Algs4-1.4.31三个栈实现的双向队列

1.4.31三个栈实现的双向队列。使用三个栈实现一个双向队列，使得双向队列的每个操作所需的栈操作均摊后为一个常数。
答：

public class E1d4d31<Item>
{
    Stack<Item> sLeft=new Stack<Item>();
    Stack<Item> sRight=new Stack<Item>();
    Stack<Item> sTemp=new Stack<Item>();
    boolean TempIsRight=false;//false表示中转栈存的是左栈数据，true表示中转栈存右栈数据。
    //
    public boolean isEmpty()
    {
        return sLeft.isEmpty() && sRight.isEmpty()&&sTemp.isEmpty();
    }
   
    public int size()
    {
        return sLeft.size()+sRight.size()+sTemp.size();
    }
   
    public void pushLeft(Item item)
    {
        sLeft.push(item);
    }
   
    public Item popLeft()
    {
        if(!sLeft.isEmpty())
            return sLeft.pop();//左栈有内容时直接弹出
        else if(!sTemp.isEmpty() && TempIsRight)//左栈无内容，中转栈有内容，中转栈是右栈内容时，从中转栈中弹出
            return sTemp.pop();
        else if(!sTemp.isEmpty() && !TempIsRight)//左栈无内容，中转栈有内容，中转栈是左栈内容时，把中转栈内容全部倒入左栈，然后从左栈弹出
        {
            while(!sTemp.isEmpty())
                 sLeft.push(sTemp.pop());
           return sLeft.pop();
        }
        else if(sTemp.isEmpty() && !sRight.isEmpty())//左栈无内容，中转栈无内容，右栈有内容，把右栈内容全部倒入中转栈，中转栈存入内容标记为右栈，然后从中转栈弹出。
        {
            while(!sRight.isEmpty())
                sTemp.push(sRight.pop());
            TempIsRight=true;
            return sTemp.pop();
        }
        else//左栈无内容，中转栈无内容，右栈无内容时，弹出null
        {
            return null;
        }
   }
   
    public void pushRight(Item item)
    {
        sRight.push(item);
    }
   
    public Item popRight()//与popLeft原理相同
    {
        if(!sRight.isEmpty())
            return sRight.pop();
        else if(!sTemp.isEmpty() && !TempIsRight)
            return sTemp.pop();
        else if(!sTemp.isEmpty() && TempIsRight)
        {
            while(!sTemp.isEmpty())
                 sRight.push(sTemp.pop());
           return sRight.pop();
        }
        else if(sTemp.isEmpty() && !sLeft.isEmpty())
        {
            while(!sLeft.isEmpty())
                sTemp.push(sLeft.pop());
            TempIsRight=false;
            return sTemp.pop();
        }
        else
        {
            return null;
        }
    }
   
   
    public static void main(String[] args)
    {
        E1d4d31<String> d=new E1d4d31<String>();
        d.pushLeft("1");
        d.pushRight("2");
        StdOut.printf("Deque size is:%d\n",d.size());
        StdOut.printf("popLeft is:%s\n",d.popLeft());
        StdOut.printf("popLeft is:%s\n",d.popLeft());
        //
        d.pushLeft("1");
        d.pushRight("2");
        StdOut.println("-------");
        StdOut.printf("Deque size is:%d\n",d.size());
        StdOut.printf("popRight is %s\n",d.popRight());
        StdOut.printf("popRight is %s\n",d.popRight());
        //
        d.pushLeft("1");
        d.pushRight("2");
        d.pushRight("3");
        StdOut.println("-------");
        StdOut.printf("popLeft is:%s\n",d.popLeft());
        StdOut.printf("popLeft is:%s\n",d.popLeft());
        d.pushRight("4");
        StdOut.printf("popRight is %s\n",d.popRight());
        StdOut.printf("popRight is %s\n",d.popRight());
         StdOut.printf("popRight is %s\n",d.popRight());
    }
}