In this course you will learn the techniques and skills needed to solve algorithmic programming contests problems such as those that appear on the ICPC, Codeforces, DMOJ, and Topcoder. Most of your time will be spent writing programs on your own to solve problems.

Some students may go on to participate in the ECNA regional event, the ICPC North America Championship, and possibly even the ICPC World Finals. The date for the ECNA Regional is Saturday, February 26th 2022. The event will take place in person, probably in Cincinnati Ohio.

But the skills you will pick up from the course are far more valuable than just enabling you to win contests. Many of the algorithms and techniques are classic ones that every computer scientist should know. You will also learn to think about algorithms in a deeper way, because many of the problems require you have to devise a new algorithm, not just apply a classic one. You will also become highly fluent in a programming language of your choice. These skills will be of great value in your other classes, in your job interviews, and in your future work.

Basic Information

Weekly Problems

Rules and Academic Integrity

Grading

Logistics

Training Resources

Learning Material

Diversity, Equity and Inclusion

The regular weekly contests will take place Wednesdays from 7 to midnight in GHC 4307. Lectures may take place in the same classroom during the period 6-7pm before the contest. (The lectures are sporadic, so look for announements on Discord and Slack.) The lectures will cover introductory content aimed at beginners to competitive programming. Although attendance to the lectures is optional, it is strongly encouraged for beginners. During the contests, the instructor and the TA will be available for help in the classroom, or via Slack/Discord.

Instructor: Danny Sleator <sleator@cs.cmu.edu>, Phone: 412-268-7563

Teaching Assistants:

Chris Lambert <cslamber@andrew.cmu.edu>

Slack workspace: join link

Codeforces 15-295 Group: http://codeforces.com/group/KIrM1Owd8u/contests (Required)

Name List: Put your name, andrewID, and codeforces userID here(Required)

Grade Spreadsheet: View

Class Meetings: Wednesdays from 7:00 to 9:30pm, GHC 4307

For more information on how to join these groups, etc, see the Logistics section below.

Contest Link:Here

Problem StatementsHere

Solutions:For Editing For Viewing

Geometry! Love it or hate it! Geometry problems are often some of the most difficult problems that appear in programming competitions because they can be full of corner cases, precision, and rounding issues. This week, we will practice the fundamental techniques behind solving geometry problems.

Tutorial:Geometry tutorial

Contest Link:Here

Solutions:For Editing For Viewing

Contest Link:Here

Problem StatementsHere

Solutions:For Editing For Viewing

This week we will cover some advanced data structures that you won't find in your language's standard library. We'll learn to maintain disjoint sets under the union and find operation. We'll learn about lowest common ancestors in trees, and ranged minimum queries over arrays. It turns out that these two very different-sounding problems can actually be reduced to one another and hence we can use the same data structures to solve them. We'll also talk briefly about Euler-tours and Reachability trees. This contest was prepared by Soumyaditya Choudhuri (socho on Codeforces).

Tutorial:Union-Find

Tutorial:LCA and RMQ tutorial

Contest Link:Here

Solutions:For Editing For Viewing

This week we will practice string problems. Here are some notes about useful algorithms.

Rabin-Karp and Pattern Matching: Tutorial Recitation Notes

The KMP Algorithm

The Z Algorithm

Computing The Suffix Array and LCP Array

Contest Link:Here

Solutions:For Editing For Viewing

This week, we will explore even more graph algorithms. In particular, we will be looking at applications of maximum network flow. One key difference compared to prior weeks is that we will not actually focus on the algorithms for maximum flow (you should learn these in your algorithms courses), but rather on the applications. It is therefore crucial that you have a working implementation of a maximum flow algorithm ready to go before this week's contest begins. A maximum flow code is an important component of any competitive programmer's code library. If you have not learned a maximum flow algorithm before and can not implement one yourself, you are allowed to use a prewritten implementation by someone else. I will provide you with a sample C++ implementation that you are welcome to use. The first of the practice problems this week will help you check your implementation, as it simply asks you to compute a maximum flow in a graph, and not solve any particular application. It is strongly recommended that you do this to avoid getting wrong answers during the contest due to a bug in your flow code.

Lecture:VideoLecture:Video Slides

Sample code:C++

Lecture Notes:Basic Algorithms Advanced Algorithms Min-Cost-Flows

Contest Link:Here

Solutions:For Editing For Viewing

This week we will learn how to count things!

Tutorial:Counting tutorial

Contest Link:Here

Solutions:For Editing For Viewing

Contest Link:Here

Solutions:For Editing For Viewing

This week, we will continue the theme of graph algorithms and talk about shortest path problems in graphs. The fundamental algorithms that you will need to learn to solve these kinds of problems are breadth-first search (mentioned last time) and Dijkstra's algorithm. Other algorithms, such as Bellman-Ford and Floyd-Warshall are also very useful.

