編寫程式碼，移除未排序連結串列中的重複節點。

進階，

如果不得使用臨時緩衝區，該怎麼解決？

package test;

import java.util.HashSet;

public class RemoveDup {

	//利用HashSet
	public Node removeDup(Node head){
		if(head==null || head.next==null)
			return head;
		Node newHead = new Node(0);
		newHead.next = head;
		Node point = newHead;
		HashSet<Integer> set = new HashSet<Integer>();
		while(point.next != null){
			if(set.contains(point.next.val))
				point.next = point.next.next;
			else{
				set.add(point.next.val);
				point = point.next;
			}
		}
		return newHead.next;
	}
	
	//不利用臨時緩衝區
	public Node removeDup(Node head){
		if(head==null || head.next==null)
			return head;
		Node current = head;
		while(current != null){
			Node point = current;
			whille(point.next != null){
				if(point.next.val == current.val)
					point.next = point.next.next;
				else
					point = point.next;
			}
			current = current.next;
		}
		return head;
	}
	
}