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by Bryan Donovan

If you've ever created a web application that deals with scheduling recurring
events, you may have found yourself creating a method to convert a list of days
into a more human-readable string.

For example, suppose a musician plays at a certain venue on Monday, Tuesday,
Wednesday, and Saturday. You could pass a list of associated day numbers to your
object or method, which might return "Mon-Wed, Sat".

The purpose of this quiz is to find the best "Ruby way" to generate this
sentence-like string.

Basically, the rules are:

	* The class's constructor should accept a list of arguments that can be day
	  numbers (see day number hash below), day abbreviations ('Mon', 'Tue', etc.),
	  or the full names of the days ('Monday', 'Tuesday', etc.).
	* If an invalid day id is included in the argument list, the constructor
	  should raise an ArgumentError.
	* The days should be sorted starting with Monday.
	* Three or more consecutive days should be represented by listing the first
	  day followed by a hyphen (-), followed by the last day of the range.
	* Individual days and the above day ranges should be separated by commas.
	* The class should number days (accepting Integers or Strings) as follows:
	    1:  Mon
	    2:  Tue
	    3:  Wed
	    4:  Thu
	    5:  Fri
	    6:  Sat
	    7:  Sun
	* The class needs a method named #to_s that returns the day range string.
	  Here are some example lists of days and their expected returned strings:
	    1,2,3,4,5,6,7:  Mon-Sun
	    1,2,3,6,7:      Mon-Wed, Sat, Sun
	    1,3,4,5,6:      Mon, Wed-Sat
	    2,3,4,6,7:      Tue-Thu, Sat, Sun
	    1,3,4,6,7:      Mon, Wed, Thu, Sat, Sun
	    7:              Sun
	    1,7:            Mon, Sun
	    1,8:            ArgumentError

This is not intended to be a difficult quiz, but I think the solutions would be
useful in many situations, especially in web applications. The solution I have
come up with works and is relatively fast (fast enough for my purposes anyway),
but isn't very elegant. I'm very interested in seeing how others approach the
problem.