Recursion, multiple base cases in VBA

Question

I'm trying to take the first block of code from this link: http://www.geeksforgeeks.org/dynamic-programming-subset-sum-problem/ Copied and pasted below:

bool isSubsetSum(int set[], int n, int sum)
{
   // Base Cases
   if (sum == 0)
     return true;
   if (n == 0 && sum != 0)
     return false;

   // If last element is greater than sum, then ignore it
   if (set[n-1] > sum)
     return isSubsetSum(set, n-1, sum);

   /* else, check if sum can be obtained by any of the following
      (a) including the last element
      (b) excluding the last element   */
   return isSubsetSum(set, n-1, sum) || isSubsetSum(set, n-1, sum-set[n-1]);
}

And translate it into a recursive VBA function that I plan on calling from a Sub.

So far I have:

Function SubSum(source(), n As Integer, sum)

    If sum = 0 Then
        SubSum = True
    End If
    If (n = 0 And sum <> 0) Then
        SubSum = False
    End If

    If source(n - 1) > sum Then
        SubSum = SubSum(source, n - 1, sum)
    End If

    SubSum = (SubSum(source, n - 1, sum) Or SubSum(source, n - 1, sum - source(n - 1)))

End Function

My issue is that returning a value in each of the basecases doesn't exit that instance of the function. So when n=0 and sum<>0, SubSum is set equal to False and the function continues to the next if statement. The dataset I'm using is small and efficiency isn't an issue, I'm just trying to understand VBA's syntax.

After doing some research I found this post:Subset sum algorithm in vba But it doesn't implement it recursively.

`Function SubSum(source(), n As Integer, sum)` `If sum = 0 Then` SubSum = True GoTo RecurJump End If If (n = 0 And sum <> 0) Then SubSum = False GoTo RecurJump End If If source(n - 1) > sum Then SubSum = SubSum(source, n - 1, sum) GoTo RecurJump End If SubSum = (SubSum(source, n - 1, sum) Or SubSum(source, n - 1, sum - source(n - 1))) RecurJump: End Function ` — AdamY, Aug 05 '14 at 21:33
I couldn't figure out how to put code into the comments, but I found that this is a functional workaround, but the style is still VERY wrong. http://pastebin.com/0tMqyLnY If anyone finds something better, please let me know. I apologize if linking to pastebin is against the rules. — AdamY, Aug 05 '14 at 21:48

score 4 · Accepted Answer · answered Aug 05 '14 at 21:47

or use elseif to avoid exit function

Sub test()

Dim arr() As Variant
Dim sum As Long
Dim n As Long
Dim result As Boolean

    arr = Array(3, 34, 4, 12, 5, 2)
    n = 9
    result = SubSum(arr, UBound(arr), n)

End Sub


Function SubSum(source As Variant, n As Long, sum As Long) As Boolean

    If sum = 0 Then
        SubSum = True

    ElseIf (n = 0 And sum <> 0) Then
        SubSum = False

    ElseIf source(n - 1) > sum Then
        SubSum = SubSum(source, n - 1, sum)
    Else
        SubSum = (SubSum(source, n - 1, sum) Or SubSum(source, n - 1, sum - source(n - 1)))

    End If
End Function

Not that Exit Function should be avoided, wrong choice of words :) — , Aug 05 '14 at 21:53
I had edited my code but discarded it as you had already posted it :) — Siddharth Rout, Aug 05 '14 at 21:56

score 1 · Answer 2 · answered Aug 05 '14 at 21:45

My issue is ..... and the function continues to the next if statement.

To solve that problem you will have to use Exit Function.

For example

'
'~~> Rest of the code
'
If sum = 0 Then
    SubSum = True
    Exit Function   
ElseIf (n = 0 And sum <> 0) Then
    SubSum = False
    Exit Function
End If
'
'~~> Rest of the code
'

Recursion, multiple base cases in VBA

2 Answers2