vba 隊列實作

總覺得不夠完善，先記錄下來，在使用中慢慢修改

' 隻能硬模仿java

Private ne As Node

'隻搜集ID
Private item As Variant


Property Let letNext(ByRef n As Node)
    Set ne = n
End Property

Property Let letItem(ByRef i As Variant)
    assign item, i
End Property

Property Get getNext()
 Set getNext = ne
End Property

Property Get getItem()
    assign getItem, item
End Property


Private Sub assign(ByRef x, ByVal y)

    If IsObject(y) Then
        Set x = y
    Else
        x = y
    End If

End Sub

           

' 隊列實作，FIFO模式

' 一直都是哨兵節點
Private head As Node

' 指向尾節點
Private last As Node

' 隊列數量
Private n As Integer

'哨兵節點
Private emptyNode As New Node


' 勉強當構造函數使用
Private Sub class_initialize()

    Set head = emptyNode
    Set last = emptyNode
    n = 0
End Sub


Public Function isEmpty() As Boolean
    isEmpty = head.getNext Is Nothing
End Function

Public Property Get size() As Integer
    size = n
End Property

'擷取首部元素，即最先進入隊列的元素，但是并不移除，僅僅檢視
Public Function peek() As String
    If isEmpty() Then Err.Raise 404, "Queue.peek", "請先添加在檢視"
    
    peek = head.getNext.getItem
    
End Function

'添加元素
Public Sub enqueue(ByRef s As Variant)
' 添加元素應該從尾部添加
    Dim newNode As New Node
    
    newNode.letItem = s
    
    last.letNext = newNode
    
    assign last, newNode
    
    n = n + 1

End Sub

'擷取應該出列的元素，并删除其元素
Public Function dequeue() As Variant
    
    Dim first As Node
    
    
    assign first, head.getNext
    
    assign dequeue, first.getItem

     head.letNext = first.getNext
    
    n = n - 1
    
    ' 如果全部取出，必須回歸到穩定狀态，即初始化狀态
    ' 思考：有沒有一種辦法，避免判斷，可以借用哨兵節點
    If isEmpty() Then assign last, emptyNode
    
End Function

Public Function hasNext() As Boolean
    hasNext = Not isEmpty()
End Function

Private Sub assign(ByRef x, ByVal y)

    If IsObject(y) Then
        Set x = y
    Else
        x = y
    End If

End Sub