vb.net - 通过重复获得组合

Question

如何将所有可能的组合写入控制台？例如，如果用户输入abc，那么它会写成aaa, aab, aac, abb, abc, acc, bbb, bbc, ccc。请帮助我。

这是一些代码:

    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

必须在虚线之后做一些事情来移除不需要的排列，从而只留下有效的组合。

Answer 1

您可以使用附加参数 abcIndex 将使用的字母限制为 abc(i) 或右侧的字母，并从那里开始 for 循环。只有字母按字母顺序排列的字符串才会被写入，这样可以防止重复。

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

调用:

outputStrings("", 3, 0)