/**
 * 雙端連結串列
 */
class MyLinkList {
    public Link first;
    public Link last;
    public MyLinkList(){
        first = null;
        last = null;
    }
    //判空
    public boolean isEmpty(){
        return first == null;
    }
    //從頭插入
    public void insertFirst(int dd){
        Link link = new
 
 Link(dd);
        if(isEmpty()) {
            last = link;
        }
        link.next = first;
        first = link;
    }
    //從尾部插入
    public void insertLast(int dd){
        Link link = new Link(dd);
        if(isEmpty()){
            first = link;
        }else {
            last.next = link;
        }
 

        last = link;
    }
    //從開始位置刪除
    public int deleteFirst(){
        int temp = first.dData;
        if(first.next == null){
            last = null;
        }
        first = first.next;
        return temp;
    }
    //列印
    public void displayList(){
        System.out.println("List(first -> last):"
 
);
        Link current = first;
        while (current != null){
            current.displayLink();
            current = current.next;
        }
        System.out.println();
    }
    public static void main(String[] args){
        MyLinkList myLinkList = new MyLinkList();
        myLinkList.insertFirst(22);
        myLinkList.insertFirst(44);
        myLinkList.insertFirst(66);
        myLinkList.insertLast(11);
        myLinkList.insertLast(33);
        myLinkList.insertLast(55);
        myLinkList.displayList();

        myLinkList.deleteFirst();
        myLinkList.deleteFirst();
        myLinkList.displayList();
    }
}

class Link{
    public int dData;   //資料
    public Link next;   //下一個節點的引用
    public Link(int d){
        dData = d;
    }
    public void displayLink(){
        System.out.print(dData + " ");
    }
}