Career Cup 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?

C2P1.java

package chapter2;

import java.util.HashSet;

/*
 * Career Cup 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?
 */
public class C2P1 {

  /*
	 * use a hash set to record existing value along with traversing the linked list
	 * time complexity: O(n)
	 * space complexity: O(n)
	 */
	public static void removeDuplicatesUsingBuffer(Node header){
		HashSet<Integer> hashSet = new HashSet<Integer>();
		Node prev = null;
		while(header != null){
			if(hashSet.contains(header.value))
				prev.next = header.next;
			else {
				prev = header;
				hashSet.add(header.value);
			}
			header = header.next;
		}
	}
	/*
	 * traverse the linked list with a inner loop checking equality
	 * time complexity: O(n^2)
	 * space complexity: O(1)
	 */
	public static void removeDuplicatesNotUsingBuffer(Node header) {
		Node prev, post;
		while(header != null){
			prev = header;
			post = header.next;
			while(post != null){
				if(post.value == header.value){
					prev.next = post.next;
				}
				else {
					prev = post;
				}
				post = post.next;
			}
			header = header.next;
		}
		
	}
	
	public static void main(String[] args) {
		int[] array = {1,2,2,3,1,5,4,5};
		Node header = new Node(array);
		Node header1 = new Node(array);
		header.printLinkList();
		removeDuplicatesUsingBuffer(header);
		header.printLinkList();
		removeDuplicatesNotUsingBuffer(header1);
		header1.printLinkList();
	}

}

Node.java

package chapter2;

public class Node {

  public int value;
	public Node next;

	public Node(int value) {
		this.value = value;
		this.next = null;
	}
	
	public Node(int[] array){
		if (array.length != 0) {
			this.value = array[0];
			this.next = null;
		}
		for (int i = 1; i < array.length; i++) {
			this.appendToTail(array[i]);
		}
	}
	
	
	public void  printLinkList(){
		Node pointer = this;
		while (pointer != null) {
			System.out.printf("%d%s",pointer.value, pointer.next != null ? " -> ":"\n");
			pointer = pointer.next;
		}
	}

	public void appendToTail(int d) {
		Node pointer = this;
		Node node = new Node(d);
		while(pointer.next != null){
			pointer = pointer.next;
		}
		pointer.next = node;
	}
	
	@Override
	public String toString(){
		return String.format("value of node:%d", value);
	}
	
}