johnmcdonald.rb

#
# pretty polynomial print
#
# - passed all unit tests
#
class Polynomial
  attr_reader :coefficients
  
  def initialize(coefficients)
    raise ArgumentError, 'Need at least 2 coefficients' if coefficients.size < 2
    coefficients.each do |c|
      raise ArgumentError, 'Invalid coefficient ' + c.to_s if c.class != Fixnum
    end
    @coefficients = coefficients
  end

  def to_s
    str ||= String.new
    @coefficients.each_index do |i|
      #
      # Checking the conditions:
      #  - if 1st coefficient pos or neg
      #  - if subsequent coefficients pos or neg
      #  - if a coefficient is zero
      #  - if a coefficient is a '1' (pos or neg)
      #  - if coefficient of zero term (x^0) is '1'
      #  - check the degree of the term (add '^')
      case
      when @coefficients[i] == 0 # if all zeroes
        str << '0' if str == ''
      when i == @coefficients.size-1 # if the last cofficient
        str << '+' unless @coefficients[i] < 0 # is positive and is the last coefficient (constant), add '+'
        str << @coefficients[i].to_s # add the last coefficient
      else
        str << '+' unless i == 0 or @coefficients[i] < 0 # is positive and not first coefficient, add '+      
        str << '-' if @coefficients[i] < 0 and @coefficients[i].abs == 1 # is negative, is '1' coefficient, add '-'
        str << @coefficients[i].to_s unless @coefficients[i].abs == 1 # don't add a '1' coefficient
        str << 'x'
        str <<  '^' + (@coefficients.size-(i+1)).to_s if i < @coefficients.size-2 # check the degree
      end # end case
    end # end do
    str # return the string
  end

end

p = Polynomial.new([-3,-4,1,0,6])
puts p.to_s
p = Polynomial.new([0,0,-0])
puts p.to_s
p = Polynomial.new([-20,0,18,-12,7,-4,0,-3,-4,1,-1,-6])
puts p.to_s
p = Polynomial.new([-20,0])
puts p.to_s