[CC150][2.1] 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?

LinkedList.java

import java.util.Random;

//* without temporary buffer
//* time O(N^2)

public class LinkedList<Item> {
	private class Node {
		Item item;
		Node next;
			
		public Node(Item item) {
			this.item = item;
			this.next = null;
		}
		
	}
		
	private Node first;
	private Node last;
	private int N;
	
	public LinkedList() {
		N = 0;
	}
	
	public boolean isEmpty() {
		return N == 0;
	}
	
	public void add(Item item) {
		if (isEmpty()) {
			first = new Node(item);
			last = first;
			N++;
		}
		else {
			Node oldLast = last;
			last = new Node(item);
			oldLast.next = last;
			N++;
		}
	}
	
	public void removeDuplicate() {
		Node curr = first;
		if (curr == null) return;	
		Node p, q;      // p points to previous Node of q
		while (curr != null) {
			p = curr;
			q = curr.next;
			while (q != null) {
				if (q.item.equals(curr.item)) {
					p.next = q.next;    // if q is same to current node, delete q, and q points to q.next
					q.item = null;
					q = q.next;
				}
				else {
					p = q;
					q = q.next;
				}
			}
			curr = curr.next;
		}
	}
	
	public String toString() {
		Node curr = first;
		String s = "";
		while (curr != null) {
			s += curr.item.toString() + " ";
			curr = curr.next;
		}
		s += "\n";
		return s;
	}
	
	
	public static void main (String[] args) {
		LinkedList<Integer> test = new LinkedList<Integer>();
		Random rd = new Random();
		for (int i = 0; i < 10; i++) {
			test.add(rd.nextInt(10));
		}
		System.out.println(test.toString());
		test.removeDuplicate();
		System.out.println(test.toString());
	}
}