Function factorial(n As Integer) As Uinteger
    Return Iif(n = 0, 1, n * factorial(n - 1))
End Function

Sub swap_(s As String, i As Integer, j As Integer)
    Dim As String temp = Mid(s, i, 1)
    Mid(s, i, 1) = Mid(s, j, 1)
    Mid(s, j, 1) = temp
End Sub

Sub permute(s As String, l As Integer, r As Integer, perms() As String)
    If l = r Then
        Redim Preserve perms(Ubound(perms) + 1)
        perms(Ubound(perms)) = s
    Else
        For i As Uinteger = l To r
            swap_(s, l, i)
            permute(s, l + 1, r, perms())
            swap_(s, l, i) ' backtrack
        Next i
    End If
End Sub

Sub bubbleSort(arr() As String)
    Dim As Integer i, j, n = Ubound(arr)
    Dim As String temp

    For i = 0 To n - 1
        For j = 0 To n - i - 1
            If arr(j) > arr(j + 1) Then
                temp = arr(j)
                arr(j) = arr(j + 1)
                arr(j + 1) = temp
            End If
        Next j
    Next i
End Sub

Function nextHigh1(Byref n As String) As String
    Dim As String perms()
    Dim As Uinteger i, idx

    permute(n, 1, Len(n), perms())
    bubbleSort perms()
    Dim As Uinteger k = Ubound(perms)

    For i = 0 To k
        If perms(i) = n Then
            idx = i
            Exit For
        End If
    Next i

    Return Iif(idx < k, perms(idx + 1), "0")
End Function

Dim As String tests1(7) = {"0", "9", "12", "21", "12453", "738440", "45072010", "95322020"}
Dim As Double t0 = Timer
For i As Uinteger = 0 To Ubound(tests1)
    Print tests1(i); " => "; nextHigh1(tests1(i))
Next i
Print Chr(10); Timer - t0; "sec."