今天小弟我朋友的面试题…高手帮忙

今天我朋友的面试题……高手帮忙。
有a   b   c   d四个字符，用递归的方法将其能出现的组合打印出来。
如：
a   b   c   d
a   b   d   c
a   c   b   d
……

------解决方案--------------------
Option Explicit

Dim AData(4) As Integer

Private Sub PrintResult()
Dim iLoop As Integer
For iLoop = 0 To 3
Debug.Print Chr(AData(iLoop) + Asc( "a ")) & " ";
Next iLoop
Debug.Print
End Sub

Private Sub Try(ByVal iLevel As Integer)
Dim iLoop As Integer
Dim iFind As Integer
Dim bExist As Boolean
If iLevel > = 4 Then
PrintResult
Else
iLoop = 0
Do While iLoop <= 3
bExist = False
For iFind = 0 To iLevel - 1
If AData(iFind) = iLoop Then
bExist = True
Exit For
End If
Next iFind
If Not bExist Then
AData(iLevel) = iLoop
Try iLevel + 1
AData(iLevel) = -1
End If
iLoop = iLoop + 1
Loop
End If
End Sub

Private Sub Command1_Click()
Dim iLoop As Integer
For iLoop = 0 To 3
AData(iLoop) = -1
Next iLoop
Try (0)
End Sub