算法（Algorithms）第4版 练习 1.3.219

方法实现：

　　//1.3.19
    /**
     * remove the last node in the linked list whose first node is first
     * 
     * @return return the item of the last node
     * @throws NoSuchElementException if this Linked List is empty
     */
    public Item removeTheLast() {
        
        Node<Item> precurrent;
        Item item = null;
        
        precurrent = findPreLastNode();
        
        //has not found
        if(precurrent.next == null) {
            throw new NoSuchElementException("LinkedList is empty");
        }
        
        item = precurrent.next.item;
        //some implementation will add one empty node as head, and head.next = first
        //if so, it's not necessary to have if condition here
        if(precurrent.next == first)
            first = first.next;
        else
            precurrent.next = precurrent.next.next;
        
        return item;    
    }
    
    /**
     * return the previous last node
     * 
     * @return return the previous last node. 
     * If the last node is the first node, the previous last node is a virtual one
     */
    private Node<Item> findPreLastNode() {
        
        Node<Item> precurrent = new Node<Item>();
        precurrent.next = first;
        
        //find the previous last node
        //precurrent.next is the same as current
        while(precurrent.next != null && precurrent.next.next != null) {
            precurrent = precurrent.next;
        }
        
        return precurrent;
    }

 

 

测试用例：

package com.qiusongde.linkedlist;

import edu.princeton.cs.algs4.StdIn;
import edu.princeton.cs.algs4.StdOut;

public class Exercise1319 {

    public static void main(String[] args) {
        LinkedList<String> list = new LinkedList<String>();
        
        while(!StdIn.isEmpty()) {
            String s = StdIn.readString();
            list.insertAtBeginning(s);
            StdOut.println("insertAtBeginning success: " + s);
            StdOut.println(list);
        }
        
        String s = list.removeTheLast();
        StdOut.println("removeTheLast success: " + s);
        StdOut.println(list);
        
    }

}

 

 

测试数据1：

to
be
or
not
to
be

 

 

输出结果：

insertAtBeginning success: to
to 
insertAtBeginning success: be
be to 
insertAtBeginning success: or
or be to 
insertAtBeginning success: not
not or be to 
insertAtBeginning success: to
to not or be to 
insertAtBeginning success: be
be to not or be to 
removeTheLast success: to
be to not or be 

 

 

测试数据2：

to

 

 

输出结果：

insertAtBeginning success: to
to 
removeTheLast success: to

 

 

测试数据3：

输入为空

 

输出结果：

Exception in thread "main" java.util.NoSuchElementException: LinkedList is empty
    at com.qiusongde.linkedlist.LinkedList.removeTheLast(LinkedList.java:73)
    at com.qiusongde.linkedlist.Exercise1319.main(Exercise1319.java:18)