算法第四版1.3背包、队列和栈：习题1.3.38

import edu.princeton.cs.algs4.StdOut;

public class GeneralizedQueue {
    public static void main(String[]args){
        GeneralizedQueue queue=new GeneralizedQueue<>();
        for (int i=1;i<10;i++)
            queue.insert(i);
        StdOut.println(queue.delete(9));
        StdOut.println(queue.delete(5));
        StdOut.println(queue.delete(1));
    }
    
    private Node first;
    private Node last;
    private int N;
    private class Node{
        Item item;
        Node next;
    }
    public GeneralizedQueue(){
        first=null;
        last=null;
        N=0;
    }
    public boolean isEmpty(){return first==null;}
    public void insert(Item x){
        Node newlast=new Node();
        newlast.item=x;
        if (isEmpty()){
            first=newlast;
            last=newlast;
        }
        else {
            last.next=newlast;
            last=newlast;
        }
        N++;
    }
    public Item delete(int k){
        if (k>N||k<1||first==null) return null;
        Item item;
        if (first==last){
            item=first.item;
            first=null;
            last=null;
        }
        else {
            Node current=first;
            if (k==1){
                item=first.item;
                first=first.next;
            }
            else {
                for (int i=1;i