Avatar of freddie2025

freddie2025's solution

to Prime Factors in the JavaScript Track

Published at Apr 14 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!

Setup

Go through the setup instructions for Javascript to install the necessary dependencies:

https://exercism.io/tracks/javascript/installation

Requirements

Install assignment dependencies:

$ npm install

Making the test suite pass

Execute the tests with:

$ npm test

In the test suites all tests but the first have been skipped.

Once you get a test passing, you can enable the next one by changing xtest to test.

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 can see how others have completed the exercise.

prime-factors.spec.js

import { primeFactors } from './prime-factors';

describe('primeFactors', () => {
  test('returns an empty array for 1', () => expect(primeFactors(1)).toEqual([]));

  xtest('factors 2', () => expect(primeFactors(2)).toEqual([2]));

  xtest('factors 3', () => expect(primeFactors(3)).toEqual([3]));

  xtest('factors 4', () => expect(primeFactors(4)).toEqual([2, 2]));

  xtest('factors 6', () => expect(primeFactors(6)).toEqual([2, 3]));

  xtest('factors 8', () => expect(primeFactors(8)).toEqual([2, 2, 2]));

  xtest('factors 9', () => expect(primeFactors(9)).toEqual([3, 3]));

  xtest('factors 27', () => expect(primeFactors(27)).toEqual([3, 3, 3]));

  xtest('factors 625', () => expect(primeFactors(625)).toEqual([5, 5, 5, 5]));

  xtest('factors 901255', () => expect(primeFactors(901255)).toEqual([5, 17, 23, 461]));

  xtest('factors 93819012551', () => expect(primeFactors(93819012551)).toEqual([11, 9539, 894119]));
});
//
// This is only a SKELETON file for the 'Prime Factors' exercise. It's been provided as a
// convenience to get you started writing code faster.
//

export const primeFactors = (number) => {
  let list = [];
  let division = 2;

  do
  {
      if(number % division == 0)
      {
          list.push(division);
          number = number / division;
          division = 2; 
      } 
      else division++;                
  } 
  while (number > 1);

  return list;
};

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?