Possible Selections With Repetition.
Imagine being given the opportunity to pick six (6) exercise books
from a book-shop having 10 different brands of exercise books -
Ben 10, Chelsea F.C., Superman, Tottenham F.C.,
Indomitables, Manchester City F.C., Spider Man,
Power Rangers, Liverpool F.C. and Bat Man exercise books.
If you happen to be a big Power Rangers fan, nothing stops you from
selecting all 6 exercise books to be Power Rangers exercise books.
But you can as well decide to pick only 3 Power Rangers exercise books
and make up for the other 3 with any other brands of exercise book.
Code for Repetitive Selection in VB.Net
The algorithm for Selection with Repetition will be a lot similar to that of combination.
- Beginning with the first member in the mother set, match it separately with every member - including itself - until the required Selection group-size (r) is reached.
- When every possible Selection with this member is exhausted, move to the next member in the mother set and repeat Step I.
This is how our Repetitive Selection code in VB.Net will work.
Create a new VB.Net class file; Call it Selection
.
Optionally, Create a new VB.Net module file; Call it Miscellaneous_Selection
.
Type out the adjoining VB.Net algorithm for Selection with Repetition.
VB.Net Code for Selection Class
Public words As String()
Public r As Integer ' min length Of word
Protected complete_group As List(Of String())
Private i As Integer
Public Function groupSelection(candidates As String(), size As Integer) As List(Of String())
words = candidates
r = size
complete_group = New List(Of String())
i = 0
recursiveFillUp(New List(Of String))
Return complete_group
End Function
' pick elements recursively
Protected Sub recursiveFillUp(temp As List(Of String))
Dim picked_elements(words.Length) As List(Of String)
Dim j As Integer = i
Do While j < words.Length
picked_elements(j) = New List(Of String)
picked_elements(j).AddRange(temp)
picked_elements(j).Add(words(j))
' recoil factor
If i >= words.Length Then
i = j
End If
' satisfied yet?
If picked_elements(j).Count = r Then
complete_group.Add(picked_elements(j).ToArray())
ElseIf picked_elements(j).Count < r Then
recursiveFillUp(picked_elements(j))
End If
j += 1
Loop
j -= 1
If picked_elements(j).Equals(Nothing) = False And picked_elements(j).Count = r Then
i += 1 ' keep recoil factor straightened out
End If
End Sub
End Class
Miscellaneous_Selection Module
Sub Main()
Dim goods As String() = {"0", "1", "2", "3", "4", "5", "6", "7", "8", "9"}
Dim pick As New Selection
Dim result As List(Of String()) = pick.groupSelection(goods, 2)
' print choices and operation
Console.Write("[ ")
For Each choice As String In pick.words
Console.Write(choice & "; ")
Next
Console.WriteLine("] selection " & pick.r & ":" & Environment.NewLine)
' print out selections nicely
Dim i As Integer = 0
For Each group As String() In result
i += 1
Console.Write(i & ": ")
For Each member As String In group
Console.Write(member & "; ")
Next
Console.WriteLine()
Next
Console.WriteLine(Environment.NewLine & "Number of ways is " & result.Count & ".")
End Sub
End Module