On February 24th starting at 11 AM Pacific Time, the 2023 ICPC Pacific Northwest Regional* will take place. This year, I will host the official contest broadcast, starting shortly before the beginning of the contest, on the ICPC Live YouTube channel.

The stream will cover the contest, discuss some problems and solutions, answer live questions from viewers, and maybe even include some surprise guests. We'll be streaming from the beautiful De Anza campus in San Jose, California, but this regional includes teams in on-site contests competing simultaneously on the same problems with the same scoreboard in:

• De Anza (California) [main site],
• UW Tacoma (Washinton),
• George Fox (Oregon),
• UBC (British Columbia), and
• BYUH (Hawaii)

If you're interested, you can see more info about the contest, the Division 1 Open Mirror, and the Division 2 Open Mirror.

Good luck, have fun to everyone who is competing tomorrow, and for everyone else, I hope to see you on the stream!

*: Not a typo; due to ongoing schedule difficulties resulting from COVID, the 2023 regional is being held in 2024.

Problem D of Codeforces Round #224 has incorrectly rendered samples for me. (Chrome on Mac). There are curly braces in the output for samples 2, 4, and 5. These are not in the actual data, they are just on the website.

Here is the second sample:

3 4
####
#>^{}#
####

The curly braces are not supposed to be there. I know there have since been updates to how samples are rendered (showing different backgrounds for adjacent test cases within the same sample, for example), so I suspect this may have broken in one of those updates.

Not sure where to post this, so thought I'd flag it here.

Meta Hacker Cup Finals 2023

The 2023 Meta Hacker Cup Finals will be happening this Saturday, starting at 6:00 AM Pacific.

We'll reveal the scoreboard and winner on a facebook livestream at 10:30 at 11:00. We'll include the stream on Codeforces if Codeforces decides to support Facebook livestreams, but otherwise, you'll want to visit facebook.com/hackercup to see the stream!

Good luck to the 25 finalists, we hope you enjoy the problems, and we hope everyone enjoys the livestream. You can also check out our teaser video before the contest!

Meta Hacker Cup Round 3

Good morning! Meta Hacker Cup Round 3 starts on Saturday, November 4th, 10 AM Pacific in under 14 hours! You're automatically registered for Round 3 if you placed in the top 500 of Round 2, or had a qualified bye from Round 1.

Important info:

• You'll qualify for the finals if you place in the top 25 in this round.
• If you place in the top 200 of this round, your T-shirt prize will have a Top-200 badge on the sleeve, unlike those who earned a shirt but were not in the top 200 in this round.
• The round will be 3 hours long.

You can find more info about T-Shirt details on this post. Good luck, have fun, and try not to get spooked by the problems!

Meta Hacker Cup Round 2

Good morning! Meta Hacker Cup Round 2 starts on Saturday, October 21st, 10 AM Pacific in under 26 hours! You're automatically registered for Round 2 if you scored at least 4 points in Round 1.

Important info:

• You'll qualify for Round 3 if you place in the top 500 in this round.
• If you place in the top 2000 of this round, you'll win a limited edition Hacker Cup t-shirt.
• If you qualify for Round 3, and you place in the top 200 of Round 3, your shirt will have a special "Top 200" badge on it.

You can find more info about T-Shirt details on this post. Good luck, have fun, and we'll see you on the scoreboard!

Meta Hacker Cup Shirts

Hacker Cup prizes are back this year, and the shirts are back in black! The top 2000 participants in Round 2 will win a shirt. If you qualify for Round 3 and finish in the top 200, you'll win a shirt with a top-200 badge on the sleeve instead of the normal shirt.

Just like last year, T-Shirts will be able to be claimed in your Hacker Cup Profile after we have finished plagiarism checks for the Round 3. (or after we have finished plagiarism checks for Round 2 if you didn't qualify for Round 3 and have no chance of winning a top-200 shirt)

You must claim your shirt by December 15th. We will not be shipping shirts after the 15th.

Due to regulations, Meta is also not able to support prize shipments to the following countries at this time:

Shirts shipped to addresses in the United States should be delivered within 1 week of being claimed. Shirts delivered to addresses outside the United States may take up to 3 weeks to be delivered.

