addition_arrays.rb

class Addition
attr_reader :arr1, :arr2


  def initialize(arr1, arr2)
    @arr1 = arr1
    @arr2 = arr2
    @sum = []
  end

  def assign_based_on_size
    if @arr1.size > @arr2.size
      @longer = @arr1
      @shorter = @arr2
    else
      @longer = @arr2
      @shorter = @arr1
    end
  end

  def longer
    @longer ||= assign_based_on_size && @longer
  end

  def shorter
    @shorter ||= assign_based_on_size && @shorter
  end

  def sum
    counter = 0
    longer.reverse.each.with_index do |n, i|
      @sum[i] = n + shorter.reverse[i].to_i + counter
      counter = 0
      while @sum[i] >= 10
        counter += 1
        @sum[i] -= 10
      end
    end
    if counter > 0
      @sum << counter
    end
    p @sum.reverse
  end
end

example = Addition.new([9,2,3,5,2,3,4][1,3,4,5,5])