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Hofstadter Figure-Figure sequences: Difference between revisions
Hofstadter Figure-Figure sequences (view source)
Revision as of 12:55, 4 November 2011
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* [http://mathworld.wolfram.com/HofstadterFigure-FigureSequence.html Wolfram Mathworld]
* Wikipedia: [[wp:Hofstadter_sequence#Hofstadter_Figure-Figure_sequences|Hofstadter Figure-Figure sequences]].
=={{header|Ada}}==
Specifying a package providing the functions FFR and FFS:
<lang Ada>package Hofstadter_Figure_Figure is
function FFR(P: Positive) return Positive;
function FFS(P: Positive) return Positive;
end Hofstadter_Figure_Figure;</lang>
The implementation of the package internally uses functions which generate an array of Figures or Spaces:
<lang Ada>package body Hofstadter_Figure_Figure is
type Positive_Array is array (Positive range <>) of Positive;
function FFR(P: Positive) return Positive_Array is
Figures: Positive_Array(1 .. P+1);
Space: Positive := 2;
Space_Index: Positive := 2;
begin
Figures(1) := 1;
for I in 2 .. P loop
Figures(I) := Figures(I-1) + Space;
Space := Space+1;
while Space = Figures(Space_Index) loop
Space := Space + 1;
Space_Index := Space_Index + 1;
end loop;
end loop;
return Figures(1 .. P);
end FFR;
function FFR(P: Positive) return Positive is
Figures: Positive_Array(1 .. P) := FFR(P);
begin
return Figures(P);
end FFR;
function FFS(P: Positive) return Positive_Array is
Spaces: Positive_Array(1 .. P);
Figures: Positive_Array := FFR(P+1);
J: Positive := 1;
K: Positive := 1;
begin
for I in Spaces'Range loop
while J = Figures(K) loop
J := J + 1;
K := K + 1;
end loop;
Spaces(I) := J;
J := J + 1;
end loop;
return Spaces;
end FFS;
function FFS(P: Positive) return Positive is
Spaces: Positive_Array := FFS(P);
begin
return Spaces(P);
end FFS;
end Hofstadter_Figure_Figure;</lang>
Finally, a test program for the package, solving the task at hand:
<lang Ada>with Ada.Text_IO, Hofstadter_Figure_Figure;
procedure Test_HSS is
use Hofstadter_Figure_Figure;
A: array(1 .. 1000) of Boolean := (others => False);
J: Positive;
begin
for I in 1 .. 10 loop
Ada.Text_IO.Put(Integer'Image(FFR(I)));
end loop;
Ada.Text_IO.New_Line;
for I in 1 .. 40 loop
J := FFR(I);
if A(J) then
raise Program_Error with Positive'Image(J) & " used twice";
end if;
A(J) := True;
end loop;
for I in 1 .. 960 loop
J := FFS(I);
if A(J) then
raise Program_Error with Positive'Image(J) & " used twice";
end if;
A(J) := True;
end loop;
for I in A'Range loop
if not A(I) then raise Program_Error with Positive'Image(I) & " unused";
end if;
end loop;
Ada.Text_IO.Put_Line("Test Passed: No overlap between FFR(I) and FFS(J)");
exception
when Program_Error => Ada.Text_IO.Put_Line("Test Failed"); raise;
end Test_HSS;</lang>
The output of the test program:
<lang> 1 3 7 12 18 26 35 45 56 69
Test Passed: No overlap between FFR(I) and FFS(J)</lang>
=={{header|Common Lisp}}==
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