Question

我有这段代码：

        Dim combinations As New List(Of String)

        Dim word As String = "abc"

        For c1 = 0 To word.Length - 1
            combinations.Add(word(c1))
            For c2 = 0 To word.Length - 1
                If c2 <> c1 Then
                    combinations.Add(word(c1) & word(c2))
                    For c3 = 0 To word.Length - 1
                        If c3 <> c2 And c3 <> c1 Then
                            combinations.Add(word(c1) & word(c2) & word(c3))
                        End If
                    Next
                End If
            Next
        Next

输出：

a, ab, abc, ac, acb, b, ba, bac, bc, bca, c, ca, cab, cb, cba

如何创建一个函数，它可以为无限的字长做同样的事情？

Answer 1

Backtracking是一种很好的方法。基本上，您可以随时构建各种输入的图表，添加下一个可用的输出，直到用完为止，然后备份并删除一个，并将其替换为另一个。这是another explanation。

Answer 2

我不是vb.net编码器，但看到这是一个有趣的练习。这是我在伪代码中的答案：

array A = ('a','b','c') //add all the unique letters to an array
integer COUNT = length of A
array P = A //initialize P (the final answer) as A
array L = A //initialize L as A to start
for j=2 to COUNT {
  array N = () //new empty array
  foreach i in L { //loop through all the elements of L
     foreach m in A { //loop through all the elements of A
        if (i does not contain m) { 
          push (i + m) into P //push the concatenation of i & m into array P
          push (i + m) into N //do the same thing for array N the next loop through
        }  
     }
  }
  L = N 
}
change P to a string or whatever you want the output to be....

获得所有组合而不重复

2 个答案: