# 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: ## Recommended: Please try your approach on {IDE} first, before moving on to the solution.

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 ` ` `  `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 begining, ` `    ``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 << ````" Doubly 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(````" Doubly linked list after deletion of"``` `+ x +``":"``); ` `        ``printList(head); ` `    ``} ` `} ` ` `  `// This code is contributed by rachana soma `

## 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(````" Doubly linked list after deletion of"``` `+ x +``":"``);  ` `        ``printList(head);  ` `    ``}  ` `}  ` ` `  `// This code is contributed by Arnab Kundu `

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)

Please write comments if you find anything incorrect, or you want to share more information about the topic discussed above.

This article is attributed to GeeksforGeeks.org

## tags:

Linked List doubly linked list Linked List

code

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