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public class Deque<Item> implements Iterable<Item> {

    private int size; // number of items
    private Node first; // top of stack
    private Node last;

    private class Node {

        Item item;
        Node next;
        Node previous;

        public Node(Item itemX) {
            item = itemX;
        }

        public Node() {
        }
    }

    public Deque() {
        first = null;
        last = null;
        size = 0;
    }

    public boolean isEmpty() {
        return first == null;
    }

    public int size() {
        return size;
    }

    public void pushRight(Item item) {
        //adds item to top of stack
        Node newNode = new Node(item);
        newNode.next = null;
        if (isEmpty()) {
            first = newNode;
        } else {
            last.next = newNode;
            newNode.previous = last;
        }
        last = newNode;

    }
public void changeLeft(int k, Item newItem){
        int i = 1;
        Node current = first;

        while(i < k && current != null){
            current = current.next;
            i++;
        }
        if(current != null){
            current.item = newItem;
        }
        else{
            System.out.println("Linkedlist out of bounds");
        }

    }

    public void changeRight(int k, Item newItem){
        int size2 = size;
        Node current = last;

        while(size2 > k && current != null){
            current = current.previous;
            size--;
        }
        if(current != null){
            current.item = newItem;
        }
        else{
            System.out.println("Linkedlist out of bounds");
        }
    }




    public void pushLeft(Item item) {
        //adds item to bottom of stack

        Node newNode = new Node(item);

        if (isEmpty()) {
            last = newNode;
        } else {
            first.previous = newNode;
        }
        newNode.next = first;
        first = newNode;

    }

    public Item popLeft() {
        Item t = first.item;
        if (first.next == null) {
            last = null;
        } else {
            first.next.previous = null;
        }
        first = first.next;
        return t;
    }

    public Item popRight() {
        Item t = last.item;
        if (first.next == null) {
            first = null;
        } else {
            last.previous.next = null;
        }
        last = last.previous;
        return t;
    }

    public void printDeque() {
        Node tmpNode = first;

        while (tmpNode != null) {
            System.out.print(tmpNode.item + " -> ");
            tmpNode = tmpNode.next;
        }

        System.out.print("null");
    }

    @Override
    public Iterator<Item> iterator() {
        throw new UnsupportedOperationException("Not supported yet."); //To change body of generated methods, choose Tools | Templates.