适应组合代码大列表

Question

我有以下代码来生成一个小列表的字符串的组合，并希望适应这个超过300个字符串words.Can任何人都可以建议如何改变此代码或使用一种不同的方法。

Public Class combinations 



Public Shared Sub main() 

    Dim myAnimals As String = "cat dog horse ape hen mouse" 

    Dim myAnimalCombinations As String() = BuildCombinations(myAnimals) 

    For Each combination As String In myAnimalCombinations 
     ''//Look on the Output Tab for the results! 
     Console.WriteLine("(" & combination & ")") 
    Next combination 

    Console.ReadLine() 

End Sub 



Public Shared Function BuildCombinations(ByVal inputString As String) As String() 

    ''//Separate the sentence into useable words. 
    Dim wordsArray As String() = inputString.Split(" ".ToCharArray) 

    ''//A plase to store the results as we build them 
    Dim returnArray() As String = New String() {""} 

    ''//The 'combination level' that we're up to 
    Dim wordDistance As Integer = 1 

    ''//Go through all the combination levels... 
    For wordDistance = 1 To wordsArray.GetUpperBound(0) 

     ''//Go through all the words at this combination level... 
     For wordIndex As Integer = 0 To wordsArray.GetUpperBound(0) - wordDistance 

      ''//Get the first word of this combination level 
      Dim combination As New System.Text.StringBuilder(wordsArray(wordIndex)) 

      ''//And all all the remaining words a this combination level 
      For combinationIndex As Integer = 1 To wordDistance 

       combination.Append(" " & wordsArray(wordIndex + combinationIndex)) 

      Next combinationIndex 

      ''//Add this combination to the results 
      returnArray(returnArray.GetUpperBound(0)) = combination.ToString 

      ''//Add a new row to the results, ready for the next combination 
      ReDim Preserve returnArray(returnArray.GetUpperBound(0) + 1) 

     Next wordIndex 

    Next wordDistance 

    ''//Get rid of the last, blank row. 
    ReDim Preserve returnArray(returnArray.GetUpperBound(0) - 1) 

    ''//Return combinations to the calling method. 
    Return returnArray 

End Function 

End Class 

'

CHANGES //

对于wordDistance = 1要在代码inputList.Count.ToString/2

 Dim count = inputList.Count.ToString 

     'Go through all the words at this combination level... 
     For wordIndex As Integer = 0 To inputList.Count.ToString - wordDistance 

      'Get the first word of this combination level 
      combination.Add(inputList.Item(wordIndex)) 
      'And all all the remaining words a this combination level 
      For combinationIndex As Integer = 1 To wordDistance 
       combination.Add(" " & inputList.Item(wordIndex + combinationIndex)) 
      Next combinationIndex 

      'Add this combination to the results 

      If Not wordsList.Contains(combination) Then 
       wordsList.Add(combination.ToString) 
      End If 

      'Add a new row to the results, ready for the next combination 
      'ReDim Preserve returnArray(returnArray.GetUpperBound(0) + 1) 

     Next wordIndex 

    Next wordDistance 

Answer 1

一个明显的一点是使用ReDim的使用保留。这可能是一个相当缓慢的操作，因为我认为每次大小改变时它会将整个数组复制到一个新数组中，并且由于您在循环内执行此操作，因此我认为这可能是一个重大问题。

解决这个问题的最简单方法是停止使用这些类型的数组，而是使用List和它的Add方法。

Answer 2

我想确保我明白你想要先做什么。你的问题似乎是：

• 给出一个字符串列表，
• 返回从列表n个项目每个可能的组合，
• 其中n = 2至清单

的长度例如，在5个字符串的列表中，您需要2个字符串，3个字符串，4个字符串和5个字符串的所有组合。

如果这是您的问题的准确陈述，有一个明显的问题需要指出。您将生成的项目数量为2 ^（列表长度）。这意味着试图生成300个项目的所有组合将永远不会很快，无论如何。此外，除了最小的列表之外，您将需要懒懒地生成项目，否则将耗尽内存。

如果你不想要所有长度的所有组合，你可能想澄清你的问题，以更好地表达你想要的目标。