Lecture:Video Slides

Resources: Lecture notes on Bellman-Ford and Floyd-Warshall

Contest Link:Here

Solutions:For Editing For Viewing

This week we will talk about graph algorithms. This is a topic that will probably span multiple weeks as we cover things like shortest paths, minimum spanning trees, and network flows. For this week, we will focus on the fundamentals, and cover things like how to represent graphs and how to implement graph traversal algorithms (breadth first search and depth first search).

Lecture:Video DFS code in C++ BFS code in C++

Resources: Lecture notes on DFS and Strong Components

Contest Link:Here

Solutions:For Editing For Viewing

This week, we will practice the use of dynamic programming (DP) as a technique to solve
programming competition problems. DP is quite possibly the most frequently occuring
algorithmic technique used in competitions, with every ICPC contest always featuring
at least one, if not several problems that require it. Mastering this technique is key
to becoming a strong competitive programmer. DP revolves around two key concepts,
*optimal substructure*, which means that a problem can be solved by breaking it into
smaller versions of itself (much in the same way as divide and conquer), and
*memoization of overlapping subproblems*, which means to cache the solutions to
the smaller problems in case they need to be solved multiple times. Of all topics in
competitive programming, it probably requires the most practice in order to master, so get started!

Resources:451 Notes 1 451 Notes 2

Lecture Video:Here

Contest Link:Here

Solutions:For Editing For Viewing

This week, we will solve problems that use the *binary search* technique. You might think
of binary search as an algorithm for finding an element in a sorted list, but it is actually
a much more general technique than that, and can be used to solve a wide range of problems.
Essentially, binary search allows you to solve problems where you must minimize or maximize
some quantity subject to some contraint, as long as that constraint is monotone. A constraint
is monotone if it is true/false for all values of x up to some value, and then becomes false/true
after that value. Binary search allows us to efficiently find this partition point, and hence
solve the corresponding optimization problem. The practice problems this week should help you
to learn to apply this powerfull technique.

Lecture: Video binary search code ternary search code

Contest Link:Here

Solutions:For Editing For Viewing

This week, we will focus on the most commonly used and fundamental algorithms and data structures in competitive programming. We will review and practice using arrays, binary search trees, hashtables, and priority queues. Knowing and understanding how to use these data structures in your favourite programming language is crucial to being able to quickly implement solutions to problems. We will mainly use C++ to demonstrate, but the ideas should be applicable to any language that supports these data structures.

Lecture Video:Here

Contest Link:Here

Solutions:For Editing For Viewing

This week has no particular algorithmic theme. Instead, we will go over the basics of competitive programming and do our first contest on Codeforces. Please make sure you have a Codeforces account ready to go and understand how to upload your solutions to the problems. You should do some practice problems to get the hang of writing and submitting solutions to the Codeforces system.

We have created a practice contest to do just that. So go to this
page and (1) join
the group (right side) (2) register for the contest and (3) enter the
contest. Then you will find three problems you can try to solve. The
are: *Lights in the Morning*, *Deconstructed Password* and *Fine-tuned
Resistance*.

Practice Problems:Link

Contest Link:Here

Solutions:Here for editing Here for viewing

You can make use of generic on-line resources while solving problems.
These include things like language documentation, API documentation,
algorithm descriptions, terminology, etc. You *are allowed* to use
any code you have written, at any time in the past, for any purpose.
However, you *should not* search for or make use of code written by
others to solve the specific assigned problem. You're allowed to
copy somewhat standard pieces of code (e.g. a primality test) that
you find on-line or in a book.

So to summarize, each student should write his or her own code. If you're stuck on a problem, you are welcome to discuss it with another student in the class, or the course staff. But you cannot copy another student's code.

The violations described above are regarded as an academic integrity violation, and -- depending on the severity -- will result in penalties and/or be reported to the appropriate university authorities.

This course is 5 units. Each week you will be given several problems to try to solve during class. You will be allowed (for half credit) to solve these problems during the week after the contest ends. You can also get credit for solving problems during rated contests on Codeforces. (This site run rated contests approximately every two weeks.)

To be more specific, you can earn points from the following sources:

- Solving problems during the in-class contests. Each problem you solve is worth one point
- Solving problems from the in-class contests during the week following the contest. Each problem solved in this way is worth 0.5 points
- Solving problems during rated competitions on Codeforces. Division 3 contests and Problem A from Division 2 contests are not counted. You will earn one point for each problem solved.

The differences between 15-195 and 15-295 are: Students enrolled in 15-295 will not get credit for problems A and B of the weekly contests, but 15-195 students can. A student can take 15-195 only once, but 15-295 can be taken repeatedly.

