rohitsasikumar.rb

require 'test/unit'

# Class for printing the polynomial in string form given the coefficients in an array. 
# Assumptions: Coefficents are whole numbers only.
class Polynomial
  def initialize (arg)
    raise ArgumentError, "Need at least 2 coefficients" if arg.size < 2
    @coefficients = arg
  end
  
  # Function for printing the polynomial
  def to_s    
    # create an array of the variable and degrees. For eg, if the number of coefficients is 3, then the array of is ["x^3", "x^2", "x", ""]
    variable_degree = Array.new(@coefficients.size) {|i| i}
    variable_degree.reverse!.collect! do|i|
      if i == 1
        "x"
      elsif i >= 1
        "x^#{i}"
      end
    end
    
    variable_degree.compact!
    variable_degree << ""
    
    # make a sum of the terms of the polynomial using the coefficients and the variable_degree array
    expr = @coefficients.inject('') do |sum,obj|
      if obj == 0
        variable_degree.shift
        next sum
      elsif obj == 1
        asd = '+'
      elsif obj == -1
        asd = '-'
      elsif obj > 1
        asd = '+' + obj.to_s
      else
        asd = obj.to_s
      end
      
      sum + asd + variable_degree.shift
    end
    
    expr = "0" if expr.eql? "" # If result is "" string then make it "0"
    expr.sub!(/^\+/,'') # remove the leading '+' sign
    expr
  end
end

# unit tests for testing the Polynomial class
class Polynomial_Test < Test::Unit::TestCase
  def setup
    @p1 = Polynomial.new([-3,-4,1,0,6])
    @p2 = Polynomial.new([1,0,2])
    @p3 = Polynomial.new([-1,-2,3,0])
    @p4 = Polynomial.new([0,0,0])
  end
 
  def test_first_negative
    assert_equal("-3x^4-4x^3+x^2+6", @p1.to_s)
  end
 
  def test_simple
    assert_equal("x^2+2", @p2.to_s)
  end
 
  def test_first_minus_one
    assert_equal("-x^3-2x^2+3x", @p3.to_s)
  end
 
  def test_all_zero
    assert_equal("0", @p4.to_s)
  end
 
  def test_error
    e = assert_raise(ArgumentError) { Polynomial.new([1]) }
    assert_match(/Need at least 2 coefficients/, e.message)
  end
  
  def test_misc
    assert_equal("-x^3+2x^2-3x-4", Polynomial.new([-1,2,-3,-4]).to_s)
    assert_equal("x^4+3x^2+5", Polynomial.new([0,1,0,3,0,5]).to_s)
    assert_equal("9x^5", Polynomial.new([9,0,0,0,0,0]).to_s)
  end
end