# Computer Science 343 Data Structures Fall 2012

Dr. Stephen Bloch
office 203 Post Hall
phone 877-4483
office hours TTh 3:00-4:00, W 10:00-1:00, W 2:30-4:00, or by appointment

August 25, 2012

# Course Description

Expand on topics learned in CSC 172. Examine, implement, and analyze common data structures such as stacks, queues, lists, trees, heaps, and graphs. Understand how to choose an appropriate data structure for a real-world problem and use it in solving such problems.

# Subject Matter

This is a course for anybody who’s ever complained about a computer being slow. When faced with a computer program that takes unacceptably long to solve the problem at hand, one option is to buy faster, more expensive computer hardware. But this option has its limits: perhaps your money will run out, or perhaps you’ll upgrade to the fastest computer on the market and still be unsatisfied. Often a better option is to find a more efficient approach to the problem — to re-think the algorithm so that it makes better use of the hardware. A \$1,000 personal computer running a good algorithm can often outperform a \$1,000,000 supercomputer running a bad (though correct) algorithm.

In 1976, Niklaus Wirth (inventor of the Pascal language) wrote a classic computer science textbook entitled Algorithms + Data Structures = Programs. The statement was somewhat oversimplified, but almost forty years later it still carries a lot of truth: a great deal of the work of writing a correct and efficient program consists of choosing algorithms and data structures. Indeed, although Adelphi offers two separate courses CSC 343 (“Data Structures”) and CSC 344 (“Algorithms and Complexity”), the subjects really can’t be separated so easily: many important algorithms only work well with a particular data structure, and many important data structures are motivated by particular algorithms. Accordingly, I plan to teach the two courses as a seamless whole, addressing both algorithms and data structures as they naturally come up.

In this course we’ll learn how to measure the efficiency of an algorithm, independent of language, operating system, or hardware. We’ll survey a variety of techniques for designing efficient algorithms and data structures. Many of these techniques will help you program correctly even when you’re not worried about efficiency.

In the second semester, we’ll learn some additional important algorithms and data structures. We’ll learn how to prove that a given algorithm is “as good as it can get,” in the sense that no algorithm, no matter how clever, will ever be better than this one. Finally, we’ll study problems believed to have no efficient solution by computer program, and even some problems which have no computational solution at all, and how we deal with such problems in reality.

# Course Learning Goals

By the end of this semester, you should be able to

• write and critique proofs by mathematical induction

• read and write algorithms in pseudocode

• offer constructive critiques of other students’ algorithms, data structures, and proofs

• respond constructively to such critiques of your work

• make good asymptotic estimates (in big-O notation) of the running time and memory consumption of a given program

• capture and analyze empirical data to compare the running time of different programs

• implement and use linked lists, array-based lists, stacks, queues, binary and n-ary trees, self-balancing trees, heaps, and hash tables, including the provision of access and traversal methods for these data structures

• implement and compare a variety of algorithms for a single problem, e.g. insertion sort, bubble sort, selection sort, Shell sort, merge sort, Quicksort, tree sort, heap sort, bin sort, bucket sort

# Textbooks

I’ve chosen two textbooks to use throughout the two-semester sequence: they cover a lot of the same topics, but sometimes I like one author’s treatment better than the other’s.

One is the “bible” of algorithms and data structures, Introduction to Algorithms by Cormen, Leiserson, Rivest and Stein (MIT Press 2009, ISBN 0262033844). (The “Rivest” author is the R in the RSA cryptosystem, by the way.) It’s a big, thick book, but relatively inexpensive, because there’s not much second-hand market for it: once you’ve bought it, you’ll probably refer to it for the rest of your programming career. If you really don’t want to buy the big hardback, the second edition (and several hundred other books) is free on-line to ACM Student Members. I highly recommend that all CS majors become members of the ACM: at \$19/year, it’s an incredible bargain. The second edition is about 90% the same as the current third edition; I’ll try to have a copy of the third edition on reserve at the library.

The other textbook is Cliff Shaffer’s Data Structures and Algorithm Analysis (Dover 2012, ISBN 0486485811). You can buy a printed copy, but it’s also available free on-line from http://people.cs.vt.edu/~shaffer/Book/ (in either a Java or a C++ edition).

I may also give out other reading assignments by email, on the Web, or in journals.

This is a 3-credit class, which means you should budget 6 hours per week outside class for reading and homework. In particular, you’ll need to read about 30 pages per week, on average. Make time in your weekly schedule for this!

# Prerequisites

I assume that everyone in the class has passed CSC-MTH 156 (Discrete Structures) or an equivalent course covering Boolean logic and algebra, graphs and trees, and perhaps recurrence relations. I assume that you’ve passed pre-calculus: we’ll seldom need derivatives or integrals, but we’ll need logs and exponentials all the time, so refresh your memory of them. I also assume that everyone in the class has passed at least a year of programming courses. I don’t care much about the language, as long as you have written and debugged a number of programs and are familiar with the notions of algorithm, recursion, loop, array, linked list, etc. I’ll put up examples in Java or Scheme syntax, whichever seems more natural for the problem at hand.

