求N个字符的组合算法
RT.
有M个字符,求Cm1+Cm2+Cm3+...+Cmm的所有可能的组合字符串(不分顺序).

[解决办法]
imports Microsoft.VisualBasic
imports System

public module MyModule
private s as string = "abc "
private m as integer = s.Length
private b(m-1) as boolean
sub Main
Combine(0)
end sub
sub Combine(byval i as integer)
if i=m then
Output()
else
b(i) = false
Combine(i+1)
b(i) = true
Combine(i+1)
end if
end sub
sub Output()
dim sb as new System.Text.StringBuilder
for i as integer= 0 to m-1
if b(i) then sb.Append(s.Chars(i))
next
Console.WriteLine(sb.ToString())
end sub
end module