Vb.net net字符串排列。排列还是组合？

我有很多这样的字符串

C-F-A-M

。我想根据该条件创建一个组合：

最后一个字符旁边的其他项目必须与最后一个字符组合

不允许有相同的组合，即使顺序不同。比如说

FC-M

CF-M

如果字符串数组包含>=3个元素，它将生成2&3个itemset；如果包含2个元素，它将只生成2个itemset

下面是我的代码。我的代码生成的结果与图片的右侧部分类似

我的问题是我应该用什么方法？它是排列、组合还是其他东西？ 在伪代码中，我的情况会是什么样

这是我的密码

Public Class permute
Dim ItemUsed() As Boolean
Dim pno As Long, pString As String
Dim inChars() As Char = {"c", "f", "a", "m"}

Private Sub permute_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load  
End Sub

Sub Permute(ByVal K As Long)
    ReDim ItemUsed(K)
    pno = 0

    Dim i As Integer
    For i = 2 To K
        Permutate(i, 1)
        tb.Text = K
    Next
End Sub

Private Sub Permutate(ByVal K As Long, ByVal pLevel As Long)
    Dim i As Long, Perm As String
    Perm = pString

    For i = 0 To K - 1
        If Not ItemUsed(i) Then
            If pLevel = 1 Then
                pString = inChars(i)
            Else
                pString += inChars(i)
            End If
            If pLevel = K Then
                pno = pno + 1
                Results.Text += _
                pno & " " & " = " & " " & pString & vbCrLf
                Exit Sub
            End If

            ItemUsed(i) = True
            Permutate(K, pLevel + 1)
            ItemUsed(i) = False
            pString = Perm
        End If
    Next
End Sub

Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
    Permute(tb.Text)
End Sub

Private Sub tb_TextChanged(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles tb.TextChanged
    If tb.Text = "" Then
        Results.Text = ""
    Else
        Permute(tb.Text)
    End If
End Sub
End Class

这是要求截图

这是节目截图

这似乎是一个组合问题，而不是排列问题：

“在数学中，组合是从一个更大的组中选择若干事物的一种方式，其中（与排列不同）顺序并不重要”。[]

尝试通过对数组中除最后一项之外的所有项进行组合来解决此问题。或者换句话说，对所有k执行组合操作nCk，使用

• n=输入数组的大小减去最后一项
• k=输出项集的大小，最小k为1，最大为n

然后将每个组合结果附加到最后一项。下面是伪代码，使用C#语法：p

var input = new char[] {'C', 'F', 'A', 'M'};

//save last char
var lastChar = input[input.Length - 1];
//combinationInput is input member without the last character
var combinationInput = new char[input.Length - 1];
Array.Copy(input, 0, combinationInput, 0, combinationInput.Length);

//generate output with itemset size 1 to combinationInput.Length
for (int i = 1; i <= combinationInput.Length; i++)
{
    //generate combination with size i
    var combinationOutput = combinationInput.Combinations(i);
    foreach (var combinedChar in combinationOutput)
    {
        //print output as: combinationOutput item + lastChar
        Console.WriteLine(string.Join(", ", combinedChar) + ", " + lastChar);
    }
}

var input=newchar[]{'C'，'F'，'A'，'M'}；
//保存最后一个字符
var lastChar=input[input.Length-1]；
//combinationInput是没有最后一个字符的输入成员
var combinationInput=新字符[input.Length-1]；
复制（输入，0，combinationInput，0，combinationInput.Length）；
//将itemset大小为1的输出生成为combinationInput.Length
对于（int i=1；i将此类添加到项目中：

Public NotInheritable Class Permutation

    Public Shared Function Create(array As Char()) As List(Of String)
        Return Permutation.Create(array, False)
    End Function

    Public Shared Function Create(array As Char(), sort As Boolean) As List(Of String)
        If (array Is Nothing) Then
            Throw New ArgumentNullException("array")
        ElseIf ((array.Length < 0) OrElse (array.Length > 13)) Then
            Throw New ArgumentOutOfRangeException("array")
        End If
        Dim list As New List(Of String)
        Dim n As Integer = array.Length
        Permutation.Permute(list, array, 0, array.Length)
        If (sort) Then
            list.Sort()
        End If
        Return list
    End Function

    Private Shared Sub Permute(list As List(Of String), array As Char(), start As Integer, n As Integer)
        Permutation.Print(list, array, n)
        If (start < n) Then
            Dim i, j As Integer
            For i = (n - 2) To start Step -1
                For j = (i + 1) To (n - 1)
                    Permutation.Swap(array, i, j)
                    Permutation.Permute(list, array, (i + 1), n)
                Next
                Permutation.RotateLeft(array, i, n)
            Next
        End If
    End Sub

    Private Shared Sub Print(list As List(Of String), array As Char(), size As Integer)
        If (array.Length <> 0) Then
            Dim s As Char() = New Char(size - 1) {}
            For i As Integer = 0 To (size - 1)
                s(i) = array(i)
            Next
            list.Add(s)
        End If
    End Sub

    Private Shared Sub RotateLeft(array As Char(), start As Integer, n As Integer)
        Dim tmp As Char = array(start)
        For i As Integer = start To (n - 2)
            array(i) = array(i + 1)
        Next
        array(n - 1) = tmp
    End Sub

    Private Shared Sub Swap(array As Char(), i As Integer, j As Integer)
        Dim tmp As Char
        tmp = array(i)
        array(i) = array(j)
        array(j) = tmp
    End Sub

End Class

用法：

Me.TextBox1.Text = String.Join(Environment.NewLine, Permutation.Create({"c"c, "f"c, "a"c, "m"c}, sort:=False))

输出：

cfam
cfma
cafm
camf
cmfa
cmaf
fcam
fcma
facm
famc
fmca
fmac
acfm
acmf
afcm
afmc
amcf
amfc
mcfa
mcaf
mfca
mfac
macf
mafc

该类基于以下链接中的
C++
代码：

这是你的家庭作业吗？我的论文很准确，我只是要求提供伪代码，因为如果不先了解算法回溯中的工作原理，我仍然无法理解如何编写代码；）
cfam
cfma
cafm
camf
cmfa
cmaf
fcam
fcma
facm
famc
fmca
fmac
acfm
acmf
afcm
afmc
amcf
amfc
mcfa
mcaf
mfca
mfac
macf
mafc