Question

我正在尝试使用Pop和Push功能创建链接列表堆栈。 Push方法正在运行，但Pop不是。我无法弄清楚在哪里返回其中的值，我认为它应该在整理出来时有用（对不起的措辞很抱歉）。

这是我的代码：

class Program
{

    int nextFree;
    int End;
    int Start;
    Names[] Stack;
    Names greg = new Names();
    Names matt = new Names();
    Names jack = new Names();
    Names fred = new Names();

    public struct Names
    {
        public Int32 pointer;
        public string data;
    }

    static void Main(string[] args)
    {

        Program prog = new Program();
        do
        {
            prog.DisplayMenu();
        }
        while (true);
    }

    public void DisplayMenu()
    {
        Int32 userInput = 0;

        Console.WriteLine("Linear Stack");
        Console.WriteLine("1: Add to stack");
        Console.WriteLine("2: Delete from stack");
        userInput = Int32.Parse(Console.ReadLine());


        switch (userInput)
        {
            case 1:
                this.Push();
                break;
            case 2:
                this.Pop();
                break;
        }

    }

     public Program() 
    {
       Stack = new Names[6];

        greg.data = "Greg";
        greg.pointer = 1;

        matt.data = "Matt";
        matt.pointer = 2;

        jack.data = "Jack";
        jack.pointer = 3;

        fred.data = "Fred";
        fred.pointer = -1;

        Stack[0] = greg;
        Stack[1] = matt;
        Stack[2] = jack;
        Stack[3] = fred;
        nextFree = 4;
        End = 5;
        Start = 0;
    }


     public string Pop()
     {

         string value = string.Empty;

         if (nextFree == -1)
         {
             Console.WriteLine("Stack is empty");
             Console.ReadLine();
         }
         else
         {
             Names thisNode = Stack[End];
             int temp = End;
             End = thisNode.pointer;
             thisNode.pointer = nextFree;
             nextFree = temp;
         }
         this.ListAllNames();
         return value;
     }

     public void Push()
     {
         if (nextFree >= Stack.Length)
         {
             Console.WriteLine("Stackoverflow, to many elements for the stack");
             Console.ReadLine();
         }
         else
         {
             Console.WriteLine("Enter a name to be added");
             string input = Console.ReadLine();
             Stack[nextFree].data = input;
             Stack[nextFree].pointer = End;
             End = nextFree;
             nextFree++;     
         }
            this.ListAllNames();
     }


     public void ListAllNames()
     {
         foreach (Names name in Stack)
         {
             Console.WriteLine("Name:" + name.data);
         }
     }



 }
}

Answer 1

我强烈建议您阅读Eric Lippert's Immutable Stack文章。它将为您提供一些有关实施的非常有趣的提示。

以下是代码：

public interface IStack<T> : IEnumerable<T>
{
    IStack<T> Push(T value);
    IStack<T> Pop();
    T Peek();
    bool IsEmpty { get; }
}

public sealed class Stack<T> : IStack<T>
{
    private sealed class EmptyStack : IStack<T>
    {
        public bool IsEmpty { get { return true; } }
        public T Peek() { throw new Exception("Empty stack"); }
        public IStack<T> Push(T value) { return new Stack<T>(value, this); }
        public IStack<T> Pop() { throw new Exception("Empty stack"); }
        public IEnumerator<T> GetEnumerator() { yield break; }
        IEnumerator IEnumerable.GetEnumerator() { return this.GetEnumerator(); }
    }
    private static readonly EmptyStack empty = new EmptyStack();
    public static IStack<T> Empty { get { return empty; } }
    private readonly T head;
    private readonly IStack<T> tail;
    private Stack(T head, IStack<T> tail)
    {
        this.head = head;
        this.tail = tail;
    }
    public bool IsEmpty { get { return false; } }
    public T Peek() { return head; }
    public IStack<T> Pop() { return tail; }
    public IStack<T> Push(T value) { return new Stack<T>(value, this); }
    public IEnumerator<T> GetEnumerator()
    {
        for(IStack<T> stack = this; !stack.IsEmpty ; stack = stack.Pop())
            yield return stack.Peek();
    }
    IEnumerator IEnumerable.GetEnumerator() {return this.GetEnumerator();}
}

Answer 2

你不是非常面向对象的。正如Niklaus Wirth指出的那样：

对象=数据+算法

您需要封装内容，例如：

public class LinkedListStack<T>
{
  /// <summary>
  /// indicates whether or not the stack contains data
  /// </summary>
  public bool HasData { get { return this.Top != null ; } }

  /// <summary>
  /// The topmost stack frame
  /// </summary>
  private Node Top { get ; set; }

  /// <summary>
  /// constructor
  /// </summary>
  public LinkedListStack()
  {
    this.Top   = null ;
    return ;
  }

  /// <summary>
  /// constructor: initializes the stack with the provied contents.
  /// </summary>
  /// <param name="data"></param>
  public LinkedListStack( IEnumerable<T> data ) : this()
  {
    if ( data == null ) throw new ArgumentNullException("data") ;
    foreach ( T datum in data )
    {
      Push(datum) ;
    }
  }

  /// <summary>
  /// remove the top item from the stack and return it
  /// </summary>
  /// <returns></returns>
  public T Pop()
  {
    if ( this.Top == null ) throw new InvalidOperationException("Can't pop an empty stack!");
    Node top = this.Top ;
    this.Top = top.Next ;
    return top.Payload ;
  }

  /// <summary>
  /// push an item onto the stack
  /// </summary>
  /// <param name="datum"></param>
  public void Push( T datum )
  {
    this.Top = new Node( datum , this.Top ) ;
    return ;
  }

  /// <summary>
  /// private helper class (our stack frame)
  /// </summary>
  private class Node
  {
    public Node Next    ;
    public T    Payload ;
    public Node( T payload ) : this(payload,null)
    {
      return ;
    }
    public Node( T payload , Node next )
    {
      this.Next = next ;
      this.Payload = payload ;
      return ;
    }
  }

}

链接列表堆栈Pop方法

2 个答案: