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