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C++ Program For Deleting A Node In A Doubly Linked List

  • Last Updated : 15 Dec, 2021

Pre-requisite: Doubly Link List Set 1| Introduction and Insertion

Write a function to delete a given node in a doubly-linked list. 
Original Doubly Linked List 

Approach: The deletion of a node in a doubly-linked list can be divided into three main categories: 

  • After the deletion of the head node. 

  • After the deletion of the middle node. 

  • After the deletion of the last node.

All three mentioned cases can be handled in two steps if the pointer of the node to be deleted and the head pointer is known. 

  1. If the node to be deleted is the head node then make the next node as head.
  2. If a node is deleted, connect the next and previous node of the deleted node.

Algorithm 

  • Let the node to be deleted be del.
  • If node to be deleted is head node, then change the head pointer to next current head.
if headnode == del then
      headnode =  del.nextNode
  • Set next of previous to del, if previous to del exists.
if del.nextNode != none 
      del.nextNode.previousNode = del.previousNode 
  • Set prev of next to del, if next to del exists.
if del.previousNode != none 
      del.previousNode.nextNode = del.next

C++




// C++ program to delete a node from
// Doubly Linked List
#include <bits/stdc++.h>
using namespace std;
  
// Anode of the doubly linked list
class Node 
    public:
    int data; 
    Node* next; 
    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(Node** head_ref, 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); 
    return
  
// UTILITY FUNCTIONS 
/* Function to insert a node at the
   beginning of the Doubly Linked List */
void push(Node** head_ref, 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_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. This function is 
   same as printList() of singly linked list */
void printList(Node* node) 
    while (node != NULL) 
    
        cout << node->data << " "
        node = node->next; 
    
  
// Driver code
int main() 
    // Start with the empty list 
    Node* head = NULL; 
  
    /* Let us create the doubly linked list 
       10<->8<->4<->2 */
    push(&head, 2); 
    push(&head, 4); 
    push(&head, 8); 
    push(&head, 10); 
  
    cout << "Original Linked list "
    printList(head); 
  
    /* Delete nodes from the doubly 
       linked list */
    // Delete first node
    deleteNode(&head, head); 
  
    // Delete middle node
    deleteNode(&head, head->next); 
  
    // Delete last node
    deleteNode(&head, head->next); 
  
    /* Modified linked list will be 
       NULL<-8->NULL */
    cout << "Modified Linked list "
    printList(head); 
  
    return 0;
// This code is contributed by rathbhupendra

Output:

Original Linked list 10 8 4 2 
Modified Linked list 8

Complexity Analysis: 

  • Time Complexity: O(1). 
    Since traversal of the linked list is not required so the time complexity is constant.
  • Space Complexity: O(1). 
    As no extra space is required, so the space complexity is constant.

Please refer complete article on Delete a node in a Doubly Linked List for more details!


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