Links to track your shipment can be found on your profile page once your shirt is shipped. Please note that you must have to claim your shirt from our vendor's website using the code in your profile. Their website looks like this:

Update: We'll release codes on your profile to all winners at the same time after we finish plagiarism checks for Round 3 on Monday, November 6th.

Update 2: Codes have been created and can be viewed on your profile.

Update 3: (November 22) Our stock for the following sizes is low. If you select one of these sizes, you will still get your shirt, but it won't be shipped until late December: XL, 3XL, Top-200 XL.

Meta Hacker Cup Round 1

Good morning! Meta Hacker Cup Round 1 starts on Saturday, October 7th at 10:00 AM Pacific in under 48 hours! Anyone can register for Round 1 this year, even if you haven't participated in the practice round.

Important info:

• To qualify for Round 2, you must solve at least one problem in this round. (Due to having too many submissions in the early part of the contest, we relaxed this requirement from the earlier one of needing to place in the top 5000 of the round)
• The contest will be 3 hours.
• As usual, you may not discuss solution ideas or code until after the contest hours is over. It's your responsibility to make sure that your code is not leaked. We'll DQ contestants if we have reason to believe they shared code or solutions with others.

Hacker Cup Round 2 Conflict with ICPC Regionals and WPC

Round 2 will overlap with some ICPC regionals and the World Puzzle Championship. For people able to prove that they will attend an official International Collegiate Programming Contest (ICPC) or World Puzzle Championship (WPC) during the day of the Round 2, it will be possible to get a bye from Round 2 and go directly to Round 3.

To get the bye you must attend one of the events during the day of Round 2 and finish in top 500 in Round 1. At most 50 contestants will get a bye; if more than 50 qualify, only the best 50 of them in Round 1 will qualify. To be considered for a bye, send an clarification request before Round 1 with the word "ICPC" or "WPC" followed by your name. We will later validate your status for the bye.

Prizes

T-shirts will be awarded to top participants based on performance in Rounds 2 and 3. Contestants who do not qualify for Round 2 cannot earn a prize. More prize details will be announced after Round 1.

We’ve put a lot of work into these problems, and we hope you enjoy the contest. Good luck, and see you on the scoreboard!

Meta Hacker Cup Practice Round

Good morning! The Meta Hacker Cup Practice Round starts in under 24 hours!

If you haven't yet, now's a great time to register for the round here. This round will be 72 hours long, starting tomorrow, September 21st at 10AM Pacific. Though it's optional, we strongly recommend participating. If you've never competed before, you'll see that Hacker Cup has a slightly unconventional submission system (you run your own code locally, and upload the output), so it's good to practice that. Be sure you have a sufficiently large stack size, for example, if you plan to use recursion in any of your solutions, and that you're familiar with compiling your code if you don't usually do that in other contests.

A couple other reminders before the contest starts:

• We ask that you don't discuss the statements or solutions (ideas or code) until after the practice round ends.
• If you choose to use an online compiler (such as IDEOne, or something else), it is your responsibility to make sure your code stays private. If your code becomes public, even by accident, you'll be DQ'd.
• If you're using Windows, don't use notepad because it sometimes may unexpectedly attempt to read some files as random Unicode characters.

If you're using an IDE, you may need to paste in larger inputs than you're used to. I recommend you do at least one of the following:

1. Make sure your IDE is capable of allowing you to paste in huge (up to like ~70mb) inputs, or better yet
2. Write your code to read from a file rather than stdin, or
3. Redirect stdin to a file when executing your code.

You can also view some of our FAQs here. Good luck, have fun, and see you on the scoreboard!

Meta Hacker Cup 2023 Schedule

Meta Hacker Cup is back! We’re excited to announce our schedule for our 2023 season, kicking off on September 22nd!

• Practice Round: Fri. Sept 22nd, 10am Pacific — Mon. Sep. 25th, 10am Pacific (72 hours)*
• Round 1: Sat. Oct. 7th, 10am — 1pm Pacific (3 hours)
• Round 2: Sat. Oct. 21th, 10am — 1pm Pacific (3 hours)
• Round 3: Sat. Nov. 4th, 10am — 1pm Pacific (3 hours)
• Finals: Sat. Dec. 9th, 6am — 10am Pacific (4 hours, Online)

*While optional, we recommend you participate in the Practice Round to familiarize yourself with our submission system before Round 1, when time will be at a premium.

