1.3.36随机迭代器。为上一题中的RandomQueue<Item>编写一个迭代器，随机返回队列中的所有元素。

答：

import java.util.Iterator;

public class RandomQueue<Item> implements Iterable<Item>

{

    private int N=0;

    private Item[] a=(Item[]) new Object[1];

    public RandomQueue()

    {

    }

   

    public boolean isEmpty()

    {return N==0;}

   

    public void enqueue(Item item)

    {

        if(N==a.length) resize(2*N);

        a[N]=item;

        N++;

    }

   

    public Item dequeue()

    {

        int r=StdRandom.uniform(N);

        Item item=a[r];

        a[r]=a[N-1];

        N--;

        if(N==a.length/4) resize(2*N);

        return item;

     }

   

    public Item sample()

    {

        int r=StdRandom.uniform(N);

        return a[r];

    }

   

    private void resize(int max)

    {

        Item[] temp=(Item[]) new Object[max];

        for(int i=0;i<N;i++)

            temp[i]=a[i];

        a=temp;

    }

   

    public Iterator<Item> iterator()  {return new ListIterator();}

   

    private class ListIterator implements Iterator<Item>

    {

        private int index=0;

        public ListIterator()

        {

            for (int i = 0; i < N; i++)

            {

               int r = i + StdRandom.uniform(N-i);     // between i and n-1

               Item temp = a[i];

               a[i] = a[r];

               a[r] = temp;

            }

        }

        public boolean hasNext(){return index!=N;}

        public void remove(){}

        public Item next()

        {

           

            Item item=a[index];

            index++;

            return item;

        }//end next

      }//end class ListIterator

    public static void main(String[] args)

    {

        RandomQueue<Card> cards=new RandomQueue<Card>();

       

        for(int value=1;value<=13;value++)

            for(int type=1;type<=4;type++)

               {

                  Card c=new Card();

                  c.value=value;

                  c.type=type;

                  cards.enqueue(c);

              }//end for

     

      while(!cards.isEmpty())

      {

           Card c=cards.dequeue();

           StdOut.print("("+c.value+"," +c.type+")");

      }//end while

   }//end main

}//end class