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# Fundamentals of Data Structures Assignment 2

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Further Instructions:
• This assignment consists of 3 problems and is designed to let you practice on recursion versus
iteration, linear structures such as lists, stacks, queues, and some Java programming concepts.
• You are expected to apply appropriate OOP principles in the design of your programs.
• Feel free to design additional classes or members as you deem necessary.
• Include your additional explanations, analysis, and I/O test results in a file named a2sol.pdf.
1
Problem 1 (30 points): Enumeration of Coin Change Making:
Develop a program in a class named Coins that includes a method with the signature
ways( int money) that uses recursion (possibly through recursive helper methods) to enumerate
the distinct ways in which the given amount of money in cents can be changed into quarters,
dimes, nickels, and pennies. Test your program from the main() method for various amounts of
change by prompting the user to enter an amount in cents. For example, suppose the entered
amount is 17. Then there are 6 ways to make change for this amount. Here is what exactly the
I/O printout should look like:
Enter an amount in cents:
17
This amount can be changed in the following ways:
1) 1 dime, 1 nickel, 2 pennies
2) 1 dime, 7 pennies
3) 3 nickels, 2 pennies
4) 2 nickels, 7 pennies
5) 1 nickel, 12 pennies
6) 17 pennies
In your program you may use additional private helper methods, constructors, etc., as you deem
necessary.
Restriction: Other than the I/O types, you may use only a constant amount of additional memory
cells for your local variables and method parameters. So, you are not allowed to use elaborate
structures such as arrays, lists, stacks or queues that may hold more than a constant number of
elements.
EECS2011ON: Fundamentals of Data Structures
Assignment 2
Due: 9 pm, Friday, February 14, 2020
• This is an individual assignment; you may not share code with other students.
• Read the course FAQ on how to submit assignments and the marking scheme.
• Print your name, EECS account and student ID number on top of EVERY file you
submit.
Department of EECS
York University
Term: Winter 2020
Instructor: Andy Mirzaian
2
Problem 2 (40 points): A Walk on the Hypercube:
The unit hypercube in the 𝑛-dimensional space is the set of all points (𝑥1, 𝑥2, … , 𝑥𝑛) in that space
such that its coordinates are restricted to be 0 ≤ 𝑥𝑖 ≤ 1 for 𝑖 = 1. . 𝑛. This hypercube has
2
𝑛
corners. Each coordinate of a corner is either 0 or 1. Each edge of the hypercube connects a pair
of corners that differ in exactly one of their coordinates. A walk on the hypercube starts at some
corner and walks along a sequence of edges of the hypercube so that it visits each corner exactly
once. There are many such walks possible. The following figure shows an example for 𝑛 = 3. The
edges of the (hyper)cube along the walk are thickened.
𝒙𝟏
𝒙𝟑
𝒙𝟐
000 100
110
011 111
001 101
010
A Walk:
000
100
110
010
011
111
101
001
The problem: for any given 𝑛, output the sequence of corners visited along a walk of the 𝑛-
dimensional hypercube.
We want to study recursive and iterative solutions to this problem. In order to do that, design a
Hypercube class that (among possibly other members) includes the following:
a) A nested class named Corner. An instance of this type represents a corner of the hypercube
and occupies O(n) memory cells.
b) A recursive method named recursiveWalk() to solve the above problem.
The parameters and local variables of this method can only be primitives or Corner types.
c) An iterative method named iterativeWalk() to solve the above problem using a single queue.
The elements of this queue, as well as the other local variables and method parameters, can
only be primitives or Corner types.
(Note: We know that any recursive algorithm can be converted to an equivalent iterative one
by simulating a recursion stack. However, here you are forbidden to use a stack or any structure
that may act as one such as an array or a list. Java has a Queue interface, not a class. But it has
an ArrayDeque class that can do the job of a queue as well as other lists. You may either design
your own Queue class or use the queue methods in ArrayDeque. You are not allowed to use
the stack or other methods in ArrayDeque. In other words, use ArrayDeque only as a queue,
i.e., a First-In-First-Out list.)
d) Explain the running times of your solutions in parts (b) and (c) in a2sol.pdf.
e) The main() method of Hypercube class should test recursiveWalk and iterativeWalk for at
least the dimensions 𝑛 = 3, 4, 5. Report the I/O results in a2sol.pdf.
3
Problem 3 (30 points): Augmented Stack with getMin:
An AugmentedStack s is an ADT that maintains any generic stack with comparable element type
under the following operations, each requiring O(1) worst-case time:
s.push(x): Insert element x on top of s.
s.pop(): Remove and return the top element of s (if not empty).
Return null if s is empty.
s.getMin(): Return the minimum element on s (if not empty).
Return null if s is empty.
(Upon return from this method, s should be in the same
state as it was before this method was called. In particular,
the minimum element is not removed from s.)
Also include the usual operations s.isEmpty() and s.top() with the same meaning as for
conventional stacks that run in O(1) worst-case time.
Design and analyze a data structure that implements this ADT with the specified running times.