sriramvarahan.rb

=begin
Title:               Ruby Challenge #4
Program Description: Constructing a polynomial given the coefficients
Submitted By:        Sriram Varahan  
=end

class Polynomial
  ##
  # Initialize the coefficients instance variable.
  # raise "ArgumentError" Exception in case the number of coefficients are less than two/
  #
  def initialize(args)
    raise ArgumentError, "Need at least two coefficients!", caller[1..-1] if args.length < 2
    @coefficients = args
  end

  ##
  # This is the method where the polynomial is constructed.
  # The way the method works is as follows:
  # The output variable is an array which holds each term for e.g. "3x^5"
  # The coefficients array is reversed so that the index value would give the number to be raised to.
  # For example: consider input as [2,5,6,7]
  # Reversing this would give us : [7,6,5,2]
  # Now we just need to raise x to the index corresponding to the numbers.
  # 7x^0(illustration), 6x^1 and so on...
  # Now for each value we calculate the sign and the variable part keeping in mind values of 1 and 0.
  # We don't assign a "+" sign in case the number is negative.
  # Now the output holds the terms in the reverse order.
  # We return the output after reversing it, removing the "+" from the first term and converting it to string.
  #
  def construct_polynomial
    output = []
    @coefficients.reverse!

    @coefficients.each_with_index do |coefficient,index|
      # In case of a negative number the sign is already present. 
      sign = (coefficient.to_i < 0)  ? "" : "+"
      unless coefficient.to_i == 0
        variable_part =   index != 0 ? (index == 1 ? "x" : "x^#{index}") : ""
        case
          when coefficient.to_i == -1 then coefficient = "-"
          # Remove 1 form places where there is no variable part.
          # Example : 3x^2 + (remove 1)x + 1(keep 1)
          when (coefficient.to_i == 1 && index != 0) then coefficient = ""
        end
        output << "#{sign}#{coefficient}#{variable_part}"
      end
    end

    output    = output.reverse
    output    << "0"  if output.empty?
    # Remove "+" from the first term
    output[0] = output[0].gsub("+","")
    output    = output.join("")
    output
  end
end

# Usage
puts Polynomial.new([-3,-4,1,0,6]).construct_polynomial
puts Polynomial.new([1,0,2]).construct_polynomial
puts Polynomial.new([0,0,0]).construct_polynomial
puts Polynomial.new([-1,-2,3,0]).construct_polynomial