Table Of ContentAn Active Introduction to
Discrete Mathematics and Algorithms
Charles A. Cusack
[email protected]
David A. Santos
Version 2.5
December 21, 2015
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Copyright c 2015CharlesA.Cusack. Permissionisgrantedtocopy, distributeand/or
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modify this document under the terms of the GNU Free Documentation License,
Version 1.2 or any later version published by the Free Software Foundation; with no
Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy of the
license is included in the section entitled “GNU Free Documentation License”.
Copyright c 2007 David Anthony Santos. Permission is granted to copy, distribute
(cid:13)
and/or modify this document under the terms of the GNU Free Documentation Li-
cense, Version 1.2 or any later version published by the Free Software Foundation;
with no Invariant Sections, no Front-Cover Texts, and no Back-Cover Texts. A copy
of the license is included in the section entitled “GNU Free Documentation License”.
History
An Active Introduction to Discrete Mathematics and Algorithms, 2015, Charles A. Cusack.
•
Minor revisions. Algorithm Analysis chapter had major revisions.
An Active Introduction to Discrete Mathematics and Algorithms, 2014, Charles A. Cusack.
•
This is a significant revision of the 2013 version (thus the slight change in title).
An Introduction to Discrete Mathematics and Algorithms, 2013, Charles A. Cusack. This
•
document draws some content from each of the following.
– Discrete Mathematics Notes, 2008, David A. Santos.
– More Discrete Mathematics, 2007, David A. Santos.
– Number Theory for Mathematical Contests, 2007, David A. Santos.
– Linear Algebra Notes, 2008, David A. Santos.
– Precalculus, An Honours Course, 2008, David Santos.
These documents are all available from http://www.opensourcemath.org/books/santos/,
but the site appears not to be consistently available.
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Contents
Preface vii 7 Algorithm Analysis 195
7.1 Asymptotic Notation . . . . . . . . . . 195
How to use this book ix 7.1.1 The Notations . . . . . . . . . 195
7.1.2 Properties of the Notations . . 205
1 Motivation 1 7.1.3 Proofs using the definitions . . 209
1.1 Some Problems . . . . . . . . . . . . . 2 7.1.4 Proofs using limits . . . . . . . 214
7.2 Common Growth Rates . . . . . . . . 225
2 Proof Methods 7 7.3 Algorithm Analysis . . . . . . . . . . . 233
2.1 Direct Proofs . . . . . . . . . . . . . . 7 7.3.1 Common Time Complexities . 253
2.2 Implication and Its Friends . . . . . . 16 7.4 Problems . . . . . . . . . . . . . . . . 258
2.3 Proof by Contradiction. . . . . . . . . 20
2.4 Proof by Contraposition . . . . . . . . 29 8 Recursion, Recurrences, and Mathe-
matical Induction 263
2.5 Other Proof Techniques . . . . . . . . 31
8.1 Mathematical Induction . . . . . . . . 263
2.6 If and Only If Proofs . . . . . . . . . . 33
8.1.1 The Basics . . . . . . . . . . . 264
2.7 Common Errors in Proofs . . . . . . . 35
8.1.2 Equalities/Inequalities . . . . . 269
2.8 More Practice . . . . . . . . . . . . . . 38
8.1.3 Variations . . . . . . . . . . . . 272
2.9 Problems . . . . . . . . . . . . . . . . 42
8.1.4 Strong Induction . . . . . . . . 276
8.1.5 Induction Errors . . . . . . . . 278
3 Programming Fundamentals and Algo-
8.1.6 Summary/Tips . . . . . . . . . 280
rithms 45
8.2 Recursion . . . . . . . . . . . . . . . . 283
3.1 Algorithms . . . . . . . . . . . . . . . 45
8.3 Solving Recurrence Relations . . . . . 291
3.2 The mod operator and Integer Division 49
8.3.1 Substitution Method . . . . . . 293
3.3 If-then-elseStatements . . . . . . . 56
8.3.2 Iteration Method . . . . . . . . 297
3.4 The for loop . . . . . . . . . . . . . . 58
8.3.3 Master Theorem . . . . . . . . 305
3.5 Arrays . . . . . . . . . . . . . . . . . . 61 8.3.4 Linear Recurrence Relations . . 307
3.6 The while loop . . . . . . . . . . . . . 65 8.4 Analyzing Recursive Algorithms . . . 311
3.7 Problems . . . . . . . . . . . . . . . . 68 8.4.1 Analyzing Quicksort . . . . . . 315
8.5 Problems . . . . . . . . . . . . . . . . 319
4 Logic 71
4.1 Propositional Logic . . . . . . . . . . . 71 9 Counting 323
4.1.1 Compound Propositions . . . . 73 9.1 The Multiplication and Sum Rules . . 323
