, current)
               current = next
           else
               current = current->next

The algorithm for deleteNode(head_ref, current) (which deletes the node using the pointer to the node) is discussed in this post.

Implementation:

C++

/* C++ implementation to delete all occurrences
   of a given key in a doubly linked list */
#include <bits/stdc++.h>

using namespace std;

/* 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);
}

/* function to delete all occurrences of the given
    key 'x' */
void deleteAllOccurOfX(struct Node** head_ref, int x)
{
    /* if list is empty */
    if ((*head_ref) == NULL)
        return;

    struct Node* current = *head_ref;
    struct Node* next;

    /* traverse the list up to the end */
    while (current != NULL) {

        /* if node found with the value 'x' */
        if (current->data == x) {

            /* save current's next node in the
               pointer 'next' */
            next = current->next;

            /* delete the node pointed to by
              'current' */
            deleteNode(head_ref, current);

            /* update current */
            current = next;
        }

        /* else simply move to the next node */
        else
            current = current->next;
    }
}

/* 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 */
void printList(struct Node* head)
{
    /* if list is empty */
    if (head == NULL)
        cout << "Doubly Linked list empty";

    while (head != NULL) {
        cout << head->data << " ";
        head = head->next;
    }
}

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

    /* Create the doubly linked list:
           2<->2<->10<->8<->4<->2<->5<->2 */
    push(&head, 2);
    push(&head, 5);
    push(&head, 2);
    push(&head, 4);
    push(&head, 8);
    push(&head, 10);
    push(&head, 2);
    push(&head, 2);

    cout << "Original Doubly linked list:n";
    printList(head);

    int x = 2;

    /* delete all occurrences of 'x' */
    deleteAllOccurOfX(&head, x);

    cout << "\nDoubly linked list after deletion of "
         << x << ":n";
    printList(head);

    return 0;
}

Java

/* Java implementation to delete all occurrences
of a given key in a doubly linked list */
import java.util.*;
import java.io.*;

// a node of the doubly linked list
class Node
{
    int data;
    Node next, prev;
}

class GFG
{
    /* Function to delete a node in a Doubly Linked List.
        head_ref --> pointer to head node pointer.
        del --> pointer to node to be deleted. */
    static Node deleteNode(Node head, Node del)
    {
        // base case
        if (head == null || del == null)
            return null;

        /* 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;

        del = null;

        return head;
    }

    /* function to delete all occurrences of the given
        key 'x' */
    static Node deleteAllOccurOfX(Node head, int x)
    {
        // if list is empty
        if (head == null)
            return null;

        Node current = head;
        Node next;

        /* traverse the list up to the end */
        while (current != null)
        {
            // if node found with the value 'x'
            if (current.data == x)
            {

                /* save current's next node in the
                pointer 'next' */
                next = current.next;

                /* delete the node pointed to by
                'current' */
                head = deleteNode(head, current);

                /* update current */
                current = next;
            }

            /* else simply move to the next node */
            else
                current = current.next;

        }

        return head;

    }

    /* Function to insert a node at the beginning
        of the Doubly Linked List */
    static Node push (Node head, 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;

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

        // move the head to point to the new node
        head = new_node;

        return head;
    }

    /* Function to print nodes in a given doubly
        linked list */
    static void printList (Node temp)
    {
        if (temp == null)
            System.out.print("Doubly Linked list empty");

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

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

        /* Create the doubly linked list:
        2<->2<->10<->8<->4<->2<->5<->2 */
        head = push(head, 2);
        head = push(head, 5);
        head = push(head, 2);
        head = push(head, 4);
        head = push(head, 8);
        head = push(head, 10);
        head = push(head, 2);
        head = push(head, 2);

        System.out.println("Original Doubly linked list: ");
        printList(head);

        int x = 2;

        // delete all occurrences of 'x'
        head = deleteAllOccurOfX(head, x);
        System.out.println("\nDoubly linked list after deletion of" + x +":");
        printList(head);
    }
}

// This code is contributed by rachana soma

Python3

# Python3 implementation to delete all occurrences
# of a given key in a doubly linked list
import math

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

# Function to delete a node in a Doubly Linked List.
# head_ref --> pointer to head node pointer.
# del --> pointer to node to be deleted.
def deleteNode(head, delete):
    # base case
    if (head == None or delete == None):
        return None

    # If node to be deleted is head node
    if (head == delete):
        head = delete.next

    # Change next only if node to be deleted
    # is NOT the last node
    if (delete.next != None):
        delete.next.prev = delete.prev

    # Change prev only if node to be deleted
    # is NOT the first node
    if (delete.prev != None):
        delete.prev.next = delete.next

    # Finally, free the memory occupied by del
    # free(del)
    delete = None
    return head

# function to delete all occurrences of the given
# key 'x'
def deleteAllOccurOfX(head, x):
    # if list is empty
    if (head == None):
        return

    current = head

    # traverse the list up to the end
    while (current != None):

        # if node found with the value 'x'
        if (current.data == x):

            # save current's next node in the
            #pointer 'next'
            next = current.next

            # delete the node pointed to by
            # 'current'
            head = deleteNode(head, current)

            # update current
            current = next

        # else simply move to the next node
        else:
            current = current.next

    return head

# Function to insert a node at the beginning
# of the Doubly Linked List
def push(head,new_data):
    # allocate node
    new_node = Node(new_data)

