得到重复的组合

问题描述

| 如何将所有可能的组合写入控制台？例如，如果用户输入abc，则它将写入aaa，aab，aac，abb，abc，acc，acc，bbb，bbc，ccc。请帮我。 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

在虚线后必须执行某些操作以删除不必要的排列，从而仅保留有效的组合。     

解决方法

您可以使用附加参数abcIndex将用于abc（i）或右侧的字母限制为字母，然后从此处开始for循环。只写字母按字母顺序排列的字符串，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

致电：

outputStrings(\"\",3,0)

    ,

def go(chars,thusfar):
    if len(thusfar) = len(chars):
        print thusfar
    for char in chars:
        go(chars,thusfar+char);

这应该足够容易地转换为VB（阅读：我不知道VB）     ,您只需要在那里进行递归调用。

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.Count - 1
        Dim temp As String = startString           
        temp += abc(i)
        If temp.Length = letterCount Then
            Console.WriteLine(temp)
        Else
            outputStrings(temp,letterCount)
        End If

    Next
End Sub

请注意，如果有人输入负数，则您的代码将永远运行。我将通过简单的练习来解决该问题。     ,来自这里的惊人代码：

Private Shared Function PermutationsWithRepetition(Of T)(list As IEnumerable(Of T),length As Integer) As IEnumerable(Of IEnumerable(Of T))
        If length = 1 Then
            Return list.[Select](Function(x) New T() {x})
        End If
        Return PermutationsWithRepetition(list,length - 1).SelectMany(Function(x) list,Function(t1,t2) t1.Concat(New T() {t2}))
    End Function

可以与Integer，Char，Double等一起使用。 使用示例：

Dim myarray(1) As Integer
myarray(0) = 1
myarray(1) = 2
Dim k As Integer = 2 \'number of \"slots\" to do the permutations

mypermutations = PermutationsWithRepetition(myarray,k)

For Each row As IEnumerable(Of Integer) In mypermutations
            Console.WriteLine(\"\")
            For Each col As IntegerIn row
                Console.Write(col.toString())
            Next            
Next

输出： 11 12 21 22