4.1.2 Truth Tables . . . . . . . . . . 80 9.2 Pigeonhole Principle . . . . . . . . . . 328
4.1.3 Precedence Rules . . . . . . . . 82 9.3 Permutations and Combinations . . . 334
9.3.1 Permutationswithout Repeti-
4.2 Propositional Equivalence . . . . . . . 84
tions . . . . . . . . . . . . . . . 334
4.3 Predicates and Quantifiers . . . . . . . 96
9.3.2 Permutations with Repetitions 337
4.4 Normal Forms. . . . . . . . . . . . . . 105
9.3.3 CombinationswithoutRepeti-
4.5 Bitwise Operations . . . . . . . . . . . 108
tions . . . . . . . . . . . . . . . 341
4.6 Problems . . . . . . . . . . . . . . . . 111
9.3.4 Combinations with Repetitions 347
9.4 Binomial Theorem . . . . . . . . . . . 351
5 Sets, Functions, and Relations 117
9.5 Inclusion-Exclusion . . . . . . . . . . . 354
5.1 Sets . . . . . . . . . . . . . . . . . . . 117
9.6 Problems . . . . . . . . . . . . . . . . 360
5.2 Set Operations . . . . . . . . . . . . . 123
5.3 Functions . . . . . . . . . . . . . . . . 134 10 Graph Theory 365
5.4 Partitions and Equivalence Relations . 145 10.1 Types of Graphs . . . . . . . . . . . . 365
5.5 Problems . . . . . . . . . . . . . . . . 159 10.2 Graph Terminology . . . . . . . . . . . 369
10.3 Some Special Graphs . . . . . . . . . . 374
6 Sequences and Summations 163 10.4 Handshaking Lemma . . . . . . . . . . 377
6.1 Sequences . . . . . . . . . . . . . . . . 163 10.5 Graph Representation . . . . . . . . . 379
6.2 Sums and Products . . . . . . . . . . . 176 10.6 Problem Solving with Graphs . . . . . 380
6.3 Problems . . . . . . . . . . . . . . . . 192 10.7 Traversability . . . . . . . . . . . . . . 383
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10.8 Planarity . . . . . . . . . . . . . . . . 385 GNU Free Documentation License 437
10.9 Problems . . . . . . . . . . . . . . . . 387
11 Selected Solutions 389 Index 441
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Preface
This book is an attempt to present some of the most important discrete mathematics concepts to
computer science students in the context of algorithms. I wrote it for use as a textbook for half
of a course on discrete mathematics and algorithms.
Someofthematerialisdrawnfromseveralopen-sourcebooksbyDavidSantos. Othermaterial
is from handouts I have written and used over the years. I have extensively edited the material
from both sources, both for clarity and to emphasize the connections between the material and
algorithms where possible. I have also added a significant amount of new material. The format
of the material is also significantly different than it was in the original sources.
I should mention that I never met David Santos, who apparently died in 2011. I stumbled
upon his books in the summer of 2013 when I was searching for a discrete mathematics book to
use in a new course. When I discovered that I could adapt his material for my own use, I decided
to do so. Since clearly he has no knowledge of this book, he bears no responsibility for any of the
edited content. Any errors or omissions are therefore mine.
This is still a work in progress, so I appreciate any feedback you have. Please send any typos,
formatting errors, other errors, suggestions, etc., to [email protected].
I would like to thank the following people for submitting feedback/errata (listed in no par-
ticular order): Dan Zingaro, Mike Jipping, Steve Ratering, Victoria Gonda, Nathan Vance, Cole
Watson, Kalli Crandell, John Dood, Coty Franklin, Kyle Magnuson, and Katie Brudos.
Charles A. Cusack
July, 2014
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How to use this book
As the title of the book indicates, this is not a book that is just to be read. It was written so
that the reader interacts with the material. If you attempt to just read what is written and take
no part in the exercises that are embedded throughout, you will likely get very little out of it.
Learning needs to be active, not passive. The more active you are as you ‘read’ the book, the
more you will get out of it. That will translate to better learning. And it will also translate to a
higher grade. So whether you are motivated by learning (which is my hope) or merely by getting
a certain grade, your path will be the same–use this book as described below.
