vb.net 中的双哈希表或双哈希哈希表

Question

我试图在 vb.net 中创建一个双重散列哈希表，但遇到一些我不知道如何解决的错误。希望你们能帮助我。我遇到的问题是在任何有 dbnull.value 或 mod= 的地方，我在编辑器中遇到错误，但我不知道如何修复它们。把这段代码放在VB中看看我的意思。 这是代码：

Public Class DoubleHashing

Class DataItem
    Private data As Integer

    Public Sub New(ByVal i As Integer)
        data = i
    End Sub
    Public Function getKey() As Integer
        Return data
    End Function

End Class

Private hashArray() As DataItem
Private arraySize As Integer
Private bufItem As DataItem

Public Sub New(ByVal size As Integer)

    arraySize = size
    hashArray(arraySize) = New DataItem(arraySize)
    Dim bufItem(-1) As DataItem
End Sub

Public Function hashFunc1(ByVal key As Integer) As Integer
    Return key Mod arraySize
End Function

Public Function hashFunc2(ByVal key As Integer) As Integer
    Return 6 - key Mod 6
End Function


Public Sub insert(ByVal key As Integer, ByVal item As DataItem)
    Dim hashVal As Integer = hashFunc1(key) ' hash the key
    Dim stepSize As Integer = hashFunc2(key) ' get step size

    ' until empty cell or -1
    While hashArray(hashVal) <> DBNull.Value & hashArray(hashVal).getKey() <> -1
        hashVal += stepSize ' add the step
        hashVal mod= arraySize ' for wraparound
    End While
    hashArray(hashVal) = item ' insert item

End Sub

Public Function delete(ByVal key As Integer) As DataItem
    Dim hashVal As Integer = hashFunc1(key)
    Dim stepSize As Integer = hashFunc2(key) ' get step size

    While hashArray(hashVal) <> DBNull.Value
        If hashArray(hashVal).getKey() = key Then
            Dim temp As DataItem = hashArray(hashVal) ' save item
            hashArray(hashVal) = bufItem '  delete item
            Return temp '  return item
        End If

        hashVal += stepSize ' add the step
        hashVal mod= arraySize '  for wraparound
    End While

    Return DBNull.Value
End Function

Public Function find(ByVal key As Integer) As DataItem
    Dim hashVal As Integer = hashFunc1(key)
    Dim stepSize As Integer = hashFunc2(key)

    While hashArray(hashVal) <> DBNull.Value
        If hashArray(hashVal).getKey() = key Then
            Return hashArray(hashVal)
        End If

        hashVal += stepSize
        hashVal mod= arraySize
    End While

    Return DBNull.Value
End Function

结束类

Answer 1

通常第二个哈希函数绝不能返回 0。

我不认为 DBNull.Value 继承自 DataItem。此外，您的数组被初始化为某个大小的数组，其中包含对 Nothing 的引用。