polynomial.rb

class Coefficient
  def initialize(coefficient, power)
    @coefficient = coefficient
    @power = power
  end

  def format_coefficient
    case @coefficient.abs
    when 1
      ""
    else
      "#{@coefficient.abs}"
    end
  end

  def format_power
    case @power
    when 0
      ""
    when 1
      "x"
    else
      "x^#{@power}"
    end
  end

  def sign
    if @coefficient < 0
      "-"
    elsif @coefficient > 0
      "+"
    end
  end

  def to_s
    if @coefficient == 0
      ""
    else
      "#{sign}#{format_coefficient}#{format_power}"
    end
  end
end

class Polynomial
  def initialize(coefficients)
    @coefficients = coefficients.map.with_index {|coefficient, idx| Coefficient.new(coefficient, idx)}
  end

  def to_s
    @coefficients.join("").gsub(/^\+/, '')
  end
end

puts Polynomial.new([3, 4, -2, 1, 0, 1, 2])