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Delete all occurrences of a given key in a doubly linked list
  • Difficulty Level : Easy
  • Last Updated : 23 May, 2021

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.
 



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 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 */
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 off 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 off 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 off 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 off 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 povar to the new node
        head = new_node;
 
        return head;
    }
 
    /*
     * Function to prvar 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:
2 2 10 8 4 2 5 2
Doubly linked list after deletion of 2:
10 8 4 5

Time Complexity: O(n)
This article is contributed by Ayush Jauhari. If you like GeeksforGeeks and would like to contribute, you can also write an article using write.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.
Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.
 

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