To compete, you can register at Meta Coding Competitions at any time between now and September 25th.

You can expect familiar prizes including T-Shirts, Elite T-Shirts, and cash prizes for finalists. We’ll announce more prize details closer to Round 2.

We look forward to seeing you on the Practice Round’s scoreboard!

Llama Code in CP

Today, Meta released Llama Code, a Large Language Model trained specifically for code. It's trained on Python, C++, Java, PHP, Typescript, C#, Bash. They are releasing 3 models with 7B, 13B and 34B parameters respectively. The smaller two allow for Fill-in-the-Middle.

It's free for research and commercial use, but obviously requires a solid amount of computing power if you want to run it locally.

You can read more about it here: https://about.fb.com/news/2023/08/code-llama-ai-for-coding/

I'd be interested in seeing if this becomes useful in CP. It seems like there's a lot of potential, specifically with code completion with Fill-in-the-middle. Imagine having vscode, hitting "F3", typing something like "SegTree with lazy prop, range set max, and range +=", and getting exactly the segment tree you need in two seconds.

I also think it may be useful because although LLMs are currently horrendous at the problem solving aspect of CP (similarly to how tools like MidJourney suck at hands), if you can highlight an area or chunk of code and be like "hey, this part's bad, try again for just this part", that might help improve weaknesses.

Just a thought.

Fun Facts about NAC Teams

Are you or someone you know attending the North America Programming Camp? If so, we'd love to get some fun facts about the teams that are here!

Please submit your fun facts in this google form, or send them in a direct message to me, SecondThread on Codeforces!

What kind of facts are you looking for?

We're looking for anything exciting, interesting, or varied about your team that you're willing to share. Some great examples that we've seen in the past include:

• I play Smash Melee competitively in my free time
• One of our team members (his_handle) is getting married within a week of finals
• I'm surprisingly not actually a Computer Science major, instead I'm majoring in x and plan to use it for y.
• 2/3 of our team uses the non-C++ programming language X.
• This weird thing happened at regionals when we qualified.
• Our team practiced pretending to get questions wrong so that when we solved the last problem we didn't ruin the scoreboard reveal for anyone. One of our teammates really likes cycling and once biked over 100 miles in a single day.
• Last year, we were the highest-scoring team at the NAC not to make World Finals, by 27 minutes of penalty time
• Our team's mascot is X which we use for Y

Or really anything else that you think is unique or interesting.

What will these be used for?

Similarly to the 2022 NAC Stream, we'll use the content in these facts to make the stream more personal, and hype up your team when you submit a problem when we're watching the scoreboard. You can view the NAC stream here, and get contest updates here.

We're looking to get at least one fact per team. I'll be bothering you in person before the contest if you don't submit one, so might as well just make it easy on yourself and do it online now to avoid all potential human interactions later on, right? Just fill out this google form, or DM SecondThread!

Codeforces appears to have a minor bug in the backend regex evaluation for determining which submissions are legal java code. When attempting to submit, if you have an open curly brace in a submission before your outer class, you receive the following error:

Source should satisfy regex [^{}]*public\s+(final)?\s*class\s+(\w+).*

This happens even if the curly brace is in a comment. Here's an example case it won't let you submit when really it should:

/*
{
*/
public class A {
	public static void main(String[] args) {
	}
}

Here's the thing though: according to regex101 the regex is correct, and the above java code does indeed match (with PHP >=7.3 regex, the default). This makes me believe there's some bug in how CF is evaluating whether the regex matches, rather than with the regex itself.

Why it matters

Although it's not a super big deal, often times I will use a comment block above my main class as a note pad to think about the problem, and whenever I use curly braces in my notes, if I don't go back and delete them before submitting, CF doesn't accept the submission.

Alright, that's all. Happy debugging, and let me know if I can help :)

Meta Hacker Cup Finals

Good morning! The Meta Hacker Cup Finals are coming up in a few weeks, and will be held on December 10th. The contest will be 4 hours long, starting at 6:30 AM, PST, with a streamed scoreboard reveal at 11:00 AM, 30 minutes after the contest ends.

