Type SampleState
	sample(0 To 99) As Integer ' Array to store the sample (arbitrary maximum size)
	sampleSize As Integer ' Current sample size
	i As Integer ' Counter of processed elements
	n As Integer ' Desired sample size
End Type

' Function to generate a random number between 0 and max-1
Function randInt(Byval max As Integer) As Integer
    Return Int(Rnd() * max)
End Function

' Function to create a new sampler
Function createSampler(Byval n As Integer) As SampleState
    Dim sampler As SampleState
    sampler.sampleSize = 0
    sampler.i = 0
    sampler.n = n
    Return sampler
End Function

' Function to process a new element and update the sample
Function sampleOfN(Byref sampler As SampleState, Byval item As Integer) As Integer Ptr
    sampler.i += 1

    If sampler.i <= sampler.n Then
        sampler.sample(sampler.sampleSize) = item
        sampler.sampleSize += 1
    Else
        If randInt(sampler.i) < sampler.n Then
            sampler.sample(randInt(sampler.n)) = item
        End If
    End If

    Return @sampler.sample(0)
End Function

Sub printArray(arr() As Integer, Byval size As Integer)
    Print "["
    For i As Integer = 0 To size-1
        Print arr(i)
        If i < size-1 Then Print ", "
    Next
    Print "]"
End Sub

Sub main()
    Dim As Integer i, j

    Dim As Integer frequency(0 To 9)
    For i = 0 To 9
        frequency(i) = 0
    Next

    Print "Single run samples for n = 3:"

    Dim As SampleState sampler = createSampler(3)
    Dim As Integer Ptr samplePtr
    Dim As Integer sample(0 To 2)

    For i = 0 To 9
        samplePtr = sampleOfN(sampler, i)

        For j = 0 To sampler.sampleSize-1
            sample(j) = samplePtr[j]
        Next

        Print "  Item: " & i & " -> sample: ";
        Print "[ ";
        For j = 0 To sampler.sampleSize-1
            Print Chr(8) & sample(j);
            If j < sampler.sampleSize-1 Then Print ",  ";
        Next
        Print "]"
    Next

    For i = 0 To 99999
        sampler = createSampler(3)

        For j = 0 To 9
            samplePtr = sampleOfN(sampler, j)
        Next

        For j = 0 To sampler.n-1
            frequency(samplePtr[j]) += 1
        Next
    Next

    Print !"\nTest item frequencies for 100000 runs:"
    For i = 0 To 9
        Print "  " & i & ": " & frequency(i)
    Next
End Sub

Randomize Timer
main()

Sleep