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Greycoat21's solution

to Nth Prime in the Delphi Pascal Track

Published at Mar 15 2020 · 0 comments
Instructions
Test suite
Solution

Given a number n, determine what the nth prime is.

By listing the first six prime numbers: 2, 3, 5, 7, 11, and 13, we can see that the 6th prime is 13.

If your language provides methods in the standard library to deal with prime numbers, pretend they don't exist and implement them yourself.

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

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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

A variation on Problem 7 at Project Euler http://projecteuler.net/problem=7

Submitting Incomplete Solutions

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

uNthPrimeTests.pas

unit uNthPrimeTests;

interface

uses
  DUnitX.TestFramework;

const
  CanonicalVersion = '2.1.0.1';

type
  [TestFixture]
  TNthPrimeTest = class(TObject) 
  public
    [Test]
//    [Ignore('Comment the "[Ignore]" statement to run the test')]
    procedure there_is_no_zeroth_prime;

    [Test]
    [Ignore]
    procedure first_prime;

    [Test]
    [Ignore]
    procedure second_prime;

    [Test]
    [Ignore]
    procedure sixth_prime;

    [Test]
    [Ignore]
    procedure big_prime;
  end;

implementation

uses
  System.SysUtils, uNthPrime;


procedure TNthPrimeTest.first_prime;
begin
  Assert.AreEqual(2, NthPrime(1));
end;

procedure TNthPrimeTest.second_prime;
begin
  Assert.AreEqual(3, NthPrime(2));
end;

procedure TNthPrimeTest.sixth_prime;
begin
  Assert.AreEqual(13, NthPrime(6));
end;

procedure TNthPrimeTest.big_prime;
begin
  Assert.AreEqual(104743, NthPrime(10001));
end;

procedure TNthPrimeTest.there_is_no_zeroth_prime;
begin
  Assert.WillRaiseWithMessage(procedure begin NthPrime(0); end , EArgumentOutOfRangeException, 'there is no zeroth prime');
end;

initialization
  TDUnitX.RegisterTestFixture(TNthPrimeTest);
end.
unit uNthPrime;

interface

function NthPrime(N: Integer): Integer;

implementation

uses
  SysUtils;

function IsPrime(Int: Integer): Boolean;
var
  i: Integer;
begin
  Result := True;
  for i := 2 to Int - 1 do begin
    if Int mod i = 0 then begin
      Exit(False);
    end;
  end;
end;

function NthPrime(N: Integer): Integer;
var
  i, PrimeCount: Integer;
begin
  if N < 1 then
    raise EArgumentOutOfRangeException.Create('there is no zeroth prime');

  i := 1; // *The first prime is 2
  PrimeCount := 0;
  repeat

    Inc(i); // *

    if IsPrime(i) then
      Inc(PrimeCount);

  until PrimeCount = N;

  Result := i;
end;

end.

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