Circular Permutation

[Juggler_IN]

I have a code for Permutations which I am unable to modify for Circular Permutations.

Example of circular permutation:
CircularPermute

What is need is that, for example with a set 1234, instead of all 24 items, the code should generate only the first 6 (which is (n-1)! = (4-1)! = 6).

Desired output:
1234
1243
1324
1342
1423
1432

Code:

Option Explicit

Public c As New Collection
Sub PTEST()

    Dim i
    Call PERMU("", "1234", 4)
    For i = 1 To c.count
        Debug.Print c.item(i)
    Next i
    Set c = Nothing

End Sub
Sub PERMU(ByVal x As String, _
          ByVal y As String, _
          ByVal k As Long)

    Dim s$
    Dim i%

    For i = 1 To Len(y)
        s = x & Mid(y, i, 1)
        If Len(s) = k Then
            On Error Resume Next
            c.Add s
            Err.Clear
            On Error GoTo 0
            On Error GoTo -1
        Else
        End If
        If Len(s) < k Then
            PERMU CStr(s), Left(y, i - 1) & Mid(y, i + 1), k
        End If
    Next i

End Sub

 

[jasonb75]

The simple way would be

Sub PTEST()

    Dim i
    Call PERMU("", "1234", 4)
    For i = 1 To WorksheetFunction.Fact(4 - 1)
        Debug.Print c.Item(i)
    Next i
    Set c = Nothing

End Sub

 

[Juggler_IN]

@jasonb75 ... this particular workaround I was able to implement, wanted to check if there was a proper way rather than a workaround.

 

[jasonb75]

The only other way would be to test each permutation before adding it to the collection, but given that the permutation has to be created before it can be tested I think it would be a false economy.

 

[Juggler_IN]

@jasonb75 ... there is a second aspect too ... the order of the subsets is different in circular as against permutation. That is, with the (n-1) edit we get:

1​	2​	3​	4​
1​	2​	4​	3​
1​	3​	2​	4​
1​	3​	4​	2​
1​	4​	2​	3​
1​	4​	3​	2​

But, across examples of circular the order of the sets is:

1​	2​	3​	4​
1​	3​	2​	4​
1​	4​	2​	3​
1​	4​	3​	2​
1​	2​	4​	3​
1​	3​	4​	2​

 

[jasonb75]

The edit matches your original example, which I believe is the default order of a collection. If you want something different then you will need a method that doesn't use collections.

You will also need to determine how the correct order is decided, there is no indication of that in the link that you provided, and the order of your second example above differs from the one in the link on all but the first and last rows.