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

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