PrimeFactors

prime_factors.rb

class PrimeFactors
  def self.of number
    PrimeFactors.new(number).calculate
  end
  
  def initialize number
    @number = number
    @divisor = 2
    @primes = []
  end
  
  def calculate
    return [@number] if @number <= 3
    while @number > 1
      add_prime
    end
    @primes
  end
  
  private
    def add_prime
      while @divisor <= @number do
        if evenly_divisible?
          divide_number
          push_prime_to_result
        else
          increment_divisor
        end
      end
    end
    
    def evenly_divisible?
      @number % @divisor == 0
    end
    
    def divide_number
      @number = @number / @divisor
    end
    
    def push_prime_to_result
      @primes << @divisor
    end
    
    def increment_divisor
      @divisor += 1
    end
end

prime_factors_spec.rb

require_relative '../src/prime_factors'

RSpec.describe PrimeFactors do
  describe 'PrimeFactors::of()' do
    it 'returns 1, given 1' do
      expect(PrimeFactors::of(1)).to eq([1])
    end
    
    it 'returns [2], given 2' do
      expect(PrimeFactors::of(2)).to eq([2])
    end
    
    it 'returns [3], given 3' do
      expect(PrimeFactors::of(3)).to eq([3])
    end
    
    it 'returns [2, 2], given 4' do
      expect(PrimeFactors::of(4)).to eq([2, 2])
    end
    
    it 'returns [5], given 5' do
      expect(PrimeFactors::of(5)).to eq([5])
    end
    
    it 'retrurn [2, 3], given 6' do
      expect(PrimeFactors::of(6)).to eq([2, 3])
    end
    
    it 'returns [7], given 7' do
      expect(PrimeFactors::of(7)).to eq([7])
    end
    
    it 'returns [2, 2, 2], given 8' do
      expect(PrimeFactors::of(8)).to eq([2, 2, 2])
    end
    
    it 'returns [3, 3], given 9' do
      expect(PrimeFactors::of(9)).to eq([3, 3])
    end
    
    it 'returns [2, 3, 5, 7], given 2 x 3 x 5 x 7' do
      expect(PrimeFactors::of(2*3*5*7)).to eq([2, 3, 5, 7])
    end
  end
end