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COMP 250 Assignment 3

 Assignment 3

COMP 250 Winter 2020
posted: Monday, March 9, 2020
due: Monday, March 23, 2020 at 23:59
Learning Objectives
This assignment aims at building on what we have seen in assignment 2, where we navigated
through list-like objects, to start working with non-linear data structures. In this assignment,
you will implement a derivative of a Binary Search Tree and execute several methods that iterate
through trees. The objective is to familiarize yourself with the implementation of this Abstract
data type, probably the most discussed one in the course. More specifically, you will be applying
concepts seen through the in-class discussion of recursion, trees and how to navigate them, and
binary search trees, as well as some principles we will formalize when we discuss heaps.
General Instructions
• Submission instructions
– Late assignments will be accepted up to 2 days late and will be penalized by 10 points per
day. Note that submitting one minute late is the same as submitting 23 hours late. We
will deduct 10 points for any student who has to resubmit after the due date (i.e. late)
irrespective of the reason, be it wrong file submitted, wrong file format was submitted
or any other reason. This policy will hold regardless of whether or not the student can
provide proof that the assignment was indeed “done” on time.
– Don’t worry if you realize that you made a mistake after you submitted: you can submit
multiple times but only the latest submission will be evaluated. We encourage you
to submit a first version a few days before the deadline (computer crashes do happen
and myCourses may be overloaded during rush hours).
– Please store all your files in a folder called “Assignment3”, zip the folder and submit it
to MyCourses. Inside your zipped .senior, there must be the following file.
∗ CatTree.java
Do not submit any other files, especially .class files. Any deviation from these
requirements may lead to lost marks
• It does not matter whether or not you create a package to store all these classes. It is up to
you to decide whether you’d like to have a package or not.
• You are given class templates to complete. You can only change the code of these classes
within the methods containing the comments ”YOUR CODE GOES HERE”. You cannot
change any method headers unless a comment specifies you can, and even then, the only
changes you can make are to add exception handling. If you change a method header, we
might not be able to grade you and you may receive a grade of zero. Read the comments in
the templates carefully.
• Requests to evaluate the assignment manually shall not be entertained, so please make sure
that you follow the instruction closely or your code may fail to pass the automatic tests. Note
that for this assignment, you are NOT allowed to import any other class than what is already
imported in the template. Any failure to comply with these rules will give you an
automatic 0.
• We have included with these instruction a tester class. If your code fails the tests performed
by the tester, it means that there is a mistake somewhere. Even if your code passes those
tests, it may still contain some errors. We will test your code on a much more challenging set
of examples. We therefore highly encourage you to modify the tester class and expand it.
• You will automatically get 0 if your code does not compile.
• Failure to comply with any of these rules will be penalized. If anything is unclear, it is up to
you to clarify it by asking either directly a TA during office hours, or on the discussion board
on Piazza.
• If you submit just the java file (not in a zip), you will receive a grade of zero.
A Crowded Cat Cafe Chain
You have just been named CEO of a chain of Cat Cafes. A cat cafe is a coffee shop in which cats
are roaming and interact with customers. At the time of your promotion, you are informed that the
chain does not have any repository of the cats, and maintains no information about their seniority.
You are extremely upset upon hearing this as you understand those cats are your most important
staff members and, like any other employees, deserve salary and working conditions that improve
with seniority.
You immediately call your best friend, who recently told you they were a computer science expert.
You expect them to build you a state-of-the-art database for all your cats. Upon hearing your
request, they seem to hesitate a bit and, after a moment of wavering, confess that they are only
taking their second computer science course and cannot yet build a professional database. However,
they recently learned about binary search trees and how they can be leveraged to efficiently access
data. They explain they have not yet learned about heaps and as such their idea does not utilize
trees to their full potential, but it should still provide a solution to your problem. They email you
a quick draft and you start getting excited about it (after all, cats do love trees), until they specify
they cannot help you because they are currently busy with their new job, which they then begin
describing. It sounds pretty cool until they try to convince you to invest in their ”company” by
buying a bunch of knives to re-sell. You try to tell them it sounds like a pyramid scheme but they
start yelling something about those only ever occurring in Ancient Egypt, and they hang up on
you. You try to call them back but it appears they blocked your number.
It looks like you are going to have to build your tree on your own. You have a second look at their
email to see what you have to work with, and what is left to do.
The database of all cats is represented by a ternary tree CatTree. This tree has a single field
root which contains a reference to the root node. The nodes are defined by a private nested class
CatNode. Each CatNode is associated with data stored in a CatInfo object (code provided).
This CatInfo class stores data into the following fields:
• String name: the name of the cat.
• int monthHired: the time at which the cat was hired. You manage your business month
to month, so for simplicity, since the company began operating on January 1st, 2000, you
are identifying each month of operation with a simple integer associated with the number of
months elapsed since then. Thus, January 12, 2000 was in month 0. November 25, 2015 was
in month 191, and March 2020 is month 243.
• int furThickness: the average thickness of the cat’s fur in millimeters (measured profes￾sionally), stored as an integer.
• int nextGroomingAppointment: the month in which we expect the next grooming appoint￾ment, once again stored as an integer.
• int expectedGroomingCost: the expected cost of the next grooming appointment, in dollars.
