# VB.NET - Code Samples - Permutation Code

## VB.NET Permutation Algorithm

### Synopsis:

Used to create all the permutations or unique arrangements of a given set of letters e.g.("cat","cta","atc","act","tca","tac")

### The Reason:

Initially I needed a permutation algorithm to create all the possible combinations of letters so I could unscramble words. Most of the code samples I found involved recursion which seemed to be a memory hog and crashed my application quite frequently. I finally found some code that utilized a transposition matrix. The code was written in VB 6 by Ziad Cassim. I based my code on this aiming for readablity over efficiency. Most of my logic though was more directly pulled from the information on how to create the matrix. Go here for more information.

### The Code:

```Private Function Permutations(ByVal data As String) As String(,)
Dim i As Int32
Dim y As Int32
Dim x As Int32
Dim tempChar As String
Dim newString As String
Dim strings(,) As String
Dim rowCount As Long

If data.Length < 2 Then
Exit Function
End If

'use the factorial function to determine the number of rows needed
'because redim preserve is slow
ReDim strings(data.Length - 1, Factorial(data.Length - 1) - 1)
strings(0, 0) = data

'swap each character(I) from the second postion to the second to last position
For i = 1 To (data.Length - 2)
'for each of the already created numbers
For y = 0 To rowCount
'do swaps for the character(I) with each of the characters to the right
For x = data.Length To i + 2 Step -1
tempChar = strings(0, y).Substring(i, 1)
newString = strings(0, y)
Mid(newString, i + 1, 1) = newString.Substring(x - 1, 1)
Mid(newString, x, 1) = tempChar
rowCount = rowCount + 1
strings(0, rowCount) = newString
Next
Next
Next

'Shift Characters
'for each empty column
For i = 1 To data.Length - 1
'move the shift character over one
For x = 0 To strings.GetUpperBound(1)
strings(i, x) = strings(i - 1, x)
Mid(strings(i, x), i, 1) = strings(i - 1, x).Substring(i, 1)
Mid(strings(i, x), i + 1, 1) = strings(i - 1, x).Substring(i - 1, 1)
Next
Next

Return strings

End Function

Public Function Factorial(ByVal Number As Integer) As String
Try
If Number = 0 Then
Return 1
Else
Return Number * Factorial(Number - 1)
End If
Catch ex As Exception
Return ex.Message
End Try
End Function
```