In the first ever Meta Hacker Cup Finals, the top 25 programmers of the over 16,000 entrants who competed in the first 4 rounds will battle it out on the hardest problem set of the season for a $20,000 grand prize. Contestants will have 4 hours to solve as many of programming challenges as they can of the 5 to 8 algorithmic tasks which will be revealed when the contest starts.

The scoreboard reveal will be streamed to the the Hacker Cup Facebook page, with commentary from SecondThread and Zef RosnBrick.

The 25 Finalists

*An individual's tourist factor is defined as the probability that this person would perform better than tourist in a Codeforces round, as predicted by the Elo Rating System.

Max Elo or Current Elo?

Here's a graph of all finalist's Round 3 place vs. their current elo and max elo. Although both current and max elo are useful predictors of performance in Hacker Cup, max elo has a higher R^2 coefficient, meaning it appears to be a better predictor.

See you in the Stream!

I'd like to draw a bit of attention to a blog I published last year asking for support for Facebook Livestreams on Codeforces. It looks like there was some initial interest in adding support for it, but it appears it isn't quite finished. If there's anything I can do to help make this happen, please reach out to me on CF DMs.

I hope to see you in the finals stream! We've had some great problems this year; perhaps you can find some of the ones you most liked or struggled with in the image below:

Update: The contest has started and the scoreboard can be viewed here: https://www.facebook.com/codingcompetitions/hacker-cup/2022/final-round/scoreboard

Fun Facts About World Finals Teams

Are you participating in ICPC World Finals in Dhaka this week? Is someone from your team competing in World Finals? Did your best friend's brother meet someone whose cousin competed in regionals against a team who qualified? If so, we'd love to get some fun facts about the world finals team from you!

If you have any, please submit your fun facts in this google form, or send them in a private message to me, SecondThread, on Codeforces!

What kind of facts are you looking for?

Well variety is what makes things exciting, so we don't want to limit it too much. But for some inspiration, some good ones we've seen in the past include:

• I play Smash Melee competitively in my free time
• One of our team members (his_handle) is getting married within a week of finals
• I'm surprisingly not actually a Computer Science major, instead I'm majoring in x and plan to use it for y.
• 2/3 of our team uses the non-C++ programming language X.
• This weird thing happened at regionals when we qualified.
• Our team practiced pretending to get questions wrong so that when we solved the last problem we didn't ruin the scoreboard reveal for anyone.
• One of our teammates really likes cycling and once biked over 100 miles in a single day.
• Last year, we were the highest-scoring team at the NAC not to make World Finals, by 27 minutes of penalty time
• Our team's mascot is X which we use for Y

Or really anything else that you think is unique or interesting.

What will these be used for?

I'll be commentating during the ICPCLive World Finals stream. Similarly to how we did this during the 2022 North American Championships Stream, we'll use the content in these facts to make the stream more personal, and hype up your team when you submit a problem when we're watching the scoreboard.

We're looking to get at least one fact per team. I'll be bothering you in person in Dhaka before the contest if you don't submit one, so might as well just make it easy on yourself and do it online now to avoid all potential human interactions later on, right? Just fill out this google form, or DM SecondThread!

Meta Hacker Cup Shirts

The Hacker Cup Team has done a bunch of work over the past year to streamline the shirt claiming process, and we're excited for you to finally see what we've added. You can now see the Hacker Cup Prizes you've earned in the past (and the ones available to claim this year) on your profile, with tracking codes, links to claim them, and your claim codes built into the site. Emails this year will also be coming from us, rather than from our third party, which should help prevent them from being marked as spam.

If you participated in Meta Hacker Cup this year and placed in the top 2000 of Round 2, you can now claim your shirt on your Hacker Cup profile page.

You must claim your shirt by November 18th. We will not be shipping shirts after the 18th.

Due to regulations, Meta is not able to support prize shipments to the following countries at this time:

Shirts shipped to addresses in the United States should be delivered within 3 business days of being claimed. Shirts delivered to addresses outside the United States may take up to 3 weeks to be delivered.

