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--
-- Project Euler problem #4
--
-- A palindromic number reads the same both ways. The largest palindrome made
-- from the product of two 2-digit numbers is 9009 = 91 99.
--
-- Find the largest palindrome made from the product of two 3-digit numbers.
--
with Ada.Strings.Fixed,
Ada.Text_IO;
use Ada.Strings.Fixed,
Ada.Text_IO;
procedure Four is
Ceiling : constant Natural := 999;
function Reversed_String (Forward : in String) return String is
Result : String (Forward'Range);
begin
for Index in Result'Range loop
Result (Index) := Forward ((Forward'Length + 1) - Index);
end loop;
return Result;
end Reversed_String;
function Is_Palindrome (Input : in Natural) return Boolean is
Raw_Input_String : constant String := Natural'Image (Input);
-- Trim the leading space off the stringifyed input
Input_String : constant String := Raw_Input_String (2 .. Raw_Input_String'Last);
Length : constant Natural := Input_String'Length;
begin
if (Length mod 2) /= 0 then
return false;
end if;
declare
First_Half : constant String := Head (Input_String, (Length / 2));
Second_Half : constant String := Reversed_String (Tail (Input_String, (Length / 2)));
begin
if First_Half = Second_Half then
return true;
end if;
end;
return false;
end Is_Palindrome;
Highest_Palindrome : Natural := 0;
begin
for N in reverse 1 .. Ceiling loop
for J in reverse 1 .. Ceiling loop
declare
Product : constant Natural := J * N;
Bailout : constant Boolean := Is_Palindrome (Product);
begin
if Bailout then
if Product > Highest_Palindrome then
Highest_Palindrome := Product;
end if;
end if;
end;
end loop;
end loop;
New_Line;
Put_Line ("Highest:" & Natural'Image(Highest_Palindrome));
end Four;