There will probably be 5 homework assignments, each worth 12% of the semester grade, and a final exam worth 20%. Another 15% of your semester grade will be based on class participation and in-class presentations of homework problems; see below. The remaining 5% of your semester grade will be “brownie points”, which you earn by asking and answering good questions in class, coming to me for help when you need it, etc, and you lose by cheating, being a pain in class, etc.

The final exam must be taken at the scheduled time, unless arranged in advance or prevented by a documented medical or family emergency. If you have three or more exams scheduled on the same date, or a religious holiday that conflicts with an exam or assignment due date, please notify me in writing within the first two weeks of the semester in order to receive due consideration. Exams not taken without one of the above excuses will be recorded with a grade of 0.

# Late homework policy

Homework assignments will be accepted late, with a penalty of 25% per 24 hours or portion thereof after they’re due. An hour late is 25% off, 25 hours late is 50% off, etc. Any homework assignment turned in more than four days late will get a zero. Any homework assignment turned in after Dec 6 (the last day of class) will get a zero. (This is so I have, perhaps, time to grade them before the final exam.)

There will be several kinds of homework in this class. At one extreme are the analysis and “thought” problems on paper, resembling problems in a math class. At the other extreme are programming assignments, which may be written in any language that you and I both know and that runs at Adelphi (e.g. Scheme, Prolog, Java, C, C++). In between are pseudocode assignments: these need to be precise descriptions of an algorithm, like a computer program, but they don’t need to meet the syntactic requirements of a compiler (only a human being will read them) and you can ignore details that aren’t relevant to the problem at hand. For example, in a problem that wasn’t primarily about sorting, you might say “sort table A in increasing order by value” as one line of the algorithm. On the other hand, if the assignment were about sorting, I would expect you to give the details of your sorting algorithm.

Each student in the class will present some solutions to homework problems at the board in class, explaining the solution and answering technical questions from me and other students. (This is one reason I don’t want things handed in late: I’d rather see your solution rather than have you copy down and turn in the solution one of your classmates presented.) When I assign a problem, I’ll give it a number of “points” based on difficulty, and you are expected to present 20 “points” worth of problems in the semester. If you want to present a particular problem in class, try to get to class a few minutes early and start writing it up on the board. If you’re not sure of your solution or your presentation, feel free to discuss it with me in my office before the day you want to present it in class. Your grade for in-class presentations will be my assessment of how well you presented the solution and answered questions about it. I’ll also pay attention to who asks those questions.

# Attendance policy

I expect you to be in the classroom at 9:25, and to still be in the classroom at 10:40; if you’re not present, and miss some important material, it’s your problem. If you must miss a class, arrive late, or leave early, please let me know as far in advance as possible. I don’t explicitly grade on attendance, but consistent lateness or absence will impact the “brownie points” part of your grade.

# Students with Disabilities

If you have a disability that may impact your ability to carry out assigned course work, and are not enrolled in the Learning Disabilities Program, please contact the staff in the Disability Support Services Office (DSS), University Center, Room 310, (516) 877-3145. DSS@adelphi.edu. DSS will review your concerns and determine, with you, appropriate and necessary accommodations. All information and documentation of disability is confidential.

In particular, you may choose whether, and in how much detail, to discuss your disability with the instructor.

# Ethics

The Adelphi University Code of Ethics applies to this course; look it up on the Web at http://academics.adelphi.edu/policies/ethics.php.

Assignments in this class are to be done individually, or in teams of of two by prior permission; in the latter case, you may not do multiple homeworks with the same partner. You may discuss general approaches to a problem with classmates, but you may not copy large pieces of programs or homework solutions. If you do, all the students involved will be penalized (e.g. I’ll grade the assignment once and divide the points equally among the several people who turned it in).

All work on an exam must be entirely the work of the one person whose name is at the top of the page. If I have evidence that one student copied from another on an exam, both students will be penalized; see above.

# Student course evaluations

During the last two weeks of the class, you will be informed, via email and eCampus, that the University’s online course evaluation form is available for your input. It will no longer be available after the beginning of final-exam week, so make sure you fill it out before then. They don’t show me any of the results until after I’ve turned in semester grades. We really do take this stuff seriously in deciding what to do differently in future courses, so please give detailed feedback (something more specific and useful than “this course sucks!” or “this course rocks!”).

# Schedule

This class meets every Tuesday and Thursday from 9:25-10:40 AM in Hagedorn 111, unless we agree to change that. The schedule of topics, reading assignments, and homework assignments will be maintained on the Web at http://www.adelphi.edu/sbloch/class/343/calendar.html
The dates are subject to change depending on how classroom discussions actually go. I expect you to have read the reading assignments before the lecture that deals with that topic; this way I can concentrate my time on answering questions and clarifying subtle or difficult points in the textbook, rather than on reading the textbook to you, which will bore both of us. Please read ahead!