rpcfn4.rb

class Polynomial
  def initialize args=[]
    raise ArgumentError, "Need at least 2 coefficients." if args.size < 2
    @max_exp = args.size - 1
    @poly = ""

    args.each_with_index do |coef, index|
      # Code reading 101 : 'coef' stands for 'coefficient'.
      next if coef.zero?
      @coef = coef
      @index = index
      add_sign
      add_coef 
      add_exp
    end

    @poly = "0" if @poly.empty?
  end

  def to_s
    @poly
  end

  private
  def add_sign
    if @index > 0 # If this isn't the first argument
      if @coef > 0
        @poly += "+"
      else
        @poly += "-"
      end
    else # If it's the first argument, we don't care about '+'
      if @coef < 0
        @poly += "-"
      end
    end

  end

  def add_coef
    coef = @coef.abs # We only care about the absolute value, here.
    return if coef == 1
    @poly += coef.to_s
  end

  def add_exp
    exponent = @max_exp - @index # Size of the array minus where we are in the array
    return if exponent.zero?
    if exponent > 1
      @poly += "x^#{exponent}"
    else
      @poly += "x"
    end
  end

end