VB.NET 排列组合算法实现

 假设给定数组 A[ ] ， A中元素不重复，要求出所有元素的组合：
A[a, b, c]
→ a
→ b
→ c
→ a b
→ a c
→ b c
→ a b c
' 求给定数组，n个元素进行组合的枚举结果。
' n=1时，组合个数为1，如：a；
' n=2时，组合个数为2，如：ab；
' n=3时，组合个数为3，如：abc；
Function Comb(ByVal arr As List(Of String), ByVal n As Integer) As List(Of String)
Dim newArray As List(Of String) = New List(Of String)
If n = 1 Then
newArray = arr
ElseIf n = 2 Then
For i As Integer = 0 To arr.Count - 1
For j As Integer = i + 1 To arr.Count - 1
newArray.Add(arr(i) & "&" & arr(j))
Next
Next
Else
Dim str As String = ""
For i As Integer = 0 To arr.Count - 1
str = arr(i)
Dim tempArr As List(Of String) = New List(Of String)
For j As Integer = i + 1 To arr.Count - 1

tempArr.Add(arr(j))
Next
If tempArr.Count < n - 1 Then

Exit For
End If
Dim arr1 As List(Of String) = Comb(tempArr, n - 1)
For Each strTemp As String In arr1
newArray.Add(str & "&" & strTemp)
Next
Next
End If
Return newArray
End Function使用：
Sub Main()
'使用例：
'构造一个数组：
Dim arrList As List(Of String) = New List(Of String) From {"a", "b", "c"}
For i As Integer = 1 To arrList.Count
Dim lstResult As List(Of String) = Comb(arrList, i)
For Each str As String In lstResult
Console.WriteLine(str)
Next
Next
Console.Read()
End Sub
数组："a", "b", "c", "d"输出结果：
a
b
c
d
a&b
a&c
a&d
b&c
b&d
c&d
a&b&c
a&b&d
a&c&d
b&c&d
a&b&c&d
 C# 版本的：
public static IEnumerable<string> Comb(string chars)
{
var data = chars.ToCharArray();
var result = new[] {""};
for(var i=0; i<chars.Length; i++)
{
result = (from a in data
from b in result
where !b.Contains(a)
select a + "" + b).ToArray();
}
return result;
}输入： abcd
输出：
abc
acb
bac
bca
cab
cba