Data update

Task/Knuths-algorithm-S/FreeBASIC/knuths-algorithm-s.basic

@@ -0,0 +1,98 @@
+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