Initial data commit

Task/Knuths-algorithm-S/Ada/knuths-algorithm-s-2.ada

@@ -0,0 +1,38 @@
+with Ada.Numerics.Float_Random, Ada.Numerics.Discrete_Random;
+
+package body S_Of_N_Creator is
+
+   package F_Rnd renames Ada.Numerics.Float_Random;
+   F_Gen: F_Rnd.Generator;
+
+   package D_Rnd is new Ada.Numerics.Discrete_Random(Index_Type);
+   D_Gen: D_Rnd.Generator;
+
+   Item_Count: Natural := 0; -- this is a global counter
+   Sample: Item_Array; -- also used globally
+
+   procedure Update(New_Item: Item_Type) is
+   begin
+      Item_Count := Item_Count + 1;
+      if Item_Count <= Sample_Size then
+         -- select the first Sample_Size items as the sample
+         Sample(Item_Count) := New_Item;
+      else
+         -- for I-th item, I > Sample_Size: Sample_Size/I chance of keeping it
+         if (Float(Sample_Size)/Float(Item_Count)) > F_Rnd.Random(F_Gen)  then
+            -- randomly (1/Sample_Size) replace one of the items of the sample
+            Sample(D_Rnd.Random(D_Gen)) := New_Item;
+         end if;
+      end if;
+   end Update;
+
+   function Result return Item_Array is
+   begin
+      Item_Count := 0; -- ready to start another run
+      return Sample;
+   end Result;
+
+begin
+   D_Rnd.Reset(D_Gen); -- at package instantiation, initialize rnd-generators
+   F_Rnd.Reset(F_Gen);
+end S_Of_N_Creator;