The content is presented in the following manner. First, concepts and definitions are given–
generally one at a time. Then one or more examples that illustrate the concept/definition will
be given. After that you will find one or more exercises of various kinds. This is where this
book differs from most. Instead of piling on more examples that you merely read and think you
understand, you will be asked to solve some for yourself so that you can be more confident that
you really do understand.
Some of the exercises are just called Exercises. They are very similar to the examples, except
that you have to provide the solution. There are also Fill in the details which provide part of
the solution, but ask you to provide some of the details. The point of these is to help you think
aboutsome of the finerdetails that you might otherwise miss. Thereare also Questionsof various
kinds that get you thinking about the concepts. Finally, there are Evaluate exercises. These ask
you to look at solutions written by others and determine whether or not they are correct. More
precisely, your goal is to try to find as many errors in the solutions as you can. Usually there will
be one or more errors in each solution, but occasionally a correct solution will be given, so pay
careful attention to every detail. The point of these exercises is to help you see mistakes before
you make them. Many of these exercises are based on solutions from previous students, so they
often represent the common mistakes students make. Hopefully if you see someone else make
these mistakes, you will be less likely to make them yourself.
The point of the exercises is to get you thinking about and interacting with the material. As
you encounter these, you shouldwrite your solution inthe space provided. After you have written
your solution, you shouldcheck youranswer withthesolution provided. You willget themostout
of them if you first do your best to give a complete solution on your own, and then always check
your solution with the one provided to make sure you did it correctly. If yours is significantly
different, make sure you determine whether or not the differences are just a matter of choice or if
there is something wrong with your solution.
Ifyougetstuckonanexercise, youshouldre-readthepreviousmaterial(definitions,examples,
etc.) and see if that helps. Then give it a little more thought. For Fill in the details questions,
sometimes reading what is past a blank will help you figure out what to put there. If you get
really stuck on an exercise, look up the solution and make sure you fully understand it. But don’t
jump to the solution too quickly or too often without giving an honest attempt at solving the
exercise yourself. When you do end up looking up a solution, you should always try to rewrite
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it in the space provided in your own words. You should not just copy it word for word. You
won’t learn as much if you do that. Instead, do your best to fully understand the solution. Then,
without looking at the solution, try to re-solve the problem and write your solution in the space
provided. Then check the solution again to make sure you got it right.
It is highly recommended that you act as your own grader when you check your solutions.
If your solution is correct, put a big check mark in the margin. If there are just a few errors,
use a different colored writing utensil to mark and fix your errors. If your solution is way off,
cross it out (just put a big ‘X’ through it) and write out your second attempt, using a separate
sheet of paper if necessary. If you couldn’t get very far without reading the solution, you should
somehow indicate that. So that you can track your errors, I highly recommend crossing out
incorrect solutions (or portions of solutions) instead of erasing them. Doing this will also allow
you to look back and determine how well you did as you were working through each chapter. It
may also help you determine how to spend your time as you study for exams. This whole process
will help you become better at evaluating your own work. This is important because you should
be confident in your answers, but only when they are correct. Grading yourself will help you gain
confidence whenyou are correct and help you quickly realize whenyou are not correct sothat you
do not become confident about the wrong things. Another reason that grading your solutions is
important is so that when you go back to re-read any portion of the book, you will know whether
or not what you wrote was correct.
It is important that you read the solutions to the exercises after you attempt them, even if
you think your solution is correct. The solutions often provide further insight into the material
and should be regarded as part of any reading assignment given.
Make sure you read carefully. When you come upon an Evaluate exercise, do not mistake it
for an example. Doing so might lead you down the wrong path. Never consider the content of an
Evaluate exercise to be correct unless you have verified with the solution that it is really correct.
To be safe, when re-reading, always assume that the Evaluate exercises are incorrect, and never
use them as a model for your own problem solving. To help you, we have tried to differentiate
these from other example and exercise types by using a different font.
Finally, there is an expectation that you are able to solve every exercise on your own. (Note
that I am talking about the exercises embedded into the chapters, not the homework problems
at the end of each chapter.) If there are exercises that you are unable to complete, you need to
get them cleared up immediately. This might mean asking about them in class, going to see the
professor or a teaching assistant, and/or going to a help center/tutor. Whatever it takes, make
sure you have a clear understanding of how to solve all of them.
