java - 对链表方法内的日期进行排序

Question

我在待办事项列表 list2016 中添加了一堆日期，现在我需要按日期对这些待办事项列表项进行排序(最早的在前，最新的在最后)。

这一切都应该发生在我的 add 方法中，但我不知道如何做到这一点。有什么想法吗？

public class ToDoListEntry 
{
    String task;
    LocalDate date;
    ToDoListEntry next;

    public ToDoListEntry(LocalDate date, String task) 
    {
        this.task = task;
        this.date = date;
    }
}

接下来我尝试添加一个数组，但没有成功:

public class ToDoList 
{
    ToDoListEntry first;
    int size;

    public ToDoList ()
    {
        first = null;
        size = 0;
    }

    public void add(ToDoListEntry newTask) 
    {
        if (first == null)
        {
            first = newTask;
        }
        else
        {
            ToDoListEntry zeiger = first;
            while (zeiger.next != null)
            {
                zeiger = zeiger.next;
            }
            zeiger.next = newTask;
        }
        size++;
    }

    public String print()
    {
        String result = "";
        if (first == null) 
        {
            result = "Empty list!\n";
        } 
        else 
        {
            ToDoListEntry pointer = first;
            while (pointer != null) 
            {
                result += "Until " + pointer.date + " Task: " + pointer.task + "\n";
                pointer = pointer.next;
            }
        }
        System.out.println(result);
        return result;
    }
}

最后是主类。它应该创建一个新的 ToDoList 并将其打印出来(请注意，我没有包含 print() 方法):

public class MyMainClass
{
    public static void main(String[] args) 
    {
        System.out.println("Test 00: Empty List");
        ToDoList list2016 = new ToDoList();

        list2016.print(); 

        System.out.println("Test 01: add");
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 8, 15), "Do workout"));
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 6, 3), "Buy apples"));
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 10, 11), "Read Books"));
        list2016.print();
    }
}

Answer 1

这是一种低效且困惑的方式。然而，为了实现你想要的，我改变了你的两个类(class)。这些类是您的 ToDoList 类和 main 类。

ToDoList.java

import java.util.*;
import java.time.*;

public class ToDoList 
{
    ToDoListEntry first;
    ArrayList<LocalDate> datesList = new ArrayList();
    ArrayList<String> results = new ArrayList();

    public ToDoList ()
    {
        first = null;
    }

    public void add(ToDoListEntry newTask)
    {
        if (first == null)
        {
            first = newTask;
        }
        else
        {
            ToDoListEntry zeiger = first;
            while (zeiger.next != null)
            {
                zeiger = zeiger.next;
            }
            zeiger.next = newTask;
        }
    }

    public void sortDates()
    {
        Collections.sort(datesList);
    }

    public void compareAndSort()
    {
        ArrayList<String> tempDates = new ArrayList();
        for(LocalDate lD:datesList)
        {
            tempDates.add(lD+"");
        }
        ArrayList<String> tempSorted = new ArrayList();
        for(String s:tempDates)
        {
            for(String a:results)
            {
                if(a.contains(s))
                {
                    if(!tempSorted.contains(a))
                    {
                        tempSorted.add(a);
                    }
                }
            }
        }

        results=tempSorted;
        for(String s:results)
        {
            System.out.println(s);
        }
    }

    public String print()
    {
        String result = "";
        if (first == null) 
        {
            result = "Empty list!\n";
            System.out.println(result);
        }
        else 
        {
            ToDoListEntry pointer = first;
            while (pointer != null) 
            {
                result += "Until " + pointer.date + " Task: "+ pointer.task +"\n";
                if(LocalDate.now().isBefore(pointer.date))
                {
                    results.add("Until " + pointer.date + " Task: "+ pointer.task);
                }

                datesList.add(pointer.date);
                pointer = pointer.next;
            }
        }
        return result;
    }

    public String printDates()
    {
        String dates = datesList.toString();
        System.out.println(dates);
        return dates;
    }
}

Test.java(这就是您所描述的main类)

import java.util.*;
import java.time.*;

import java.util.*;
import java.time.*;

public class Test
{
    public static void main(String[] args)
    {
        System.out.println("Test 00: Empty List");
        ToDoList list2016 = new ToDoList();

        list2016.print(); 

        System.out.println("Test 01: add");
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 8, 15), "Do workout"));
        list2016.add(new ToDoListEntry(LocalDate.of(2015, 2, 18), "Hand in Homework"));
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 6, 3), "Buy apples"));
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 10, 11), "Read Books"));
        list2016.add(new ToDoListEntry(LocalDate.of(2016, 10, 11), "Read Homework"));

        list2016.print();
        list2016.sortDates();
        list2016.compareAndSort();
    }
}

我有两个笔记。

第一个是因为您特别说过最快，我添加了一个函数来删除已经超过当前日期的日期。如果您愿意，稍后可以通过更改 if 语句来更改此设置 if(LocalDate.now().isBefore(pointer.date))

其次，除非 first 为 null，否则您的 ToDoList.print() 实际上不再打印任何内容。