Java Program For Removing Duplicates From An Unsorted Linked List

// Java program to remove duplicates from unsorted
// linked list

class LinkedList {

    static Node head;

    static class Node {

        int data;
        Node next;

        Node(int d)
        {
            data = d;
            next = null;
        }
    }

    /* Function to remove duplicates from an
       unsorted linked list */
    void remove_duplicates()
    {
        Node ptr1 = null, ptr2 = null, dup = null;
        ptr1 = head;

        /* Pick elements one by one */
        while (ptr1 != null && ptr1.next != null) {
            ptr2 = ptr1;

            /* Compare the picked element with rest
                of the elements */
            while (ptr2.next != null) {

                /* If duplicate then delete it */
                if (ptr1.data == ptr2.next.data) {

                    /* sequence of steps is important here
                     */
                    ptr2.next = ptr2.next.next;
                    System.gc();
                }
                else /* This is tricky */ {
                    ptr2 = ptr2.next;
                }
            }
            ptr1 = ptr1.next;
        }
    }

    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();
        list.head = new Node(10);
        list.head.next = new Node(12);
        list.head.next.next = new Node(11);
        list.head.next.next.next = new Node(11);
        list.head.next.next.next.next = new Node(12);
        list.head.next.next.next.next.next = new Node(11);
        list.head.next.next.next.next.next.next
            = new Node(10);

        System.out.println(
            "Linked List before removing duplicates : ");
        list.printList(head);

        list.remove_duplicates();
        System.out.println("\n");
        System.out.println(
            "Linked List after removing duplicates : ");
        list.printList(head);
    }
}
// This code has been contributed by Mayank Jaiswal

import java.io.*;

// structure of a node in the linked list
class Node {
    int data;
    Node next;

    Node(int d)
    {
        data = d;
        next = null;
    }
}

// class for the linked list
class LinkedList {
    Node head;

    // function to insert a node in the linked list
    public void push(int new_data)
    {
        Node new_node = new Node(new_data);
        new_node.next = head;
        head = new_node;
    }

    // function to sort the linked list
    public void sortList()
    {
        // pointer to traverse the linked list
        Node current = head;
        Node index = null;

        // loop to traverse the linked list
        while (current != null) {
            // loop to compare current node with all other
            // nodes
            index = current.next;
            while (index != null) {
                // checking for duplicate values
                if (current.data == index.data) {
                    // deleting the duplicate node
                    current.next = index.next;
                    index = current.next;
                }
                else {
                    index = index.next;
                }
            }
            current = current.next;
        }
    }

    // function to display the linked list
    public void printList()
    {
        Node node = head;
        while (node != null) {
            System.out.print(node.data + " ");
            node = node.next;
        }
        System.out.println();
    }
}

// main class
class Main {
    public static void main(String[] args)
    {
        LinkedList ll = new LinkedList();
        ll.push(20);
        ll.push(13);
        ll.push(13);
        ll.push(11);
        ll.push(11);
        ll.push(11);

        System.out.println(
            "Linked List before removing duplicates : ");
        ll.printList();

        ll.sortList();

        System.out.println(
            "Linked List after removing duplicates : ");
        ll.printList();
    }
}

// Java program to remove duplicates
// from unsorted linkedlist

import java.util.HashSet;

public class removeDuplicates {
    static class node {
        int val;
        node next;

        public node(int val) { this.val = val; }
    }

    /* Function to remove duplicates from a
       unsorted linked list */
    static void removeDuplicate(node head)
    {
        // Hash to store seen values
        HashSet<Integer> hs = new HashSet<>();

        /* Pick elements one by one */
        node current = head;
        node prev = null;
        while (current != null) {
            int curval = current.val;

            // If current value is seen before
            if (hs.contains(curval)) {
                prev.next = current.next;
            }
            else {
                hs.add(curval);
                prev = current;
            }
            current = current.next;
        }
    }

    /* Function to print nodes in a given linked list */
    static void printList(node head)
    {
        while (head != null) {
            System.out.print(head.val + " ");
            head = head.next;
        }
    }

    public static void main(String[] args)
    {
        /* The constructed linked list is:
         10->12->11->11->12->11->10*/
        node start = new node(10);
        start.next = new node(12);
        start.next.next = new node(11);
        start.next.next.next = new node(11);
        start.next.next.next.next = new node(12);
        start.next.next.next.next.next = new node(11);
        start.next.next.next.next.next.next = new node(10);

        System.out.println(
            "Linked list before removing duplicates :");
        printList(start);

        removeDuplicate(start);

        System.out.println(
            "\nLinked list after removing duplicates :");
        printList(start);
    }
}

// This code is contributed by Rishabh Mahrsee