Exercise 4.18

> I am having a hard time to understand the question 4.18.  I really don't
> understand the question mean about "boundaries" or what I am looking
> at the problem.  Could you please give me further explaination?

The "boundaries" are the indexes of the first and last element of the
region in question.  The indexes you may use in your formulas are
first, vacant, unknown, and last.  So, for example, at line 3 of the
code, the boundaries of the region of small keys are first and
vacant-1.  The pictures in Fig. 4.30 should be helpful.  (For some of
the lines of the code, the boundaries don't change, so your answers for
each line may be similar.)