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

29 Oct, 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++
Java
Python3
C#
Javascript
/* 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 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 listclass 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 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 functionsif __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# 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
<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 nodevar 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     */    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 listvar 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 review-team@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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