josesazo.rb

# polynomial.rb
#
# This is the solution to RPCFN: Ruby**Fun (#4)
# (http://rubylearning.com/blog/2009/11/26/rpcfn-rubyfun-4/).
#
# Here we have two classes: Polynomial and Term.
#
# - Polynomial is pretty simple. On contruction, it accepts an array
#   containing the polynomial's coefficients
# - Polynomial#to_s calls Polynomial#generate just the first time it is
#   called
# - Polynomial#generate populates @terms and injects exponents into
#   place
# - Each Term instance on @terms always holds the coefficient and exponent
#   numbers in spite of having special cases for zeros or ones and thus no
#   need to print them
# - Term#to_s covers the special cases. It filters the output mostly
#   with regular expresions: no arithmetics needed
#
# José Sazo -- jose.sazo@gmail.com

class Polynomial
  attr_reader :coefficients, :terms, :degree

  def initialize(array)
    @coefficients = array
    @degree = @coefficients.length
    @terms = []
    raise ArgumentError, 'Need at least 2 coefficients' unless @degree > 1
  end

  def generate
    @coefficients.each do |c|
      @terms << Term.new(c)
    end
    @terms.inject(@degree - 1) do |n, term|
      term.exponent = n
      n - 1
    end
  end

  def to_s
    generate if @terms.empty?
    output = @terms.join.sub(/^\+/, '')
    return "0" if output.empty?
    output
  end
end

class Term
  attr_accessor :coefficient, :exponent
  
  def initialize(coefficient)
    @coefficient = coefficient
  end

  def to_s
    s = @coefficient.to_s + 'x^' + @exponent.to_s
    s = '+' + s unless @coefficient < 0
    s.slice!("1") if @coefficient.abs == 1 and not @exponent.zero?
    s.sub!(/x\^1$/, 'x')
    s.sub!(/x\^0$/, '')
    return '' if @coefficient.zero?
    return s
  end
end
### Solution code ends here ###

### Testing code begins here ###
# 
# Added my own test cases and adapted the code for MiniTest (Ruby
# 1.9.1's Test::Unit replacement) from
# https://gist.github.com/280aa4797a580fb8ae75

require 'minitest/unit'

MiniTest::Unit.autorun
 
class Polynomial_Test < MiniTest::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])
    @p5 = Polynomial.new([3,-2,+1])
    @p6 = Polynomial.new([-43,0,5,0,-1])
    @p7 = Polynomial.new([2,11])
  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

  # Added by me
  def test_last_plus_one
    assert_equal("3x^2-2x+1", @p5.to_s)
  end

  # Added by me
  def test_last_minus_one
    assert_equal("-43x^4+5x^2-1", @p6.to_s)
  end

  # Added by me
  def test_last_eleven
    assert_equal("2x+11", @p7.to_s)
  end

  def test_error
    e = assert_raises(ArgumentError) { Polynomial.new([1]) }
    assert_match(/Need at least 2 coefficients/, e.message)
  end
end