Imports System
Public Class PermutationsAndCombinations
' Swap two characters in an array
Private Shared Sub Swap(arr As Char(), i As Integer, j As Integer)
Dim tmp As Char = arr(i)
arr(i) = arr(j)
arr(j) = tmp
End Sub
' Print array of chars
Private Shared Sub PrintArray(arr As Char(), size As Integer)
For i As Integer = 0 To size - 1
Console.Write(arr(i) & " ")
Next
Console.WriteLine()
End Sub
' Recursive function to generate permutations
Private Shared Sub Permute(arr As Char(), l As Integer, r As Integer)
If l = r Then
PrintArray(arr, r + 1)
Return
End If
For i As Integer = l To r
Swap(arr, l, i)
Permute(arr, l + 1, r)
Swap(arr, l, i) ' backtrack
Next
End Sub
' Generate all combinations using bitmask
Private Shared Sub GenerateCombinations(arr As Char(), size As Integer)
For mask As Integer = 1 To (1 << size) - 1
For i As Integer = 0 To size - 1
If (mask And (1 << i)) <> 0 Then
Console.Write(arr(i) & " ")
End If
Next
Console.WriteLine()
Next
End Sub
Public Shared Sub Main(args As String())
Dim input As Char() = {"a"c, "b"c, "c"c}
Dim size As Integer = input.Length
Console.WriteLine("All permutations:")
Permute(input, 0, size - 1)
Console.WriteLine(Environment.NewLine & "All combinations:")
GenerateCombinations(input, size)
End Sub
End Class
' run:
'
' All permutations:
' a b c
' a c b
' b a c
' b c a
' c a b
' c b a
'
' All combinations:
' a
' b
' a b
' c
' a c
' b c
' a b c
'
