Hi DMOJ!

Dr. Daniel Zingaro "yeerk16" of the University of Toronto has recently been working on a book introducing contest programming concepts in a practical way. It's nearing completion, so we thought we'd let you know! I'll let Dr. Zingaro handle the introduction:

Programming is about using a computer to solve problems, and algorithms and data structures are the building blocks of computer programs. For each problem that a programmer wants to solve, they employ an algorithm: a sequence of steps for solving the problem. Many books teach algorithms independently of specific problems, but this book uses careful explanations, examples, and arguments, rather than formal mathematics and proofs which make it difficult for you to connect what you are learning to what you can do with that learning. Algorithmic Thinking: A Problem-Based Introduction teaches you to use the best algorithms and data structures for a given situation by walking you through solving problems pulled from international programming competitions, such as how to determine whether snowflakes are unique; how to win a game in the minimum number of moves; how to find the number of ways to get to someone's house; how to escape a cave in as few steps as possible; and so on.

You'll tackle challenging topics like recursion, dynamic programming, graphs, greedy algorithms, heaps, hash tables, segment trees, and other data structures for efficiently handling data. The book contains no pseudocode: all code is written in C and is thoroughly explained in the text (C is a de facto programming language for programming competitions). By the end of the book, you should understand the importance of carefully working through a problem, and why it pays to organize data using data structures.

Algorithmic Thinking: A Problem-Based Introduction will be out in print in October, but it's available as an Early Access ebook now. Chapters will become available as soon as they're copyedited; the first four chapters are available now (including a free first chapter), and the rest will follow in a few weeks.

The book uses problems from various online judges (including DMOJ!) as exercises, which sounds like a fun, hands-on way to pick up new tricks.

We're also excited to give away some copies in future DMOJ competitions, so watch out for that :)

Thanks for participating in the DMOPC '19 April Contest!

Congratulations to the top 5 contestants!

1. bqi343 (perfect score)
2. 300iq (perfect score)
3. bruce
4. zhouzixiang2004
5. Eliden

We hope you enjoyed the contest!

From Monday, May 4th to Wednesday, May 6th, we'll be hosting the April* DMOJ Monthly Open Programming Contest!

Anyone with a DMOJ account is welcome to participate, and anyone without one is welcome to register and participate.

Contestants may participate in any 4-hour window between 09:00 EDT of May 4th and 23:59:00 EDT of May 6th. Please see the contest page for more details.

See you soon!

*We cannot guarantee the existence of April in this contest. We apologize in advance for any month related bamboozling.

From April 26th to April 28th, we'll be hosting Wesley's Anger Contest 4! With the CCO quickly approaching, this contest will be a great way to practice your problem solving skills. The difficulty of the problems will be similar to a typical Wesley's Anger Contest. In addition, Zeyu, Pookmeister, and aeternalis1 decided to make all the problems squirrel themed!

Anyone with a DMOJ account is welcome to participate, and anyone without one is welcome to register and participate.

Contestants may participate in any 4-hour window between April 26th, 09:00 EDT to April 28th, 23:59 EDT. Please see the contest page for more details.

Good luck to all the participants!

From Friday, April 17th to Sunday, April 19th, we will be hosting the first ever Art Academy contest!

Contestants may participate in any 3-hour window between 0:00 EDT of April 17th and 23:59:00 EDT of April. 19th. Feel free to view the contest page for more details.

Hope to see you there, and best of luck!

It's been a while since we've posted an update on what we've been working on, so we felt it was about time for one.

New Baremetal Judges

The biggest news we have to share is already over a month old by now: DMOJ judges now run on a dedicated, bare-metal machine!

Until now we've sourced our judges from cloud providers, but that has always been a bit of hardware roulette: sometimes a judge VM would be provisioned on Intel hardware, while other times our provider would give us shiny new AMD EPYC cores. Typically, these machines were also overcommitted by our hosts, so timing consistency between submissions was at the mercy of potentially noisy neighbours.

No longer! We've gone and purchased real hardware to run judges on: a 6-core (12-thread) AMD Ryzen 5 3600X @ 3.8 GHz, with 16 GB 3200 MHz CL16 dual-channel RAM. Frequency scaling has been disabled for timing consistency. Each judge runs in a QEMU instance allocated 2 GB RAM and 1 physical core (2 threads).

