public class LinkedList implements List {
	
	protected static class ListNode implements List.Node {
		  public int data;     
		  public ListNode next; 
		  public int getData() { return data; }
		  ListNode() {
			  data = 0;
		  }
		  ListNode (int x) {
			  data = x;
		  }
		}
	
	int length = 0;
	ListNode head = new ListNode();
	ListNode tail = new ListNode();
	
	LinkedList() {
		head.next = tail;
		tail.next = null;
	}

	public void add(int a) {
		ListNode ln = new ListNode(a);
		ln.next = head.next;
		head.next = ln;
		length ++;
	}

	public Node find(int a) {
		ListNode aktuell = head;
		while (aktuell.next != null) {
			if (a == aktuell.data) return aktuell;
			else aktuell = aktuell.next;
		}
		return null;
	}

	public Node getFirst() {
		return head.next;
	}

	public Node getLast() {
		ListNode aktuell = head;
		while (aktuell != null) {
			if (aktuell.next == null) return aktuell;
			else aktuell = aktuell.next;
		}
		return null;
	}

	public Node getNext(Node e) {
		
		return getListNode(e).next;
	}

	public Node getPrevious(Node e) {
		ListNode aktuell = head;
		while (aktuell != null) {
			if (aktuell.next == e) return aktuell;
			else aktuell = aktuell.next;
		}
		return null;
	}

	public void insert(Node n, int a) {
		ListNode neu = new ListNode(a);
		ListNode ln = getListNode(n);
		neu.next = ln.next;
		ln.next = neu;
		length ++;
		
	}

	public void remove(int a) {
		Node n = find(a);
		remove(n);
		
	}

	public void remove(Node e) {
		ListNode weg = getListNode(e);
		
		Node n = getPrevious(e);
		ListNode davor = getListNode(n);
		
		davor.next = weg.next;
		length --;
	}

	public int size() {
		return length;
	}
	
	public ListNode getListNode (Node a) {
		ListNode aktuell = head;
		while (aktuell.next != null) {
			if (aktuell.equals(a) == true) return aktuell;
			else aktuell = aktuell.next;
		}
		return null;
	}

}