The CatTree class contains a CatNode inner class, and a field root, which contains the root node
of the tree. It also implements Iterable and includes a CatTreeIterator inner class. CatTree
contains several already implemented public methods, as well as a constructor. Those methods,
called on the tree, call the CatNode functions you will implement.
The CatNode inner class contains the information about the tree structure.
• CatInfo data: the CatInfo object with the data for this cat.
• CatNode senior: this cat and all the children of its node have more seniority than the current
node’s cat.
• CatNode junior: this cat and all the children of its node have less seniority than the current
node’s cat.
• CatNode same: this cat and all the children of its node have exactly the same seniority than
the current node’s cat.
In addition, in the structure of the tree, CatNodes with equal seniority should be sorted in decreasing
order of fur thickness.
Build your database. Note: you will be tested on time efficiency, so make sure to
implements methods based on what was seen in class!
[12 points] First, consider CatTree.addCat(). This method takes as input a CatInfo object,
converts it to a CatNode and calls CatNode.addCat() with the CatNode as input. You are
asked to implement CatNode.addCat().
Given a CatNode c and a CatNode catToAdd, c.addCat(catToAdd) adds the CatNode catToAdd
in the tree with root c accordingly to the rules explained before : if the cat to be added is more
senior than the cat at the root, then it has to be added to the subtree with root c.senior. In
the case where the CatNode to be added has the same seniority as the root, the organization
depends on fur thickness. If the cat to be added has thicker fur than the cat at the root, it
should be stored in the root node, and the cat previously in the root node should be stored
in the subtree with root c.same. The method should return the root of the tree it was called
To clarify, let us give some examples. Let us define a CatNode cA, associated with cA.data.name
Alice, cA.data.monthHired equal to 87, and cA.data.furThickness equal to 50. For sim￾plicity, from here on, we will refer to this as declaring a CatNode cA −→ (Alice, 87, 50).
Let’s build a tree with cA at its root, which also includes cB −→ (Bob, 88, 60), cD −→
(Doughnut, 85, 50), cE −→ (Eleanor, 85, 45), cF −→ (F elix, 85, 60), and cH −→ (Hilda, 95, 55)
When the fields senior, same or junior are not null, we represent them with an arrow to
the corresponding CatNode. Note that we name the nodes base on the CatInfo they initially
contain, but their contents can get swapped with other nodes, so CatNode cA.data might not
[9 points] Implement fluffiest. When called on a CatNode c, the integer c.fluffiest() should
be the fur thickness of the CatNode with greatest fur thickness in the tree with root c. Do
not modify the tree structure.
On the example given to you in the previous question, cA.fluffiest() should return 60 and
cD.fluffiest() should return 50.
[8 points] Implement hiredFromMonths. When called on a CatNode c, the integer
c.hiredrFromMonths(monthMin, monthMax) should be the number of cats hired from month
monthMin to monthMax (including those two months), that is in the tree with root c. If
monthMin > monthMax, this should return 0. Do not modify the tree structure.
On the example from the question asking you to code mostSenior, cA.hiredFromMonths(86, 88)
should return 4 (corresponding to CatNode cG, cC, cA and cB).
[8 points] Implement fluffiestFromMonth. When called on a CatNode c,
c.fluffiestFromMonth(month) should return the CatInfo linked to the cat with thickest
fur, hired in the month month, in the tree with root c. If no such cat is found, null should
be returned. Do not modify the tree structure.
On the example from the question asking you to build mostSenior, cA.fluffiestFromMonth(85)
should return cF.data, and so should cF.fluffiestFromMonth(85), but cD.fluffiestFromMonth(85)
should return cD.data.
[15 points] Implement costPlanning. When called on a CatNode c, the array c.costPlanning(n),
which should have length n, should have in its i-th cell, how much you should spend on month
(243 + i) for all the scheduled grooming appointments over this time period, in the tree with
root c. Here, month 243 is March 2020, so at i=0, you are planning the cost for this month,
and at index 1, you are planning the costs for month 244, which is next month (April). The
argument n will always be a positive integer. Do not modify the tree structure.
Let us modify the example given in the question asking you to implement mostSenior to
display the month planned for the next grooming appointment and the associated cost.
(Coco, 249, 23)
On this example, cA.costPlanning(7) should return the array {0, 46, 0, 42, 5, 50, 60} :
in month 243, there is no cost to plan for grooming, but in month 249, Cats Coco, Felix and
Gaia will need to be groomed, for a cost of 23 + 26 + 11 = 60. Similarly, cB.costPlanning(7)
should return the array {0, 46, 0, 0, 0, 50, 0}. Note: Bob and Hilda have higher groom￾ing cost because they bite. Doughnut gets a discount because he no longer has teeth.
You can use the iterator described in the next task to solve this problem
[18 points] Implement the inner class CatTreeIterator. The method CatTree.iterator() re￾turns a CatTreeIterator object which can be used to iterate through all the cats in the tree.
The iterator should access the cats from most senior to most junior. In the case in which cats
have been hired within the same month, the iterator should access cats based on fur thickness:
cats with thicker fur should be access later.
We will test your iterator by examining the order in which the cats are accessed. It is ok
if your iterator uses an ArrayList to store references to all the cats in the tree. We have
imported the class in the template. There are more space efficient ways to implement an
iterator for trees, but you will not be tests on space efficiency.
Good luck!
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