Delete a Doubly Linked List node at a given position

1

Given a doubly linked list and a position n. The task is to delete the node at the given position n from the beginning.

Initial doubly linked list

Doubly Linked List after deletion of node at position n = 2

Approach: Following are the steps:

  1. Get the pointer to the node at position n by traversing the doubly linked list up to the nth node from the beginning.
  2. Delete the node using the pointer obtained in Step 1. Refer this post.
/* C++ implementation to delete a doubly Linked List node 
   at the given position */
#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 the node at the given position
   in the doubly linked list */
void deleteNodeAtGivenPos(struct Node** head_ref, int n)
{
    /* if list in NULL or invalid position is given */
    if (*head_ref == NULL || n <= 0)
        return;

    struct Node* current = *head_ref;
    int i;

    /* traverse up to the node at position 'n' from
       the beginning */
    for (int i = 1; current != NULL && i < n; i++)
        current = current->next;

    /* if 'n' is greater than the number of nodes
       in the doubly linked list */
    if (current == NULL)
        return;

    /* delete the node pointed to by 'current' */
    deleteNode(head_ref, current);
}

/* 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)
{
    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 10<->8<->4<->2<->5 */
    push(&head, 5);
    push(&head, 2);
    push(&head, 4);
    push(&head, 8);
    push(&head, 10);

    cout << "Doubly linked list before deletion:n";
    printList(head);

    int n = 2;

    /* delete node at the given position 'n' */
    deleteNodeAtGivenPos(&head, n);

    cout << "\nDoubly linked list after deletion:n";
    printList(head);

    return 0;
}

Output:

Doubly linked list before deletion:
10 8 4 2 5
Doubly linked list after deletion:
10 4 2 5

Time Complexity: O(n), in worst case where n is the number of nodes in the doubly linked list.

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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