remycoutable.rb

# Ruby Programming Challenge For Newbies
# Solution for RPCFN: Ruby**Fun (#4)
# 
# Creator : Rémy COUTABLE 2009 (http://remycoutable.fr)

class Polynomial
  attr_reader :coeffs
  
  # coeffs should be an Array of relative integer
  def initialize(coeffs)
    raise ArgumentError, "Need at least 2 coefficients." if coeffs.size < 2
    @coeffs = coeffs.reverse
  end
  
  def to_s
    @result = ""
    (@coeffs.size - 1).downto(0) do |power|
      @result += print_coeff_and_power(@coeffs[power], power)
    end
    @result.empty? ? "0" : @result
  end
  
  private
  def print_coeff_and_power(coeff, power)
    "#{print_sign(coeff)}#{print_coeff(coeff, power)}#{print_power(power, coeff)}"
  end
  
  # only display "+" for a positive integer, and not for the first coeff
  def print_sign(coeff)
    "+" if coeff > 0 && !@result.empty?
  end
  
  # coeff is a relative integer
  def print_coeff(coeff, power)
    (coeff == -1 && power > 0) ? "-" : coeff if display_coeff?(coeff, power)
  end
  
  def display_coeff?(coeff, power)
    return case coeff
    when 0
      false
    when 1
      power == 0
    else
      true
    end
  end
  
  # power is an integer
  def print_power(power, coeff)
    "x#{"^#{power}" if power > 1}" if power > 0 && coeff != 0
  end
  
end

puts Polynomial.new([-3,-4,1,0,6]).to_s
puts Polynomial.new([1,0,2]).to_s
puts Polynomial.new([-1,-2,3,0]).to_s
puts Polynomial.new([0,0,0]).to_s
puts Polynomial.new([0,1,2,3,4]).to_s
puts Polynomial.new([-5,-4,-3,-2,-1]).to_s
puts Polynomial.new([3,2,1]).to_s