https://gist.github.com/280aa4797a580fb8ae75

polynomial.rb

# My solution to: https://gist.github.com/280aa4797a580fb8ae75

class Polynomial
  class Term
    attr_reader :power, :coefficient

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

    def to_s
      return "" if coefficient.zero?
      sign = (coefficient > 0) ? "+" : "-" 
      return "#{sign}#{coefficient.abs}x^#{power}"
    end 
  end 

  def initialize(coefficients)
    raise ArgumentError, "Need at least 2 coefficients." if coefficients.size < 2 
    @terms = []
    coefficients.each_with_index { |coef, index| @terms << Term.new(coefficients.size - index - 1, coef) }
  end 

  def to_s
    s = String.new
    @terms.each { |t| s << t.to_s }
    s = s.gsub(/\+1/, '+').gsub(/\-1/, '-').gsub(/\^1/, '').gsub(/x\^0/, '') 
    s = s[1..-1] if s.start_with? "+" 
    return s.size == 0 ? "0" : s 
  end 
end