Doubly Link List Set 1| Introduction and Insertion

Write a function to delete a given node in a doubly linked list.

(a) Original Doubly Linked List

(a) After deletion of head node

(a) After deletion of middle node

(a) After deletion of last node

Algorithm

Let the node to be deleted is *del*.

1) If node to be deleted is head node, then change the head pointer to next current head.

2) Set *next *of previous to *del*, if previous to *del* exixts.

3) Set *prev *of next to *del*, if next to *del* exixts.

## C

#include <stdio.h> #include <stdlib.h> /* 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); return; } /* UTILITY FUNCTIONS */ /* 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 This function is same as printList() of singly linked lsit */ void printList(struct node *node) { while(node!=NULL) { printf("%d ", node->data); node = node->next; } } /* Drier program to test above functions*/ int main() { /* Start with the empty list */ struct 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); printf("\n Original Linked list "); printList(head); /* delete nodes from the doubly linked list */ deleteNode(&head, head); /*delete first node*/ deleteNode(&head, head->next); /*delete middle node*/ deleteNode(&head, head->next); /*delete last node*/ /* Modified linked list will be NULL<-8->NULL */ printf("\n Modified Linked list "); printList(head); getchar(); }

## Java

// Java program to delete a node from doubly linked list class LinkedList { static Node head = null; class Node { int data; Node next, prev; Node(int d) { data = d; next = prev = null; } } /*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 == null || del == null) { return; } /* If node to be deleted is head node */ if (head == del) { head = 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*/ 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(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); /* change prev of head node to new node */ if ((head) != null) { (head).prev = new_node; } /* move the head to point to the new node */ (head) = new_node; } /*Function to print nodes in a given doubly linked list This function is same as printList() of singly linked lsit */ void printList(Node node) { while (node != null) { System.out.print(node.data + " "); node = node.next; } } public static void main(String[] args) { LinkedList list = new LinkedList(); /* Let us create the doubly linked list 10<->8<->4<->2 */ list.push(head, 2); list.push(head, 4); list.push(head, 8); list.push(head, 10); System.out.println("Original Linked list "); list.printList(head); /* delete nodes from the doubly linked list */ list.deleteNode(head, head); /*delete first node*/ list.deleteNode(head, head.next); /*delete middle node*/ list.deleteNode(head, head.next); /*delete last node*/ System.out.println(""); /* Modified linked list will be NULL<-8->NULL */ System.out.println("Modified Linked List"); list.printList(head); } } // This code has been contributed by Mayank Jaiswal

## Python

# Program to delete a node in doubly linked list # for Garbage collection import gc # A node of the doublly linked list class Node: # Constructor to create a new node def __init__(self, data): self.data = data self.next = None self.prev = None class DoublyLinkedList: # Constructor for empty Doubly Linked List def __init__(self): self.head = None # Function to delete a node in a Doubly Linked List. # head_ref --> pointer to head node pointer. # dele --> pointer to node to be deleted def deleteNode(self, dele): # Base Case if self.head is None or dele is None: return # If node to be deleted is head node if self.head == dele: self.head = dele.next # Change next only if node to be deleted is NOT # the last node if dele.next is not None: dele.next.prev = dele.prev # Change prev only if node to be deleted is NOT # the first node if dele.prev is not None: dele.prev.next = dele.next # Finally, free the memory occupied by dele # Call python garbage collector gc.collect() # Given a reference to the head of a list and an # integer,inserts a new node on the front of list def push(self, new_data): # 1. Allocates node # 2. Put the data in it new_node = Node(new_data) # 3. Make next of new node as head and # previous as None (already None) new_node.next = self.head # 4. change prev of head node to new_node if self.head is not None: self.head.prev = new_node # 5. move the head to point to the new node self.head = new_node def printList(self, node): while(node is not None): print node.data, node = node.next # Driver program to test the above functions # Start with empty list dll = DoublyLinkedList() # Let us create the doubly linked list 10<->8<->4<->2 dll.push(2); dll.push(4); dll.push(8); dll.push(10); print "\n Original Linked List", dll.printList(dll.head) # delete nodes from doubly linked list dll.deleteNode(dll.head) dll.deleteNode(dll.head.next) dll.deleteNode(dll.head.next) # Modified linked list will be NULL<-8->NULL print "\n Modified Linked List", dll.printList(dll.head) # This code is contributed by Nikhil Kumar Singh(nickzuck_007)

Time Complexity: O(1)

Time Complexity: O(1)

Please write comments if you find any of the above codes/algorithms incorrect, or find better ways to solve the same problem.