Here is how your grade is determined:

score ≥ 25: A

score ≥ 15: B

score ≥ 10: C

score ≥ 5: D

- Everyone in the class and/or on any programming team should be in this Slack workspace: join link. This is one way we communicate with the class.
- Everybody participating should be in this google group: http://groups.google.com/group/15-295. I have added all registered students to the group. If you are not registered, let me know and I will add you to the group (email <sleator@cs.cmu.edu>).
- Everybody in the class is required to have a Codeforces account. We will be running our weekly contests on the Codeforces website via a mechanism called "mashups". If you do not already have an account on Codeforces, please create one. And add your name along with your Codeforces handle name to this spreadsheet. (It's the same one in Basic Information list above.)
- To join the 15-295 codeforces group, first create your codeforces account. Then go to this 15-295 Codeforces Group page. On this page you should see a list of the contests created for this course. After you've logged in with your codeforces account and clicked the link above to get to the group page, toward the right side of the page click on the link to join the group. (You only have to join once.) Then a "Register" link should appear next to the contest. Click on this link to register for the contest. After that another "Enter" link should be available for you to join the contest (if it has already started).
- As we proceed through the semester we will tabulate your results and put them into this grades document mentioned above.

First of all if you need help reading from standard input, or writing to standard output, see this link.

There are many online resources available for you to train with if you intend to become a serious competitive programmer. You can find thousands of practice problems for you practice and improve your skills. Some good places to find practice problems include:

- Codeforces: We use Codeforces for all of our in-class contests. On the Codeforces website, you can choose to solve individual problems from their old contests at your leisure, do a "virtual contest", in which you will be given a time limit to solve a set of problems from an old contest, or you can participate in real live contests roughly once per week.
- Topcoder: Topcoder also hosts live contests and allows you to practice on problems from their old contests. You need to install their Java applet in order to browse and solve problems, however.
- UVA Online Judge: UVA has a huge database of problems, many from past ICPC contests. A good website for finding particular problems to focus on is uHunt, which catalogues problems from UVA Online Judge into convenient categories for you to focus on (e.g. data structures problems, graph problems, string problems, etc.)
- SPOJ: SPOJ has a big database of practice problems that you can use. You can search for problems by tags to find ones that focus on a specific topic.
- CodeChef: Codechef has a number of practice problems that are categorized by difficulty, so you can work your way up from easy problems to hard problems as you progress. You can also search by tags to find problems that focus on specific topics.

If you are a beginner looking for resources to learn the various topics that appear in typical contests, some good sources are:

- E-Maxx Algorithms in English: This site contains well-written descriptions of hundreds of important algorithms, along with details on how to code them.
- Topcoder Competitive Programming Tutorials: A good selection of tutorials on standard problems appearing in contests.
- USACO Training Site: A training platform for the USA Computing Olympiad. It has a series of lessons with corresponding problems that are accessible to beginners and will make you a strong contest programmer.
- Competitive Programming by Halim & Halim: A popular book that covers the standard topics in competitive programming and includes a thorough catalogue of practice problems from UVA Online Judge (the uHunt website is based on this book). An updated version is coming out soon.
- Competitive Programmer's Handbook by Laaksonen: An ebook that covers most of the standard topics in competitive programming

*We must treat every individual with respect.* We are diverse in many
ways, and this diversity is fundamental to building and maintaining an
equitable and inclusive campus community. Diversity can refer to
multiple ways that we identify ourselves, including but not limited to
race, color, national origin, language, sex, disability, age, sexual
orientation, gender identity, religion, creed, ancestry, belief,
veteran status, or genetic information. Each of these diverse
identities, along with many others not mentioned here, shape the
perspectives our students, faculty, and staff bring to our campus. We,
at CMU, will work to promote diversity, equity and inclusion not only
because diversity fuels excellence and innovation, but because we want
to pursue justice. We acknowledge our imperfections while we also
fully commit to the work, inside and outside of our classrooms, of
building and sustaining a campus community that increasingly embraces
these core values.

Each of us is responsible for creating a safer, more inclusive environment.

Unfortunately, incidents of bias or discrimination do occur, whether intentional or unintentional. They contribute to creating an unwelcoming environment for individuals and groups at the university. Therefore, the university encourages anyone who experiences or observes unfair or hostile treatment on the basis of identity to speak out for justice and support, within the moment of the incident or after the incident has passed. Anyone can share these experiences using the following resources:

- Center for Student Diversity and Inclusion: <csdi@andrew.cmu.edu>, (412) 268-2150
- Report-It online anonymous reporting platform: reportit.net username: tartans password: plaid

All reports will be documented and deliberated to determine if there should be any following actions. Regardless of incident type, the university will use all shared experiences to transform our campus climate to be more equitable and just.

Danny Sleator Last modified: Wed Dec 1 21:49:57 2021