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--
-- Project Euler problem #3
--
-- The prime factors of 13195 are 5, 7, 13 and 29.
--
-- What is the largest prime factor of the number 600851475143 ?
with Ada.Command_Line,
Ada.Containers.Vectors,
Ada.Numerics.Elementary_Functions,
Ada.Text_IO;
use Ada.Containers,
Ada.Numerics.Elementary_Functions,
Ada.Text_IO;
procedure Three is
package CL renames Ada.Command_Line;
-- For this problem, we need a 64-bit Natural subtype
subtype Long_Natural is Long_Integer range 0 .. Long_Integer'Last;
package Bucket is new Ada.Containers.Vectors (Index_Type => Natural,
Element_Type => Long_Natural);
-- Return a Vector with all the factors for `Input`
function Factors_For (Input : in Long_Natural) return Bucket.Vector is
Result : Bucket.Vector;
-- Using the "Trial Division" method detailed in this Wikipedia entry:
-- https://secure.wikimedia.org/wikipedia/en/wiki/Prime_number#Trial_division
Ceiling : constant Long_Natural := Long_Natural (Sqrt (Float (Input)));
begin
for Index in 2 .. Ceiling loop
if (Input mod Index) = 0 then
Bucket.Append (Result, Index);
end if;
end loop;
return Result;
end Factors_For;
begin
if CL.Argument_Count < 1 then
Put_Line (">>> Insufficient command line parameters!");
New_Line;
Put_Line ("Please execute with: " & CL.Command_Name & " <maxnumber>");
CL.Set_Exit_Status (CL.Failure);
return;
end if;
declare
Passed_Number : constant Long_Natural := Long_Natural'Value (CL.Argument (1));
Factors : constant Bucket.Vector := Factors_For (Passed_Number);
begin
Put_Line ("Looking for the largest prime factors for:" & Long_Natural'Image (Passed_Number));
New_Line;
for Index in 0 .. Bucket.Last_Index (Factors) loop
declare
Factor : constant Long_Natural := Bucket.Element (Factors, Index);
New_Factors : constant Bucket.Vector := Factors_For (Factor);
begin
if Bucket.Length (New_Factors) = 0 then
Put_Line (Long_Natural'Image (Factor) & " looks like a prime");
end if;
end;
end loop;
end;
end Three;
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