Imports System
Module Program
''' <summary>
''' Returns K unique random elements from the specified array.
'''
''' <param name="source">
''' The source array. Its size is determined at runtime and does not
''' need to be known at compile time.
''' </param>
''' <param name="k">
''' Number of random elements to retrieve.
''' </param>
''' <returns>
''' An array containing K unique randomly selected elements.
''' </returns>
'''
''' Explanation:
''' ----------------------------
''' This function uses a partial Fisher-Yates shuffle:
'''
''' 1. Copy the source array so the original remains unchanged.
''' 2. Perform only the first K shuffle iterations.
''' 3. After each iteration, one random element is moved into
''' its final sampled position.
''' 4. The first K elements of the shuffled copy form the sample.
'''
''' Advantages:
''' - No duplicate selections.
''' - Uniform random distribution.
''' - Preserves the original array.
''' - Efficient when K is smaller than the array length.
''' ----------------------------
Function GetRandomSample(
source As Integer(),
k As Integer) As Integer()
If source Is Nothing Then
Throw New ArgumentNullException(NameOf(source))
End If
If k < 0 OrElse k > source.Length Then
Throw New ArgumentOutOfRangeException(
NameOf(k),
"K must be between 0 and the number of elements.")
End If
' Create a copy so the source array is not modified.
Dim workingCopy As Integer() =
CType(source.Clone(), Integer())
Dim rng As New Random()
' Partial Fisher-Yates shuffle.
For i As Integer = 0 To k - 1
Dim randomIndex As Integer =
rng.Next(i, workingCopy.Length)
Dim temp As Integer = workingCopy(i)
workingCopy(i) = workingCopy(randomIndex)
workingCopy(randomIndex) = temp
Next
' Copy the first K sampled elements.
Dim result(k - 1) As Integer
Array.Copy(
workingCopy,
0,
result,
0,
k)
Return result
End Function
Sub Main()
Try
' Array size is only known at runtime.
Dim numbers() As Integer =
{
10, 20, 30, 40, 50,
60, 70, 80, 90, 100
}
Dim k As Integer = 4
Dim sample() As Integer =
GetRandomSample(numbers, k)
Console.WriteLine("Original Array:")
Console.WriteLine(String.Join(", ", numbers))
Console.WriteLine()
Console.WriteLine($"Random Sample ({k} elements):")
Console.WriteLine(String.Join(", ", sample))
Catch ex As Exception
Console.WriteLine($"Error: {ex.Message}")
End Try
End Sub
End Module
'
' run:
'
' Original Array:
' 10, 20, 30, 40, 50, 60, 70, 80, 90, 100
'
' Random Sample (4 elements):
' 50, 40, 80, 30
'
'