These judges are much (2-5×) faster than the old ones (and empirically, much more consistent). As a result, problem time limits have been rescaled based off a randomized sample of submissions — some problems may currently have time limits that are either too low, or too high. If you think you've run into such a problem, please let us know in Slack.

New Runtime Versions

We maintain Docker images based off stable Debian (Buster) with runtimes as part of the DMOJ/runtimes-docker project; these are the runtimes used by judges on the DMOJ. Since the GCC in Buster (version 8) was incorrectly identifying the Zen 2 judges as Bulldozer, we've upgraded our images to Debian Sid in order to get GCC 9. Apart for better support for our judges, you can read what's new here.

As a side-effect of upgrading to Sid, we now have much newer versions of most runtimes.

Notably, Python 3 has been upgraded from 3.7 to 3.8, and Clang from 7 to 9. OCaml was also upgraded from 4.05 to 4.10; we took this opportunity to rewrite the OCaml backend to link Jane Street Core/Base/Stdio and Zarith libraries, for a nicer functional programming experience :)

Thanks for participating in the DMOPC '19 March contest!

Congratulations to the top 5 contestants!

1. ecnerwal (perfect score)
2. bqi343 (perfect score)
3. 300iq
4. zhouzixiang2004
5. zxyl

We hope you enjoyed the contest, and we look forward to seeing you in DMOPC '19 April! (Typically, DMOJ doesn't host an April DMOPC as DMPG is hosted at that time instead. However, given the circumstances at the moment, it's not possible for DMPG to run, so we are planning on hosting another DMOPC.)

From Friday, March 27th to Sunday, March 29th, we'll be hosting the March DMOJ Monthly Open Programming Contest!

Anyone with a DMOJ account is welcome to participate, and anyone without one is welcome to register and participate.

Contestants may participate in any 3-hour window between 09:00 EDT of Mar. 27th and 23:59:00 EDT of Mar. 29th. Please see the contest page for more details.

See you soon!

Thanks for participating in the DMOPC '19 February contest!

Congratulations to the top 5 contestants!

1. bqi343 (perfect score)
2. zhouzixiang2004 (perfect score)
3. Egor (perfect score)
4. d (perfect score)
5. Eliden (perfect score)

We hope you enjoyed the contest, and we look forward to seeing you in DMOPC '19 March!

From Friday, February 28th to Sunday, March 1st, we'll be hosting the February DMOJ Monthly Open Programming Contest!

Anyone with a DMOJ account is welcome to participate, and anyone without one is welcome to register and participate.

Contestants may participate in any 3-hour window between 0:00 EST of Feb. 28th and 23:59:00 EST of Mar. 1st. Please see the contest page for more details.

See you soon!

Hello DMOJ! We are excited to host the new Victor’s Programming Exhibition (VPEX)! The contest will take place during a 2.5-hour window between 3:00 pm EST of Feb. 7th, 2020 to 3:00 pm EST of Feb. 10th, 2020. To help you prepare for the CCC, this contest will feature 6 problems with an approximate difficulty ranging from CCC Junior 1 to CCC Senior 5. This contest will not be rated.

VPEX Onsite

While everyone is welcome to participate online, we also invite you to attend VPEX on-site at Victoria Park CI, free of charge! The on-site contest is identical to its online counterpart, except for the following additions:

• The contest conditions will be more realistic.
• Solutions will be explained at the end of the contest.
• Prizes, food, and provisions will be provided to each participant.

Victoria Park CI is located at 15 Wallingford Rd, North York, ON M3A 2V1.

Directions to the contest location can be found here. The on-site contest will take place from 3:00 to 6:00 pm on Feb. 7th, although you may leave early if you are done. Please arrive between 3:00 and 4:00 pm.

Credits

The problem setter for this contest is Aaeria.

The testers are magicalsoup, Bobliu, crackersamdjam, and Arihan10.

From February 1st to February 3rd, we'll be hosting Wesley's Anger Contest 3! With the CCC quickly approaching, this contest will be a great way to practice your problem solving skills. The difficulty will be easier than the previous two contests in this series.

Anyone with a DMOJ account is welcome to participate, and anyone without one is welcome to register and participate.

Contestants may participate in any 3-hour window between February 1st, 1:00 PM to February 3rd, 11:59 PM. Please see the contest page for more details.

Good luck to all the participants!