Remove duplicates from an unsorted linked list

Question

import java.util.*;
/*
 *  Remove duplicates from an unsorted linked list
 */
public class LinkedListNode {  
    public int data;  
    public LinkedListNode next;          


        

Answer 1

You can use the following java method to remove duplicates:

1) With complexity of O(n^2)

public void removeDuplicate(Node head) {
    Node temp = head;
    Node duplicate = null;                //will point to duplicate node
    Node prev = null;                     //prev node to duplicate node
    while (temp != null) {                //iterate through all nodes       
        Node curr = temp;
        while (curr != null) {                     //compare each one by one
            /*in case of duplicate skip the node by using prev node*/
            if (curr.getData() == temp.getData() && temp != curr) {        
                duplicate = curr;
                prev.setNext(duplicate.getNext());
            }
            prev = curr;
            curr = curr.getNext();
        }
        temp = temp.getNext();
    }
}

Input:1=>2=>3=>5=>5=>1=>3=>

Output:1=>2=>3=>5=>

2)With complexity of O(n) using hash table.

public void removeDuplicateUsingMap(Node head) {
    Node temp = head;
    Map hash_map = new HashMap(); //create a hash map
    while (temp != null) {  
        if (hash_map.get(temp.getData()) == null) {  //if key is not set then set is false
            hash_map.put(temp.getData(), false);
        } else {                                   //if key is already there,then delete the node
            deleteNode(temp,head);
        }
        temp = temp.getNext();
    }

}

public void deleteNode(Node n, Node start) {
        Node temp = start;
        if (n == start) {
            start = null;
        } else {
            while (temp.getNext() != n) {
                temp = temp.getNext();
            }

            temp.setNext(n.getNext());

        }
    }

Input:1=>2=>3=>5=>5=>1=>3=>

Output:1=>2=>3=>5=>