快速排序 - 运行时错误

Question

我遇到了一些我知道缺少TheList数组的编程代码，但无法确定将其放在何处。这来自修订剑桥教科书（第174页），似乎不完整。我只是坚持Sub Main()，因为它说你不能省略它。任何伟大的想法将不胜感激！

Module Module1
Dim TheList(20) As Integer
Sub Main()

    TheList(1) = 20
    TheList(2) = 2
    TheList(3) = 22
    TheList(4) = 4
    TheList(5) = 5
    TheList(6) = 28
    TheList(7) = 21
    TheList(8) = 6
    TheList(9) = 19
    TheList(10) = 18
    TheList(11) = 7
    TheList(12) = 16
    TheList(13) = 8
    TheList(14) = 56
    TheList(15) = 92
    TheList(16) = 1
    TheList(17) = 3
    TheList(18) = 42
    TheList(19) = 76
    TheList(20) = 84

    Call SelectionSort()
    Call DisplayList()

End Sub

Sub DisplayList()
    Dim Index As Integer

    Console.WriteLine()
    For Index = 1 To 20
        Console.Write(TheList(Index) & " ")
    Next
End Sub


Sub SelectionSort()
    Dim SortedListPosn, InsertPosn, SortedPosn As Integer
    Dim Index, ShufflePosn As Integer
    Dim CurrentValue As Integer
    Dim InsertPosnFound As Boolean

    For Index = 2 To 9
        CurrentValue = TheList(Index)
        SortedListPosn = 1
        InsertPosnFound = False
        Do
            If CurrentValue > TheList(SortedPosn) Then
                SortedListPosn = SortedListPosn + 1
            Else
                InsertPosn = SortedListPosn
                InsertPosnFound = True
            End If

        Loop Until InsertPosnFound = True

        For ShufflePosn = Index To (InsertPosn + 1) Step -1
            TheList(ShufflePosn) = TheList(ShufflePosn - 1)
        Next
        TheList(InsertPosn) = CurrentValue
    Next

End Sub

结束模块

Answer 1

你的问题是你的SelectionSort，当我调试它时，它最终会抛出“算术运算导致溢出”。

你需要自己编写吗？ VB.Net已经内置了可以做你想做的库。例如，您可以使用Array.Sort（TheList）。

Module Module1
    Dim TheList(20) As Integer
    Sub Main()

        TheList(1) = 20
        TheList(2) = 2
        TheList(3) = 22
        TheList(4) = 4
        TheList(5) = 5
        TheList(6) = 28
        TheList(7) = 21
        TheList(8) = 6
        TheList(9) = 19
        TheList(10) = 18
        TheList(11) = 7
        TheList(12) = 16
        TheList(13) = 8
        TheList(14) = 56
        TheList(15) = 92
        TheList(16) = 1
        TheList(17) = 3
        TheList(18) = 42
        TheList(19) = 76
        TheList(20) = 84

        'Call SelectionSort()
        Array.Sort(TheList)

        Call DisplayList()

        ' Put this to pause the console window from closing, then just press the ENTER key
        Console.ReadLine()

    End Sub

    Sub DisplayList()
        Dim Index As Integer

        Console.WriteLine()
        For Index = 1 To 20
            Console.Write(TheList(Index) & " ")
        Next
    End Sub
    End Module

结果：

修改

那么我们如何修复选择排序......试一试......

Module Module1
    Dim TheList(20) As Integer
    Sub Main()

        TheList(1) = 20
        TheList(2) = 2
        TheList(3) = 22
        TheList(4) = 4
        TheList(5) = 5
        TheList(6) = 28
        TheList(7) = 21
        TheList(8) = 6
        TheList(9) = 19
        TheList(10) = 18
        TheList(11) = 7
        TheList(12) = 16
        TheList(13) = 8
        TheList(14) = 56
        TheList(15) = 92
        TheList(16) = 1
        TheList(17) = 3
        TheList(18) = 42
        TheList(19) = 76
        TheList(20) = 84

        Call SelectionSort()
        ' Call QuickSort(1, 20)
        Call DisplayList()

        Console.ReadLine()
    End Sub

    Sub DisplayList()
        Dim Index As Integer

        Console.WriteLine()
        For Index = 1 To 20
            Console.Write(TheList(Index) & " ")
        Next
    End Sub


    Sub SelectionSort()
        Dim CurrentIndex, NextIndex, SmallestValueIndex, TempValue As Integer

        For CurrentIndex = 1 To 20
            SmallestValueIndex = CurrentIndex
            For NextIndex = CurrentIndex + 1 To 20
                ' Find a number in the list that's the smallest to swap into the current position
                If TheList(NextIndex) < TheList(SmallestValueIndex) Then
                    SmallestValueIndex = NextIndex
                End If
            Next

            ' Swap the current index location with the smallest's value location
            TempValue = TheList(CurrentIndex)
            TheList(CurrentIndex) = TheList(SmallestValueIndex)
            TheList(SmallestValueIndex) = TempValue
        Next
    End Sub

    Sub QuickSort(ByVal Left As Integer, ByVal Right As Integer)
        Dim I As Integer = Left
        Dim J As Integer = Right
        Dim Pivot As Integer = TheList((Left + Right) / 2)

        While I <= J
            While TheList(I) < Pivot
                I = I + 1
            End While

            While TheList(J) > Pivot
                J = J - 1
            End While

            If I <= J Then
                ' Swap
                Dim Temp = TheList(I)
                TheList(I) = TheList(J)
                TheList(J) = Temp

                I = I + 1
                J = J - 1
            End If
        End While

        ' Recursion
        If Left < J Then
            QuickSort(Left, J)
        End If

        If I < Right Then
            QuickSort(I, Right)
        End If
    End Sub
End Module

结果（选择排序）：

结果（快速排序）：