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 Initializecurrent= head_ref Declarenextwhile current != NULL if current->data == x next = current->nextdeleteNode(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++ 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 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 << "\nDoubly linked list after deletion of " << x << ":n"; printList(head); 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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