//a simpler linked list implementation without parametric polymorphism and Iterator
//Author: Konstantin Voevodski
//Date: 6/4/07

public class mySimpleLinkedList
{
    private static class Node
    {
        public int data;
        public Node prev;
        public Node next;
        
        public Node(int d, Node p, Node n)
        {
            data = d;
            prev = p;
            next = n;
        }
    }
    
    private int size;
    private int modCount = 0;
    private Node beginMarker;
    private Node endMarker;
    
    public mySimpleLinkedList()
    {
        clear();
    }
    
    public void clear()
    {
        beginMarker = new Node(-1,null,null);
        endMarker = new Node(-1,beginMarker,null);
        //it is irrelevant what is stored in the data field of beginMarker and endMarker
        beginMarker.next = endMarker;
        size = 0;
        modCount++;
    }
    
    public int size()
    {
        return size;
    }
    
    public boolean isEmpty()
    {
        return(size == 0);
    }
    
    private void addBefore(Node p, int x)
    //add new node before p, conceptually modifying four links
    {
        Node newNode = new Node(x,p.prev,p);
        newNode.prev.next = newNode;
        p.prev = newNode;
        size++;
        modCount++;
    }
    
    private int remove(Node p)
    //remove node p, conceptually modifying two links
    {
        p.next.prev = p.prev;
        p.prev.next = p.next;
        size--;
        modCount++;
        return p.data;
    }
    
    private Node getNode(int idx)
    //return a Node at the given index
    {
        if(idx < 0 || idx > size())
        {
            throw new IndexOutOfBoundsException();
        }
        Node p;
        if(idx < size()/2)
        //traverse list from the front
        {
            p = beginMarker.next;
            for(int i = 0; i < idx; i++)
            {
                p = p.next;
            }
        }
        else
        //traverse list from the back
        {
            p = endMarker;
            for(int i = size(); i > idx; i--)
            {
                p = p.prev;
            }
        }
        return p;
    }
    
    public boolean add(int x)
    {
        add(size(),x);
        return true;
    }
    
    public void add(int index, int x)
    {
        addBefore(getNode(index),x);
    }
    
    public int get(int index)
    {
        return (getNode(index).data);
    }
    
    public int set(int index, int newVal)
    {
        Node p = getNode(index);
        int oldVal = p.data;
        p.data = newVal;
        return oldVal;
    }
    
    public int remove(int index)
    {
        return(remove(getNode(index)));
    }
}