CC2.1 - Write code to remove duplicates from an unsorted linked list. FOLLOW UP How would you solve this problem if a temporary buffer is not allowed?

CC2.1

import java.util.Hashtable;

public class removeDuplicates {
	public static void Solution(LinkedListNode head) {
		if (head == null) return;
		Hashtable<Integer, Boolean> table = new Hashtable<Integer, Boolean>();
		LinkedListNode dummyHead = new LinkedListNode(0);
		dummyHead.next = head;
		LinkedListNode ptr = dummyHead;
		while(ptr.next != null) {
			if(!table.containsKey(ptr.next.val)) {
				table.put(ptr.next.val, true);
				ptr = ptr.next;
			} else {
				 ptr.next = ptr.next.next;
			}
		}	
	}
	
	public static void main(String[] args) {
		LinkedListNode a = new LinkedListNode(3);
		LinkedListNode b = new LinkedListNode(1);
		LinkedListNode c = new LinkedListNode(1);
		LinkedListNode d = new LinkedListNode(18);
		LinkedListNode e = new LinkedListNode(1);
		a.next = b;
		b.next = c;
		c.next = d;
		d.next = e;
		a.printList();
		removeDuplicates.Solution(a);
		System.out.println();
		a.printList();
		
	}

}