question:

Delete kth element. Implement a class that supports the following API:

public clas GeneralizedQueue<Item>
            GeneralizedQueue() //create an empty queue
    boolean isEmpty()          //is the queue empty?
       void insert(Item x)     //add an item
       Item delete(int k)      //delete and return the kth least recently inserted item 

First, develop an implementation that an array implementation, and then develop one that uses a linked-list implementation. Note: the algorithms and data structures that we introduce in CHAPTER 3 make it possible to develop an implementation that can guarantee that both insert() and delete() take time prortional to the logarithm of number of items in the queue----see EXERCISE 3.5.27.

answer:

//题目要求是要用数组可链表分别实现，我这就只用链表实现了一下

import edu.princeton.cs.algs4.*;

public class GeneralizedQueue<Item>
{
    private class Node
    {
        Item item;
        Node next;
    }
    
    private Node head;
    private Node tail;
    private int N;
    
    public GeneralizedQueue()
    {
        head = null;
        tail = null;
        N = 0;
    }
    
    public boolean isEmpty()
    {
        return N == 0;
    }
    
    public void show()//遍历
    {
        Node current = head;
        while(current != null)
        {
            StdOut.print(current.item + "\t");
            current = current.next;
        }
        StdOut.print("\n");
    }
    
    public void insert(Item x)
    {
        Node node = new Node();
        node.item = x;
        node.next = null;
        if(this.isEmpty())
        {
            head = tail = node;
            N++;
            return;
        }
        tail.next = node;
        tail = node;
        N++;
    }
    
    public Item delete(int k)//删除第k项（从第0项开始）,并返回最近插入的一项
    {
        if(k < 0 || k > N)
        {
            return null;
        }
        if(k == 0)
        {
            head = head.next;
            N--;
            return tail.item;
        }
        Node current = head.next;
        Node before_current = head;
        for(int i = 0; i < k; i++)
        {
            current = current.next;
            before_current = before_current.next;
        }
        before_current.next = current.next;
        N--;
        Node p = head;
        while(p.next != null)
        {
            p = p.next;
        }
        tail = p;
        return tail.item;
    }
    
    public static void main(String[] args)
    {
        GeneralizedQueue<Integer> queue = new GeneralizedQueue<Integer>();
        for(int i = 0; i < 10; i++)
        {
            queue.insert(i);
        }
        queue.show();
        StdOut.println(queue.delete(3));
        queue.show();
    }
}

import edu.princeton.cs.algs4.*;

public class GeneralizedQueue<Item>
{
    private class Node
    {
        Item item;
        Node next;
    }
    
    private Node head;
    private Node tail;
    private int N;
    
    public GeneralizedQueue()
    {
        head = null;
        tail = null;
        N = 0;
    }
    
    public boolean isEmpty()
    {
        return N == 0;
    }
    
    public void show()//遍历
    {
        Node current = head;
        while(current != null)
        {
            StdOut.print(current.item + "\t");
            current = current.next;
        }
        StdOut.print("\n");
    }
    
    public void insert(Item x)
    {
        Node node = new Node();
        node.item = x;
        node.next = null;
        if(this.isEmpty())
        {
            head = tail = node;
            N++;
            return;
        }
        tail.next = node;
        tail = node;
        N++;
    }
    
    public Item delete(int k)//删除第k项,并返回最近插入的一项,从第0项开始
    {
        if(k < 0 || k > N)
        {
            return null;
        }
        if(k == 0)
        {
            head = head.next;
            N--;
            return tail.item;
        }
        Node current = head.next;
        Node before_current = head;
        for(int i = 0; i < k; i++)
        {
            current = current.next;
            before_current = before_current.next;
        }
        before_current.next = current.next;
        N--;
        Node p = head;
        while(p.next != null)
        {
            p = p.next;
        }
        tail = p;
        return tail.item;
    }
    
    public static void main(String[] args)
    {
        GeneralizedQueue<Integer> queue = new GeneralizedQueue<Integer>();
        for(int i = 0; i < 10; i++)
        {
            queue.insert(i);
        }
        queue.show();
        StdOut.println(queue.delete(3));
        queue.show();
    }
}