# 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
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++ 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)

/* 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' */

/* 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 */

/* change prev of head node to new node */
if ((*head_ref) != NULL)

/* move the head to point to the new node */
}

/* Function to print nodes in a given doubly
void printList(struct Node* head)
{
/* if list is empty */
if (head == NULL)
cout << "Doubly Linked list empty";

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

/* 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 */

cout << "Original Doubly linked list:n";

int x = 2;

/* delete all occurrences of 'x' */

cout << "\nDoubly linked list after deletion of "
<< x << ":n";

return 0;
}
```

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 contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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