Question

How can I write all possible combinations to the console? For example, if user enters abc, then it will write aaa, aab, aac, abb, abc, acc, bbb, bbc, ccc. Please help me.

Here’s some code:

    Dim abc() As String = {"a", "b", "c"} '      

    Sub Main()
        Console.WriteLine("Enter the amount of characters")
        Dim count As Integer = Console.ReadLine
        outputStrings("", count)

        Console.ReadLine()
    End Sub

    Private Sub outputStrings(ByVal startString As String, ByVal letterCount As Integer)
        For i = 0 To abc.Length - 1
            Dim temp As String = startString           
            temp += abc(i)
            If temp.Length = letterCount Then
                Console.WriteLine(temp)

                If i = abc.Length - 1 Then
                    Console.WriteLine("----")    
                End If
            Else
                outputStrings(temp, letterCount)
            End If

        Next
    End Sub

Something has to be done after the dashed lines to remove unwanted permutation to leave out only valid combinations.

Answer 1

You can restrict the letters used to ones at or to the right of abc(i) with an additional parameter abcIndex, and start the for loop from there. Only strings which have their letters in alphabetical order will be written, which prevents duplicates.

Private Sub outputStrings(ByVal startString As String, ByVal letterCount As Integer, ByVal abcIndex As Integer)
    For i = abcIndex To abc.Length - 1
        Dim temp As String = startString
        temp += abc(i)
        If temp.Length = letterCount Then
            Console.WriteLine(temp)
        Else
            outputStrings(temp, letterCount, i)
        End If
    Next
End Sub

Call with:

outputStrings("", 3, 0)