Prime Numbers Kata • Ruby Undergroud

primer.rb

class Primer

  attr_accessor :num

  def initialize(num)
    @num = num
  end

  def run
    arr = []
    return arr if num <= 1
    n = 2

    while true
      if divided_by? n
        arr << n
        arr += Primer.new(num / n).run
        return arr
      else
        n += 1
      end
    end
    arr
  end

  private

  def divided_by?(divider)
    num % divider ==  0
  end

  def leftover(divider)
    num / divider
  end
end

describe Primer do

  it 'returns empty array for 0' do
    expect(Primer.new(0).run).to eq []
  end

  it 'returns empty array for 1' do
    expect(Primer.new(1).run).to eq []
  end

  context 'prime numbers' do
    [2, 3, 5, 7, 11, 13, 17].each do |n|
      it "returns a single element array with itself #{n}" do
        expect(Primer.new(n).run).to eq [n]
      end
    end
  end

  [
    [4, [2, 2]],
    [6, [2, 3]]
  ].each do |input, output|
    it "returns #{output} for #{input}" do
      expect(Primer.new(input).run).to eq output
    end
  end
end