Our textbook’s implementation of a linked queue makes use of a sentinel
node to avoid the need to treat enqueueing into an empty queue and
dequeing the last element as special cases. This is fine, but it
would also be reasonable, and slightly more memory efficient, to
make do without the sentinel node. For this exercise, you will
develop an alternate implementation of the LQueue class that follows
this design.
Complete the implementation of LQueue.java. Use the provided unit
tests to confirm that the behavior is correct.
There are some questionable design decisions in the way the author’s of our textbook chose to implement their array-based queue:
It probably isn’t a good idea to maintain a separate maxSize
variable to track the capacity of the queue. This information is
already accessible as queueArray.length. Storing the same
piece of information in two different places introduces unnecessary
complexity and opens the door to bugs.
The authors describe two possible approaches for representing the front and rear of the queue:
“One obvious solution is to keep an explicit count of the number of elements in the queue […]. Another solution is to make the array be of size n+1, and only allow n elements to be stored. Which of these solutions to adopt is purely a matter of the implementor’s taste in such affairs. Our choice here is to use an array of size n+1.”
While it’s true that either approach will work, maintaining an explicit count of the number of elements stored leads to a cleaner solution.
Once again, their array-based implementation does not make use of dynamic arrays to enable arbitrarily large queues.
The dequeue and clear methods interfere with garbage collection
by maintaining unused references to elements that are no longer
stored in the Queue.
Download the following Java files:
Complete the implementation of AQueue.java to address all four of
the issues above. You are welcome to refer to the provided OpenDSA
AQueue implementation, but keep in mind that most of your methods
will look very different. For example, your length method should
just return the value of a size variable. Use the provided unit
tests to confirm that the behavior is correct.
We’ve discussed the performance characteristics of queue operations
for both array-based and linked-list-based queues and determined that
all operations are O(1) for both (amortized O(1) in the case of
enqueuing into an array-based queue). This raises the question of
whether one or the other is faster in practice. Once you’ve
completed LQueue.java and AQueue.java, run the following driver to
perform an empirical comparison between the two:
Is one faster than the other? Is that result consistent if you change the number of operations?
Submit LQueue.java and AQueue.java through Canvas.