    # put in the data
    new_node.data = new_data

    # since we are adding at the beginning,
    #prev is always None
    new_node.prev = None

    # link the old list of the new node
    new_node.next = head

    # change prev of head node to new node
    if (head != None):
        head.prev = new_node

    # move the head to point to the new node
    head = new_node
    return head

# Function to print nodes in a given doubly
# linked list
def printList(head):
    # if list is empty
    if (head == None):
        print("Doubly Linked list empty")

    while (head != None) :
        print(head.data,end=" ")
        head = head.next

# Driver functions
if __name__=='__main__':
    # Start with the empty list
    head = None

    # Create the doubly linked list:
    #     2<->2<->10<->8<->4<->2<->5<->2
    head = push(head, 2)
    head = push(head, 5)
    head = push(head, 2)
    head = push(head, 4)
    head = push(head, 8)
    head = push(head, 10)
    head = push(head, 2)
    head = push(head, 2)

    print("Original Doubly linked list:")
    printList(head)

    x = 2

    # delete all occurrences of 'x'
    head = deleteAllOccurOfX(head, x)

    print("\nDoubly linked list after deletion of ",x,":")
    printList(head)

# This article contributed by Srathore

C#

/* C# implementation to delete all occurrences
of a given key in a doubly linked list */
using System;
using System.Collections;

// a node of the doubly linked list
public class Node
{
    public int data;
    public Node next, prev;
}

class GFG
{
    /* Function to delete a node in a Doubly Linked List.
        head_ref --> pointer to head node pointer.
        del --> pointer to node to be deleted. */
    static Node deleteNode(Node head, Node del)
    {
        // base case
        if (head == null || del == null)
            return null;

        /* 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;

        del = null;

        return head;
    }

    /* function to delete all occurrences of the given
        key 'x' */
    static Node deleteAllOccurOfX(Node head, int x)
    {
        // if list is empty
        if (head == null)
            return null;

        Node current = head;
        Node next;

        /* traverse the list up to the end */
        while (current != null)
        {
            // if node found with the value 'x'
            if (current.data == x)
            {

                /* save current's next node in the
                pointer 'next' */
                next = current.next;

                /* delete the node pointed to by
                'current' */
                head = deleteNode(head, current);

                /* update current */
                current = next;
            }

            /* else simply move to the next node */
            else
                current = current.next;

        }

        return head;

    }

    /* Function to insert a node at the beginning
        of the Doubly Linked List */
    static Node push (Node head, 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;

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

        // move the head to point to the new node
        head = new_node;

        return head;
    }

    /* Function to print nodes in a given doubly
        linked list */
    static void printList (Node temp)
    {
        if (temp == null)
            Console.Write("Doubly Linked list empty");

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

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

        /* Create the doubly linked list:
        2<->2<->10<->8<->4<->2<->5<->2 */
        head = push(head, 2);
        head = push(head, 5);
        head = push(head, 2);
        head = push(head, 4);
        head = push(head, 8);
        head = push(head, 10);
        head = push(head, 2);
        head = push(head, 2);

        Console.WriteLine("Original Doubly linked list: ");
        printList(head);

        int x = 2;

        // delete all occurrences of 'x'
        head = deleteAllOccurOfX(head, x);
        Console.WriteLine("\nDoubly linked list after deletion of" + x +":");
        printList(head);
    }
}

// This code is contributed by Arnab Kundu

Javascript

<script>
/* javascript implementation to delete all occurrences
of a given key in a doubly linked list */
// a node of the doubly linked list
 class Node {
        constructor(val) {
            this.data = val;
            this.prev = null;
            this.next = null;
        }
    }
 /*
     * Function to delete a node in a Doubly Linked List. head_ref --> pointer to
     * head node pointer. del --> pointer to node to be deleted.
     */
    function deleteNode(head,  del) {
        // base case
        if (head == null || del == null)
            return null;

        /* 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;

        del = null;

        return head;
    }

    /*
     * function to delete all occurrences of the given key 'x'
     */
    function deleteAllOccurOfX(head , x) {
        // if list is empty
        if (head == null)
            return null;

var current = head;
var next;

        /* traverse the list up to the end */
        while (current != null) {
            // if node found with the value 'x'
            if (current.data == x) {

                /*
                 * save current's next node in the pointer 'next'
                 */
                next = current.next;

                /*
                 * delete the node pointed to by 'current'
                 */
                head = deleteNode(head, current);

                /* update current */
                current = next;
            }

            /* else simply move to the next node */
            else
                current = current.next;

        }

        return head;

    }

    /*
     * Function to insert a node at the beginning of the Doubly Linked List
     */
    function push(head , new_data) {
        // allocate node
var 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;

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

        // move the head to point to the new node
        head = new_node;

        return head;
    }

    /*
     * Function to print nodes in a given doubly linked list
     */
    function printList(temp) {
        if (temp == null)
            document.write("Doubly Linked list empty");

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

    // Driver code

        // Start with the empty list
var head = null;

        /*
         * Create the doubly linked list: 2<->2<->10<->8<->4<->2<->5<->2
         */
        head = push(head, 2);
        head = push(head, 5);
        head = push(head, 2);
        head = push(head, 4);
        head = push(head, 8);
        head = push(head, 10);
        head = push(head, 2);
        head = push(head, 2);

        document.write("Original Doubly linked list: <br/>");
        printList(head);

        var x = 2;

        // delete all occurrences of 'x'
        head = deleteAllOccurOfX(head, x);
        document.write("<br/>Doubly linked list after deletion of " + x + " :<br/>");
        printList(head);

// This code contributed by gauravrajput1
</script>

Output

Original Doubly linked list:n2 2 10 8 4 2 5 2 
Doubly linked list after deletion of 2:n10 8 4 5 

Time Complexity: O(n)
Auxiliary Space: O(1) because no extra space is required 

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