solution to Ruby quiz

gistfile1.rb

class ArgumentError < StandardError
end

class Polynomial
  def initialize(coeffs)
    raise ArgumentError, "Need at least 2 coefficients" unless coeffs.length > 1
    @coeffs = coeffs
  end
  def to_s
    # `pairs' is an array that encodes non-zero terms occuring in the polynomial.
    pairs = @coeffs.reverse.each_with_index.reject { |c, i| c == 0 }.reverse
    if pairs.empty?
      # If there are no non-zero terms, then we are dealing with the zero polynomial.
      "0"
    else
      # Otherwise format each term, join all the terms interspersing them
      # with the "+" sign and replace all occurences of "+-" with "-".
      pairs.map { |c, i| term c, i }.join("+").gsub(/\+-/, "-")
    end
  end
  private
  # Format the term cx^i approriately for pretty-printing.
  # Omit the coeffiecient c if it is -1 or 1, but leave it
  # in the constant term.
  def term(c, i)
    d = case c
        when -1 then "-"
        when  1 then ""
        else "#{c}"
        end
    case i
    when 0 then "#{c}"
    when 1 then "#{d}x"
    else "#{d}x^#{i}"
    end
  end
end