Links to track your shipment can be found on your profile page once your shirt is shipped. Please note that you must have to claim your shirt from our vendor's website using the code in your profile. Their website looks like this:

Update: Last week to claim shirts! You have until the 18th to claim your shirt and work out any claiming issues if you have not done so yet. After the 18th, we will need to focus on the Hacker Cup Finals, so we will no longer be delivering shirts for the 2022 season.

Update: 24 hours left to claim your shirt if you have not yet! Also, if the address you are shipping to is located in India, you may need to fill out your KYC documents on https://kyc.fedex.com.

Meta Hacker Cup Round 3

Good morning! Meta Hacker Cup Round 3 starts on Saturday, October 8th in under 48 hours! You're automatically registered for Round 3 if you placed in the top 500 of Round 2.

Important info:

• You'll qualify for the Hacker Cup Finals if you place in the top 25 in this round.
• If you place in the top 200 of this round, your Hacker Cup shirt will have a badge on the sleeve indicating you did so.
• The round will be 3 hours long.

Less important advice:

• Though we attempt to sort the problems in ascending order of difficulty and assign point values appropriately, we particularly encourage reading all the problems in this round.

A separate post about t-shirt distribution will be coming in the next few days. Good luck, have fun, and we'll see you on the scoreboard!

Days until contest: 4, 3, 2, 1, 0

Meta Hacker Cup Round 2 Editorial

Good morning!

As usual, written editorials are available in the solution section of all problems on the Hacker Cup site. Feel free to give problem feedback and discuss solutions here.

A1/A2: Perfectly Balanced

• Problem Statement, with written editorial
• Solution Video

B: Balance Sheet

• Problem Statement, with written editorial
• Solution Video

C: Balance Scale

• Problem Statement, with written editorial
• Solution Video

D1/D2: Work-Life Balance

• Problem Statement, with written editorial
• Solution Video

Feel free to leave your thoughts on the problems below. I hope you found the round, and the scoring distribution, almost perfectly balanced. :)

Meta Hacker Cup Round 2

Good morning! Meta Hacker Cup Round 2 starts on Saturday, September 24th in under 24 hours! You're automatically registered for Round 2 if you scored at least 15 points in Round 1.

Important info:

• You'll qualify for Round 3 if you place in the top 500 in this round.
• If you place in the top 2000 of this round, you'll win a limited edition Hacker Cup t-shirt.
• If you qualify for Round 3 as well, and you place in the top 200 of round 3, your shirt will have a special "Top 200" badge on it.

We put a lot of effort into these problems, so hope you'll find this contest as almost as balanced Codeforces Global Round 5. Good luck, have fun, and we'll see you on the scoreboard!

Update: Editorial

Meta Hacker Cup Round 1 Editorial

Good morning!

As usual, written editorials are available in the solution section of all problems on the Hacker Cup site. I thought this post might also be useful to see what people thought of the problems. After all, feedback is a gift, right?

A1/A2: Consecutive Cuts

• Problem Statement, with written editorial
• Solution Video

B1/B2: Watering Well

• Problem Statement, with written editorial
• Solution Video

C: Lemonade Life

• Problem Statement, with written editorial
• Solution Video

Feel free to leave your thoughts on the problems below :)

Meta Hacker Cup Round 1

Good morning! Meta Hacker Cup Round 1 starts on Saturday, September 10th in under 48 hours! You're automatically registered for Round 1 if you solved at least 1 problem in the qualification round.

Important info:

• You'll qualify for Round 2 if you score at least 15 points in this round.
• You won't know whether your submissions are correct or not until after the contest, so it may be wise to solve more problems than you need in case some of your submissions end up being incorrect. Just like in the qualification round, you'll be given validation data, but there may still be cases not in validation data which could trip you up.
• The round will last 24 hours, and you may use as much of that as you would like solving problems. As usual, you may not discuss solution ideas or code until after the 24 hours is over.

T-shirt winners will be decided in Round 2, with shirts with a special badge decided in Round 3. You'll need to pass this round to be eligible for winning a shirt or advancing to the final round.

We’ve put a lot of work into these problems, and we hope you enjoy the contest. Good luck, and see you on the scoreboard!

Update: Round starts in under 10 minutes, good luck!

Update #2: Editorial

Meta Hacker Cup Qualification Round Editorial

Good morning!

