polynomial_alech.rb

class Fixnum
    # returns '+' for positive numbers, '-' for negative and '' for 0
    def sign
        case self <=> 0
        when 0
            then ''
        when 1
            then '+'
        when -1
            then '-'
        end
    end
end

class Polynomial
    def initialize(coefficients)
        if coefficients.size < 2 then
            raise ArgumentError, "Need at least 2 coefficients."
        end
        @coefficients = coefficients
    end

    # String representation of the object
    def to_s
        result = ''
        @coefficients.reverse.each_with_index do |c, exp|
            # ignore the ones with 0 as coefficient
            next if c == 0
            result = c.sign + formatted_coeff_abs(c) + x_to_n(exp) + result
        end
        # if the result starts with a '+', we should strip it
        result.sub!(/^\+/, '')
        # if the result is empty, it is the constant 0 polynomial
        result == "" ? "0" : result
    end

    private
    # 'x^n' for n > 1, 'x' for n == 1 and '' for n == 0
    def x_to_n(n)
        case n
        when 1
            then "x"
        when 0
            then ""
        else "x^#{n}"
        end
    end

    # The absolute value of the coefficient as a string, the empty
    # string if the coefficient is 1
    def formatted_coeff_abs(coefficient)
        coefficient.abs == 1 ? "" : coefficient.abs.to_s
    end
end