prime_factors_a.rb

def prime_factors(num)
  return [num] if num <= 1
  
  result = []
  until num == 1
    for i in (2..num)
      if num % i == 0
        result << i
        num /= i
        break
      end
    end
  end
    
  return result
end

prime_factors_final.rb

def prime_factors(num)
  return [num] if num <= 1
  
  result = []
  i = 2
  
  until num == 1
    if num % i == 0
      result << i
      num /= i
      i = 2
    else
      i += 1
    end
  end
    
  result
end