As usual, written editorials are available in the solution section of all problems on the Hacker Cup site. I thought this post might also be useful to see what people thought of the problems.

A: Second Hands

• Problem Statement, with written editorial
• Solution Video

B1/B2: Second Friend

• B1 Problem Statement, with written editorial
• B2 Problem Statement
• Moderately Entertaining Solution Video

C1/C2: Second Meaning

• C1 Problem Statement, with written editorial
• C2 Problem Statement
• Solution Video

D: Second Flight

• Problem Statement, with written editorial
• Solution Video

So, what'd you think of the problems?

Meta Hacker Cup Qualification Round

Good morning! The Meta Hacker Cup Qualification Round starts on Friday, August 26th in under 48 hours! If you haven’t yet, be sure to register on the Meta Coding Contests page.

Important info:

• In order to qualify for Round 1, you’ll need to solve at least one problem in this round.
• Once you've registered, you may wish to confirm that the information in your competition profile is up to date, including your display handle and which country you’d like to represent.
• In Hacker Cup, you run your own submissions on your computer, and upload your source code and the output of your source code to be graded. You’ll have 6 minutes to run your code locally and upload your solution, and whether you got the problem correct will be revealed at the end of the contest. Check out the FAQ for more details.

As a reminder, unlike some other multi-round coding contests, you may not share ideas or solutions about the problems with anyone until after the round has ended. We will be disqualifying contestants we believe to have participated illegitimately or shared their solutions or ideas online in any form before the end of the contest.

As usual, the 2022 season will have some great prizes, including 2,000 t-shirts, and cash prizes for all 25 finalists, including a $20,000 grand prize.

We’ve put a lot of work into these problems, and we hope you enjoy the contest. Good luck, and see you on the scoreboard!

Update: Editorial

Good morning everyone! The Hacker Cup team is excited to announce the schedule for our 2022 season, kicking off on August 26th! And for those of you who were wondering, yes–we’ve officially rebranded from Facebook Hacker Cup to Meta Hacker Cup.

• Qualification Round: Fri. Aug. 26th, 10am PDT — Mon. Aug. 29th, 10am PDT (72 hours)
• Round 1: Sat. Sept. 10th, 10am PDT — Sun. Sept. 11th, 10am PDT (24 hours)
• Round 2: Sat. Sept. 24th, 10am — 1pm PDT (3 hours)
• Round 3: Sat. Oct. 8th, 10am — 1pm PDT (3 hours)

To compete, you can register here at any time between now and the end of the qualification round on August 29th.

Stay tuned for more details about the finals, which are expected to happen at the end of 2022, likely in December.

We’ll provide more announcements as we get closer to the start of the season in August. Thanks, and we look forward to seeing you on the Qualification Round’s scoreboard!

ICPC North American Championships Livestream

Good morning! The North American Championship is happening this weekend in Orlando Florida, hosted by the University of Central Florida. The best ICPC teams from North America will be competing to qualify for the ICPC World Finals. Although ICPC won’t be producing a stream themselves, I’ll be creating an in-person stream. Featured guests:

• ecnerwala Andrew He, LGM and ICPC Gold Medalist
• Bill Poucher, ICPC Executive Director
• Dean Michael Georgiopoulos, UCF Dean of Computer Science
• TankEngineer Haobin Ni, IGM and ICPC Gold Medalist
• rpeng Richard Peng, Georgia Tech and North American Programming Camp Coach
• wphsucf Arup Guha UCF Coach
• Friggstad Zach Friggstad U Alberta and North American Programming Camp Coach
• Possibly some ICPC Judges, if permitting

The stream will start at 9:45 Florida time Monday, May 30th, or at this time for you.

We hope to see you there! If you know any of the teams or competitors and have interesting fun facts, you can submit them in this google form.

Thanks everyone for participating. Link to the stream

Good morning!

I just published a video about my performance (+173) on Global Round 20 and the past Div 1 Round. It's heavily edited, only includes highlights, and is definitely more entertaining than the usual screencasts, so I thought I'd post about it here. Go check it out.

Here's the thumbnail!

If you want to see me in the Top 10 Contributors so you don't have to go to my profile to check my color, you know what to do.