tasks a-s

Task/Permutations-Derangements/Ada/permutations-derangements.ada

@@ -0,0 +1,54 @@
+with Ada.Text_IO; use Ada.Text_IO;
+procedure DePermute is
+   type U64 is mod 2**64;
+   type Num is range 0 .. 20;
+   type NumList is array (Natural range <>) of Num;
+   type PtNumList is access all NumList;
+   package IO is new Ada.Text_IO.Integer_IO (Num);
+   package UIO is new Ada.Text_IO.Modular_IO (U64);
+
+   function deranged (depth : Natural; list : PtNumList;
+      show : Boolean) return U64 is
+      tmp : Num;  count : U64 := 0;
+   begin
+      if depth = list'Length then
+         if show then
+            for i in list'Range loop IO.Put (list (i), 2); end loop;
+            New_Line;
+         end if;  return 1;
+      end if;
+      for i in reverse depth .. list'Last loop
+         if Num (i + 1) /= list (depth) then
+            tmp := list (i); list (i) := list (depth); list (depth) := tmp;
+            count := count + deranged (depth + 1, list, show);
+            tmp := list (i); list (i) := list (depth); list (depth) := tmp;
+         end if;
+      end loop;
+      return count;
+   end deranged;
+
+   function gen_n (len : Natural; show : Boolean) return U64 is
+      list : PtNumList;
+   begin
+      list := new NumList (0 .. len - 1);
+      for i in list'Range loop list (i) := Num (i + 1); end loop;
+      return deranged (0, list, show);
+   end gen_n;
+
+   function sub_fact (n : Natural) return U64 is begin
+      if n < 2 then return U64 (1 - n);
+      else return (sub_fact (n - 1) + sub_fact (n - 2)) * U64 (n - 1);
+      end if;
+   end sub_fact;
+
+   count : U64;
+begin
+   Put_Line ("Deranged 4:");
+   count := gen_n (4, True);
+   Put_Line ("List vs. calc:");
+   for i in Natural range 0 .. 9 loop
+      IO.Put (Num (i), 1);  UIO.Put (gen_n (i, False), 7);
+      UIO.Put (sub_fact (i), 7);  New_Line;
+   end loop;
+   Put_Line ("!20 = " & U64'Image (sub_fact (20)));
+end DePermute;