Question

我无法理解为什么这种合并排序会导致堆栈溢出。是因为我没有基本情况，如果是这样，我将如何添加它？对于像我这样的初学者来说，合并排序非常先进:(所以我希望得到任何帮助或建议。此外，一旦您以递归方式拆分数组，我无法理解数据的存储位置。我明白拆分原始数组会将其分解为单个元素，但这些元素存储在哪里？

Sub Main()
    Dim Array() As Integer = {5, 4, 3, 1, 2, 6}
    Dim right As Integer = Array.Length - 1 'find right index
    Dim left As Integer = 0 'set left index
    mergeSort(Array, left, right)
End Sub

Sub mergeSort(Array, left, right)
    Dim middle As Integer
    If left < right Then
        middle = (left + right) / 2

        'recursively split both halves of the array
        mergeSort(Array, left, middle)
        mergeSort(Array, middle + 1, right)

        'sort individual elements
        mergeSortedArray(Array, left, middle, middle + 1, right)
    End If
End Sub

Sub mergeSortedArray(ByRef Array, left, middle, rbeg, right)
    Dim pt As Integer = 0
    Dim TempArray(6)

    While (left <= middle) And (rbeg <= right) 'sort every element
        If Array(left) < Array(rbeg) Then
            TempArray(pt) = Array(left)
            left += 1
        Else
            TempArray(pt) = Array(rbeg)
            rbeg += 1
        End If
        pt += 1
    End While

    If left > middle Then
        While rbeg <= right   'left sub array exhausted 
            TempArray(pt) = Array(rbeg)
            rbeg += 1
            pt += 1
        End While
    Else
        While left <= middle   'right sub array exhausted 
            TempArray(pt) = Array(left)
            left += 1
            pt += 1
        End While
    End If

    For Each element In TempArray
        Console.WriteLine(element & " ")
    Next
End Sub

Answer 1

此代码存在很多问题。 VB中的合并排序看起来更像是这样：

Sub Main()
    Dim Array() As Integer = {5, 33, 3, 10, 2} 'make the array

    'Split Array: you need the leftmost index & rightmost index
    Split(Array, 0, 4)
    Console.ReadKey()

End Sub

Sub Split(Array, left, right)
    If left < right Then 'if the array has elements..
        Dim middle As Integer = (left + right) \ 2 'find halfway point 

        Split(Array, left, middle) 'split left array 

        Split(Array, middle + 1, right) 'split right array 
        'recursion keeps on splitting the two arrays until we have a bunch of single elements

        'now sort and merge
        Merge(Array, left, middle, right)
    End If
End Sub
Sub Merge(ByRef Array, left, middle, right)

    Dim SizeA As Integer = middle - left + 1
    Dim SizeB As Integer = right - middle
    Dim LeftArray(SizeA) As Integer 'set size of left array.
    Dim RightArray(SizeB) As Integer 'set size of right array

    'Left & Right pointers to keep track of what elements in the array we are referring to
    Dim LP As Integer
    Dim RP As Integer

    For LP = 0 To SizeA - 1
        LeftArray(LP) = Array(left + LP) 'assign 0 index of original array to left hand array (5)
    Next

    For RP = 0 To SizeB - 1
        RightArray(RP) = Array(middle + 1 + RP) 'assign 1 index of original array to right hand array (33)
    Next

    'reset pointers
    LP = 0
    RP = 0
    Dim i = left 'set a pointer for the original array

    'swap elements if need be:
    While LP < SizeA And RP < SizeB
        If LeftArray(LP) <= RightArray(RP) Then 'if element in left array is smaller that the one in the right
            Array(i) = LeftArray(LP) 'assign the left value to the original array
            LP += 1 ' increment the left array's pointer
        Else
            Array(i) = RightArray(RP) 'otherwise the original array gets the right element
            RP += 1 'increment the right array's pointer
        End If
        i += 1 'now increment the counter for our new array
    End While

    'Hang on...what if there are still elements in the left array
    While LP < SizeA
        Array(i) = LeftArray(LP) 'assign these elements to the new array
        LP += 1 'increment the left pointer
        i += 1 'increment the new array's pointer
    End While

    'Hang on...what if there are still elements in the right array
    While RP < SizeB
        Array(i) = RightArray(RP) 'assign these elements to the new array
        RP += 1 'increment the right pointer
        i += 1 'increment the new array's pointer
    End While

    'write out the new array
    For Each element In Array
        Console.Write(element & " ")
    Next
    Console.WriteLine("")
    'start the second pass
End Sub

合并排序会创建堆栈溢出

1 个答案: