列出VB.NET中的所有組合

Question

在VB.NET中，如何列出列表中的所有可能組合。我希望能夠使用傳遞參數的方法來指定每個組合中的項目數。在我的情況下，我只想要2.我不想以不同的順序看到相同的組合。我想將這些信息記錄在列表框中。我嘗試了其他帖子的要求，但他們似乎不適合我。

感謝您的任何幫助

Answer 1

這是一個快速和骯髒的方式做到這一點。這是非常低效的，絕不是「最好」的方式。一旦代碼「停止」，uniqueResults將包含要添加到列表框中的項目。

Module Module1 

    Sub Main() 
     Dim source As New List(Of String)({"cat", "dog", "hamster", "goat"}) 
     Dim results As List(Of List(Of String)) = Combine(source, 3) 
     Dim uniqueResults As List(Of String) = Filter(results) 
     stop 
    End Sub 

    ''' <summary> 
    ''' Builds an N length list of all possible combinations of Source 
    ''' </summary> 
    ''' <param name="source">a list of strings containing the possible items</param> 
    ''' <param name="length">the length of the list of items to return</param> 
    Private Function Combine(source As List(Of String), length As Integer) As List(Of List(Of String)) 
     Dim ret As New List(Of List(Of String)) 
     Combine(source, length, New List(Of String), ret) 
     Return ret 
    End Function 

    ''' <summary> 
    ''' Recursivly builds an N length list of all possible combinations of Source 
    ''' </summary> 
    ''' <param name="source">a list of strings containing the possible items</param> 
    ''' <param name="length">the number of items remaining to add to the list</param> 
    ''' <param name="value">the current list being built</param> 
    ''' <param name="output">a list of all possible combinations</param> 
    Private Sub Combine(source As List(Of String), length As Integer, value As List(Of String), output As List(Of List(Of String))) 
     For i As Integer = 0 To source.Count - 1 
      value.Add(source(i)) 
      If length <= 1 Then 
       'Console.WriteLine(String.Join(", ", value)) 
       output.Add(New List(Of String)(value)) 
      Else 
       Combine(source, length - 1, value, output) 
      End If 
      value.RemoveAt(value.Count - 1) 
     Next 
    End Sub 

    ''' <summary> 
    ''' returns only unique patterns 
    ''' </summary> 
    ''' <param name="list"></param> 
    ''' <returns></returns> 
    ''' <remarks></remarks> 
    Private Function Filter(list As List(Of List(Of String))) As List(Of String) 
     Dim found As New HashSet(Of String) 

     For Each item As List(Of String) In list 
      Dim temp As New List(Of String)(item) 
      temp.Sort() 
      Dim s As String = String.Join(", ", temp) 
      If Not found.Contains(s) Then 
       found.Add(s) 
      End If 
     Next 
     Return New List(Of String)(found) 
    End Function 

End Module