Public Function mergesort(ByVal m As List(Of Customer))
Dim left As New List(Of Customer)
Dim right As New List(Of Customer)
Dim middle As Integer
Dim aftermiddle As Integer
Dim result As New List(Of Customer)
If m.Count < 2 Then
'Already sorted
Return m
Else
'Sort here
middle = (m.Count - 1) / 2
aftermiddle = middle + 1
For t = 0 To middle
left.Add(m(t))
Next t
For y = aftermiddle To m.Count - 1
right.Add(m(y))
Next y
left = mergesort(left)
right = mergesort(right)
result = merge(left, right)
Return result
End If
End Function
Function merge(ByVal l As List(Of Customer), ByVal r As List(Of Customer))
Dim result As New List(Of Customer)
While l.Count > 0 And r.Count > 0
If l(0).Name <= r(0).Name Then
result.Add(l(0))
l.RemoveAt(0)
Else
result.Add(r(0))
r.RemoveAt(0)
End If
End While
If l.Count > 0 Then
result.Add(l(0))
l.RemoveAt(0)
End If
If r.Count > 0 Then
result.Add(r(0))
r.RemoveAt(0)
End If
Return result
End Function
Merge sort problem (VB.net)
Author
Im having trouble implementing a Mergesort routine on a List in VB.net. It sorts the first time, but subsequent sorts reduce the list size. This might just be because Im translating pseudocode. Im more suited to C++ so could someone give this a quick glance and tell me where Im going wrong?
The site im using for reference
http://www.codecodex.com/wiki/Merge_sort#Pseudocode
Chars
The one gotcha that might be getting you is vb's rounding - Most languages truncate values, vb does banker's rounding - so when you do middle = (m.Count - 1) / 2
, you might want to try doing math.truncate(middle = (m.Count - 1) / 2) and see if that fixes your issue.
, you might want to try doing math.truncate(middle = (m.Count - 1) / 2) and see if that fixes your issue.
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