permutation generator help.

[chandrans]

I have come across this permutation generator code. But doesn'
understand it
Can anybody explain how this works?
where x will be the string input and y will be initially ""
Sub GetPermutation(x As String, y As String)
' The source of this algorithm is unknown

Dim i As Integer, j As Integer
j = Len(y)
If j < 2 Then
Cells(CurrentRow, 1) = x & y
CurrentRow = CurrentRow + 1
Else
For i = 1 To j
Call GetPermutation(x + Mid(y, i, 1), Left(y, i - 1)
Right(y, j - i))
Next
End If
End Su

 

[keepITcool]

it's a recursive procedure. (which calls itself)
NOTE the description you give of the initial arguments s/b reversed!

to run it you'd call it like:

Dim currentrow As Long

Sub Foo()
currentrow = 1
Call GetPermutation("", "ABCDEF")
End Sub

and it will run the 720 (=PERMUT(6,5) permutations of the
letters "A thru F"

 

[Tom Ogilvy]

The code probably came from John Walkenbach's site:

http://j-walk.com/ss/excel/tips/tip46.htm

if not, that is a good place to start.