' version 31-03-2017
' compile with: fbc -s console

Sub perms(n As ULong)

    Dim As Long p(n), i, k, s = 1

    For i = 1 To n
        p(i) = -i
    Next

    Do
        Print "Perm: [ ";
        For i = 1 To n
            Print Abs(p(i)); " ";
        Next
        Print "] Sign: "; s

        k = 0
        For i = 2 To n
            If p(i) < 0 Then
                If Abs(p(i)) > Abs(p(i -1)) Then
                    If Abs(p(i)) > Abs(p(k)) Then k = i
                End If
            End If
        Next

        For i = 1 To n -1
            If p(i) > 0 Then
                If Abs(p(i)) > Abs(p(i +1)) Then
                    If Abs(p(i)) > Abs(p(k)) Then k = i
                End If
            End If
        Next

        If k Then
            For  i = 1 To n
                If Abs(p(i)) > Abs(p(k)) Then p(i) = -p(i)
            Next
            i = k + Sgn(p(k))
            Swap p(k), p(i)
            s = -s
        End If

    Loop Until k = 0

End Sub

' ------=< MAIN >=------

perms(3)
print
perms(4)

' empty keyboard buffer
While Inkey <> "" : Wend
Print : Print "hit any key to end program"
Sleep
End