tony_chen.rb

# Loops through coefficient array in order
# => If the coefficent is 0, skip to next term
# => Get operator value and absoluete coefficent value
# => Appends the term <operator><coefficient>x^<term> to pretty print string
# => Return pretty print string or 0 if pretty print string is empty
class Polynomial

  def initialize(coefficient_array)
    raise ArgumentError, 'Need at least 2 coefficients' if coefficient_array.size < 2
    @coefficient_array = coefficient_array
  end
  
  def pretty_print
    print_string = ""
    coefficient_array = @coefficient_array
    current_coefficient = @coefficient_array.size
    
    coefficient_array.each_with_index do |coefficient, term|
      current_coefficient -= 1
      next if coefficient == 0
      
      operator = get_operator_by_coefficient_and_term(coefficient, term)
      coefficient = coefficient.abs
      coefficient = "" if coefficient.abs == 1

    case current_coefficient
      when 0
        print_string << "#{operator}#{coefficient}"
      when 1
        print_string << "#{operator}#{coefficient}x"
      else
        print_string << "#{operator}#{coefficient}x^#{current_coefficient}"
      end
    end

    # empty string if the array only passes in 0's  
    print_string == "" ? "0" : print_string
  end
  
  def get_operator_by_coefficient_and_term(coefficient, term)    
    if coefficient > 0
      if first_term?(term)
        ""
      else
        "+"
      end
    elsif coefficient < 0
      "-"
    else
      ""
    end
  end
  
  def first_term?(term)
    term == 0
  end
  
  def to_s
    pretty_print
  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([-5]).to_s