gistfile2.rb

require 'test/unit'
require 'test/unit/ui/console/testrunner'
require 'stevewilhelm'
 
class Polynomial_Test < Test::Unit::TestCase
  def setup
    @p1 = Studio831::Polynomial.new([-3,-4,1,0,6])
    @p2 = Studio831::Polynomial.new([1,0,2])
    @p3 = Studio831::Polynomial.new([-1,-2,3,0])
    @p4 = Studio831::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) { Studio831::Polynomial.new([1]) }
    assert_match(/Need at least 2 coefficients/, e.message)
  end
end
 
Test::Unit::UI::Console::TestRunner.run(Polynomial_Test)

stevewilhelm.rb

# From: http://rubylearning.com/blog/2009/11/26/rpcfn-rubyfun-4/
# You just started working for CoolNewCompany which is developing 
# mathematics related software. Since you are new to the team, 
# your boss gives you an easy task to test your abilities. 
# 
# Write a class that pretty-prints polynomials, following some simple rules:
#  - if a coefficient is 1, it doesn’t get printed
#  - if a coefficient is negative, you have to display something like “- 2x^3″, not “+ -2x^3″
#  - if a coefficient is 0, nothing gets added to the output
#  - for x^1 the ^1 part gets omitted
#  - x^0 == 1, so we don’t need to display it


module Studio831
  class Polynomial 
    
    def initialize x
      raise ArgumentError, "Expecting Array", caller if ! x.instance_of?(Array) 
      raise ArgumentError, "Need at least 2 coefficients", caller if x.size <= 1 
      x.each { |v| 
        raise ArgumentError, "Array contains non numeric elements", caller if !v.is_a? Numeric
      }
      @p = x
    end
    
    # Notes: 
    # reverse the array to make the rule tests below easier to test
    # Idea for using inject inspired by Gennady Bystritsky's solution to Roman Numerals 
    # post http://www.ruby-forum.com/topic/198968
    
    def to_s
      str = @p.reverse.each_with_index.inject("") do |s,(c,i)|
        if (c == 0) then                  # rule #3: if a coefficient is 0, nothing gets added to the output     
          e = "" 
        else
          e = "%+d" % c                   # rule #2: if a coefficient is negative, you have to display something like “-2x^3″          
          e.delete! "1" if (c.abs == 1)   # rule #1: if a coefficient is 1, it doesn’t get printed
          e << "x" if (i != 0)            # rule #5: x^0 == 1, so we don’t need to display it
          e << "^%d" % i if (i > 1)       # rule #4: for x^1 the ^1 part gets omitted           
        end
        e + s
      end
      # clean up the special cases of 0 and leading +
      str = "0" if str.empty?
      str.slice!(0) if str[0].chr == "+"
      str
    end
  end
end