c# - 我将如何在一个简单的有向图中倒数？

Question

所以我有这张图表，其中包含我正在遍历并打印出来的书籍。

public class Books : IBookFinder
{
    private Books(Books next, string book)
    {
        Next = next;
        Book = book;
    }

    public Books Next { get; }
    public string Book { get; }

    public Books Previous(string book)
    {
        return new Books(this, book);
    }

    public static Books Create(string book)
    {
        return new Books(null, book);
    }

    public string FromLeft(Books books, int numberFromLeft)
    {
        for (int i = 1; i < numberFromRight; i++)
        {
            books = books?.Next; //Go through the books and return null if books is null.
        }

        return books.book; //Should probably check for null here as it crashes if the input number is out of book range (something else than 1-4)
    }

    public string FromRight(Books books, int numberFromRight
    {
        //How to implement this bad boy?
    }
}

一切都很好，但我想实现一个 FromRight 方法，这样我就可以在给定数字输入的情况下，根据书在图中的位置写出书名。例如，如果输入“3”，它应该输出“指环王”。我该怎么做呢？非常感谢任何提示。

class Program
{
    static void Main(string[] args)
    {
        var curr = Books
            .Create("Harry Potter")
            .Previous("Lord of the Rings")
            .Previous("Twilight")
            .Previous("Da Vinci Code");

        while (curr != null)
        {
            if (curr.Next != null)
            {
                Console.Write(curr.Book + " --- ");
            }
            else
            {
                Console.WriteLine(curr.Book);
            }
            curr = curr.Next;
        }

        Console.WriteLine("Input number to pick a book");

        var bookNumber = Console.ReadLine();
        int n;

        if (int.TryParse(bookNumber, out n)) //Checking if the input is a #
        {

        }
        else
        {
            Console.WriteLine("Input was not a number!");
        }
        Console.WriteLine(bookNumber);

        Console.ReadLine();
    }
}

更新:

我已经设法找到一种方法来做到这一点，而不必制作双向链表，尽管这当然可能是解决此问题的最佳解决方案。

我创建了一个辅助函数 Count()，它获取列表并对条目进行计数:

    private int Count(Books books)
    {
        int count = 1;
        while (books.Next != null)
        {
            books = books.Next;
            count++;
        }

        return count;
    }

然后我使用此方法的返回值从右侧选择书籍:

    public string FromRight(Books books, int numberFromRight)
    {
        var bookCount = Count(books); //Getting the amount of books.
        for (int i = numberFromRight; i < bookCount; i++)
        {
            books = boos?.Next; 
        }

        return books.Book;
    }

Answer 1

由于您像创建链表一样创建它，因此要倒退，您需要创建一个双向链表:https://en.wikipedia.org/wiki/Doubly_linked_list

您当前的代码没有表示前一个节点。在创建下一个节点时将前一个节点设置为当前节点，然后它的迭代就像你最初做的那样。

迭代直到没有Next，然后打印直到没有previous。