🎉 Exercism Research is now launched. Help Exercism, help science and have some fun at research.exercism.io 🎉
Avatar of Neftali

Neftali's solution

to Prime Factors in the Delphi Pascal Track

Published at Jan 21 2020 · 0 comments
Instructions
Test suite
Solution

Compute the prime factors of a given natural number.

A prime number is only evenly divisible by itself and 1.

Note that 1 is not a prime number.

Example

What are the prime factors of 60?

  • Our first divisor is 2. 2 goes into 60, leaving 30.
  • 2 goes into 30, leaving 15.
    • 2 doesn't go cleanly into 15. So let's move on to our next divisor, 3.
  • 3 goes cleanly into 15, leaving 5.
    • 3 does not go cleanly into 5. The next possible factor is 4.
    • 4 does not go cleanly into 5. The next possible factor is 5.
  • 5 does go cleanly into 5.
  • We're left only with 1, so now, we're done.

Our successful divisors in that computation represent the list of prime factors of 60: 2, 2, 3, and 5.

You can check this yourself:

  • 2 * 2 * 3 * 5
  • = 4 * 15
  • = 60
  • Success!

Testing

In order to run the tests for this track, you will need to install DUnitX. Please see the installation instructions for more information.

Loading Exercises into Delphi

If Delphi is properly installed, and *.dpr file types have been associated with Delphi, then double clicking the supplied *.dpr file will start Delphi and load the exercise/project. control + F9 is the keyboard shortcut to compile the project or pressing F9 will compile and run the project.

Alternatively you may opt to start Delphi and load your project via. the File drop down menu.

When Questions Come Up

We monitor the Pascal-Delphi support room on gitter.im to help you with any questions that might arise.

Submitting Exercises

Note that, when trying to submit an exercise, make sure the exercise file you're submitting is in the exercism/delphi/<exerciseName> directory.

For example, if you're submitting ubob.pas for the Bob exercise, the submit command would be something like exercism submit <path_to_exercism_dir>/delphi/bob/ubob.pas.

Source

The Prime Factors Kata by Uncle Bob http://butunclebob.com/ArticleS.UncleBob.ThePrimeFactorsKata

Submitting Incomplete Solutions

It's possible to submit an incomplete solution so you may request help from a mentor.

uPrimeFactorsTests.pas

unit uPrimeFactorsTests;

interface
uses
  DUnitX.TestFramework;
  
const
  CanonicalVersion = '1.1.0.1';

type
  [TestFixture]
  TPrimeFactorsTest = class(TObject)
  private
    procedure CompareArrays(Array1, Array2: TArray<Int64>);
  public
    [Test]
//    [Ignore('Comment the "[Ignore]" statement to run the test')]
    procedure no_factors;

    [Test]
    [Ignore]
    procedure prime_number;

    [Test]
    [Ignore]
    procedure square_of_a_prime;

    [Test]
    [Ignore]
    procedure cube_of_a_prime;

    [Test]
    [Ignore]
    procedure product_of_primes_and_non_primes;

    [Test]
    [Ignore]
    procedure product_of_primes;

    [Test]
    [Ignore]
    procedure factors_include_a_large_prime;
  end;

implementation

uses
  System.SysUtils, uPrimeFactors;

procedure TPrimeFactorsTest.CompareArrays(Array1, Array2: TArray<Int64>);
var
  i: integer;
begin
  Assert.AreEqual(Length(Array1), Length(Array2), ' - Array lengths must be equal');
  for i := Low(Array1) to High(Array1) do
    Assert.AreEqual(Array1[i], Array2[i], format('Expecting element %d to = %d, Actual = %d',
      [i, Array1[i], Array2[i]]));
end;

procedure TPrimeFactorsTest.cube_of_a_prime;
begin
  CompareArrays([2, 2, 2], TPrimeFactors.factors(8));
end;

procedure TPrimeFactorsTest.factors_include_a_large_prime;
begin
  CompareArrays([11, 9539, 894119], TPrimeFactors.factors(93819012551));
end;

procedure TPrimeFactorsTest.no_factors;
begin

  CompareArrays([], TPrimeFactors.factors(1));
end;

procedure TPrimeFactorsTest.prime_number;
begin
  CompareArrays([2], TPrimeFactors.factors(2));
end;

procedure TPrimeFactorsTest.product_of_primes;
begin
  CompareArrays([5, 17, 23, 461], TPrimeFactors.factors(901255));
end;

procedure TPrimeFactorsTest.product_of_primes_and_non_primes;
begin
  CompareArrays([2, 2, 3], TPrimeFactors.factors(12));
end;

procedure TPrimeFactorsTest.square_of_a_prime;
begin
  CompareArrays([3, 3], TPrimeFactors.factors(9));
end;

initialization
  TDUnitX.RegisterTestFixture(TPrimeFactorsTest);
end.
unit uPrimeFactors;

interface

type
  TPrimeFactors = class
    class function Factors(AValue:Int64): TArray<Int64>;
  end;

implementation

uses
  System.SysUtils, System.Generics.Collections;

{ TPrimeFactors }

class function TPrimeFactors.Factors(AValue: Int64): TArray<Int64>;
var
  l:TList<Int64>;
  i:Int64;
begin
  Result := [];
  l := TList<Int64>.Create;
  try
    while (AValue <> 1) do begin
      for i := 2 to AValue do begin
        if ((AValue mod i) = 0)  then begin
          l.Add(i);
          Break;    // not continue if founded
        end;
      end;
      AValue := AValue div i;
    end;
    Result := l.ToArray;
  finally
    FreeAndNil(l);
  end;
end;

end.

Community comments

Find this solution interesting? Ask the author a question to learn more.

What can you learn from this solution?

A huge amount can be learned from reading other people’s code. This is why we wanted to give exercism users the option of making their solutions public.

Here are some questions to help you reflect on this solution and learn the most from it.

  • What compromises have been made?
  • Are there new concepts here that you could read more about to improve your understanding?