marcminneman.rb

class Polynomial < String
   def initialize(coefficient_array)
      raise ArgumentError, "Need at least 2 coefficients." if coefficient_array.length < 2	#minimum term count
      expression = ''; coefficient_array.each_with_index {|c,i| expression += build_term(c,coefficient_array.length-(i+1))}  #build expression one term at a time
      super(expression.sub(/^\+/,'').sub(/^$/,'0'))	# tidy up: (1) remove starting plus sign (2) handle empty expression.
   end
	
   private
	
   def build_term(c,e) # c = coefficient : e = current exponent
      # build the term only if coefficient is no equal to zero
      c != 0 ? "#{build_sign(c)}#{build_coefficient(c)}#{build_variable(e)}#{build_exponent(e)}" : ''
   end
	
   def build_sign(c)
      c > 0 ? '+' : '-'
   end
	
   def build_coefficient(c)
      # coefficient is supressed if 1 or -1
      c.abs!=1 ? c.abs : ''
   end
	
   def build_variable(e)
      # variable is supressed if exponent is 0
      e>0 ? 'x'  :  ''
   end
	
   def build_exponent(e)
      # exponent is supressed if 1 or 0
      e>1 ? "^#{e}" : ''
   end
	
end