benoitdaloze.rb

# Benoit Daloze
# Ruby Programming Challenge For Newbies #4
# pretty-print polynomials
#
# My solution use Enumerable#inject to build the String,
#   with every "monomial" splitted in 3 parts : sign, coefficient and variable
class Polynomial
	def initialize(coef)
		raise ArgumentError, "Need at least 2 coefficients" if coef.size < 2
		@coef = coef
	end
	
	def to_s
		return '0' if @coef.all? { |c| c == 0 }
		(0...@coef.length).inject("") { |s, i|
			coef, pow = @coef[i], @coef.length-1-i
			if coef == 0
				s
			else
				s +
				(coef > 0 ? '+' : '-') + # sign
				(coef.abs == 1 && pow != 0 ? '' : coef.abs.to_s) + # coef
				(pow < 2 ? 'x'*pow : "x^#{pow}") # var
			end
		}.sub(/^\+/, "")
	end
end