Remove duplicates from an unsorted doubly linked list | Java mplementation to remove duplicates from an unsorted doubly linked list ; a node of the doubly linked list ; Function to delete a node in a Doubly Linked List . head_ref -- > pointer to head node pointer . del -- > pointer to node to be deleted . ; base case ; If node to be deleted is head node ; Change next only if node to be deleted is NOT the last node ; Change prev only if node to be deleted is NOT the first node ; function to remove duplicates from an unsorted doubly linked list ; if doubly linked list is empty ; unordered_set ' us ' implemented as hash table ; traverse up to the end of the list ; if current data is seen before ; store pointer to the node next to ' current ' node ; delete the node pointed to by ' current ' ; update ' current ' ; insert the current data in ' us ' ; move to the next node ; Function to insert a node at the beginning of the Doubly Linked List ; allocate node ; put in the data ; since we are adding at the beginning , prev is always null ; link the old list off the new node ; change prev of head node to new node ; move the head to point to the new node ; Function to print nodes in a given doubly linked list ; if list is empty ; Driver Code ; Create the doubly linked list : 8 < -> 4 < -> 4 < -> 6 < -> 4 < -> 8 < -> 4 < -> 10 < -> 12 < -> 12 ; remove duplicate nodes
import java . util . * ; class GFG { static class Node { int data ; Node next ; Node prev ; } ; static Node deleteNode ( Node head_ref , Node del ) { if ( head_ref == null del == null ) return null ; if ( head_ref == del ) head_ref = del . next ; if ( del . next != null ) del . next . prev = del . prev ; if ( del . prev != null ) del . prev . next = del . next ; return head_ref ; } static Node removeDuplicates ( Node head_ref ) { if ( ( head_ref ) == null ) return null ; HashSet < Integer > us = new HashSet < > ( ) ; Node current = head_ref , next ; while ( current != null ) { if ( us . contains ( current . data ) ) { next = current . next ; head_ref = deleteNode ( head_ref , current ) ; current = next ; } else { us . add ( current . data ) ; current = current . next ; } } return head_ref ; } static Node push ( Node head_ref , int new_data ) { Node new_node = new Node ( ) ; new_node . data = new_data ; new_node . prev = null ; new_node . next = ( head_ref ) ; if ( ( head_ref ) != null ) ( head_ref ) . prev = new_node ; ( head_ref ) = new_node ; return head_ref ; } static void printList ( Node head ) { if ( head == null ) System . out . print ( " Doubly ▁ Linked ▁ list ▁ empty " ) ; while ( head != null ) { System . out . print ( head . data + " ▁ " ) ; head = head . next ; } } public static void main ( String [ ] args ) { Node head = null ; head = push ( head , 12 ) ; head = push ( head , 12 ) ; head = push ( head , 10 ) ; head = push ( head , 4 ) ; head = push ( head , 8 ) ; head = push ( head , 4 ) ; head = push ( head , 6 ) ; head = push ( head , 4 ) ; head = push ( head , 4 ) ; head = push ( head , 8 ) ; System . out . println ( " Original ▁ Doubly ▁ linked ▁ list : " ) ; printList ( head ) ; head = removeDuplicates ( head ) ; System . out . println ( " Doubly linked list after " ▁ + ▁ " removing duplicates : "); printList ( head ) ; } }