public class Lz {
    private Node first;
    private Node last;
    private int size;

    public Lz() {
        first = null;
        last = null;
        size = 0;

    }

    public void push(int item) {//往队列中添加元素
        Node newNode;
        if (size == 0) {
            newNode = new Node(null, null, item);
            first = newNode;
        } else {
            newNode = new Node(last, null, item);
            last.next = newNode;
        }
        last = newNode;
        size++;
    }

    public int pop() throws Exception {//队列第一个元素出列
        if (size == 0) {
            throw new Exception("QueueEmpty");
        } else {
            int res = first.item;
            if (size == 1) {
                first = null;
                last = null;
            } else {
                first = first.next;
                first.perv = null;
            }
            size--;
            return res;
        }
    }

    public int peek() {
        return first.item;
    }

    private Node jump(int position) throws Exception {//通过用户给予的位置信息，移动至指定位置
        if (position > 0 && position <= size) {
            Node nowNode = first;
            while (position - 1 != 0) {
                nowNode = nowNode.next;
                position--;
            }
            return nowNode;
        } else {
            System.out.println("error...");
            throw new Exception("error...");
        }
    }


private static class Node {
    private Node perv;
    private Node next;
    private final int item;

    public Node(Node perv, Node next, int item) {
        this.perv = perv;
        this.next = next;
        this.item = item;
    }
}

}