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.

Geothermal just got passed 3000 rating after round #783, making him the 5th American LGM (as of when ratings update). This came with a very clutch 1:59:56 solve on problem D, making it even more impressive. He's been a personal friend of mine since we met at an in-person contest in Texas that I drove 17 hours to go to back when he was still purple I believe, so it's great to see him reach this achievement. Well done, Jay, you've earned it.

I've create a private Codeforces mashup and would like to disable manager mode and submit solutions to the ongoing mashup as a contestant. I'm trying to click this button:

Instead of disabling manager mode as expected, Codeforces just refreshes the page, and I stay in manager mode. If it's helpful for debugging, here's a video of it happening.

If I'm using the tool incorrectly (or my account is in an invalid state or something), A) what am I doing wrong, and B) IMO, I think it would be helpful if CF displays an error message or something telling me what the problem is rather than just silently failing.

Good morning! AlphaCode, Google's AI to compete in programming contests, has done some pretty awesome stuff. The engineers who made it also wrote a whitepaper which you can read here. If, like me, you prefer to have it explained to you by somebody else who has already done the reading for you, I made a video explaining what I feel are the important parts.

Anyway, I hope you enjoy the video. As usual, questions, comments, and good mornings are always welcome :)

Good morning!

If you earned a shirt in Facebook Hacker Cup 2021 by placing in the top 2000 of Round 2 and did not yet get an email with a code to claim your shirt, please DM me on CF with the following information:

1. Your place in Hacker Cup Round 2 in 2021 (such as 1999th place)
2. A link to your facebook account (such as https://www.facebook.com/profile.php?id=100008893002051 )
3. The email address linked to your facebook account (such as [email protected])

Pi day, 2022, (March 14th, 2022) will be the last day that we ship 2021 shirts. For the 25 finalists, prizes are handled separately, and you can contact us individually.

Focus is a Virtue

I know current geopolitical events are on the top of a lot of people's minds at the moment. I wish for those involved the safety of their families, land, and heritage. I truly don't mean for this to come off as insincere, insensitive, or trying to diminish the importance of these events to people's personal lives.

But that being said...

Codeforces isn't the place for such debates and politics. I'm not saying these discussions don't need to happen. They do. But them happening on this surface is essentially well-intentioned spam. In particular, beyond the fact that Eastern Europeans and Russians are disproportionately good at competitive programming, this has really nothing to do with competitive programming, with the interests of this community, or with a competitive programming website.

This stuff belongs on social media, or places like Reddit and Discord. Or if, for whatever reason, we feel it really has to happen here, can we please at least keep it to one post, rather than half of the recent actions?

Alright, I've spoken my peace, bring on the flood of downvotes...

Context

Codeforces currently supports embedded Youtube and Twitch livestreams. Hacker Cup Finals is streamed only to Facebook, but I imagine there are lots of people who would like to watch it [or at least would like to know about it] on Codeforces. Unfortunately, it seems unlikely that Hacker Cup would be streamed to Youtube or Twitch in the foreseeable future.

Implementation?

It looks like embedding the stream is as simple as using an iframe, from the little research that I've done on this page, which is about a church for some reason.

I don't know how Codeforces implements this integration, but if it is with an iframe, it might be as simple as a third case to the supported stream link regex.

Why should Codeforces want to add Facebook Livestream support?

Because Hacker Cup is a big-name programming contest. If Codeforces wants to continue to be the place for everything competitive programming related, it would be good to support at least the major CodeJam Finals/Hacker Cup Finals/ICPC World Finals streams, since most competitive programmers are interested in them.

The direct payoff from Codeforces's perspective is that it's support for a major contest and something very beneficial to it's users. The payoff from Hacker Cup's perspective to use this feature is that it provides greater visibility and integration with the community of people who are interested in programming contests. It's clear that there's a huge overlap in Hacker Cup contestants and CF users.

What do you think? Would you like to watch the Hacker Cup Finals stream here?

Good Morning! I'm no Laggy, but I thought I would continue the tradition of making a "Teams" list for the 2021 Facebook Hacker Cup Finals, since I always found the ICPC World Finals lists fun. So here goes!

Facebook Hacker Cup 2021 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.

**Contestants with question marks in their country have not told us which country you wish to represent, and this is my best guess based on your Codeforces profile.

Does CF Rating Predict Hacker Cup Performance?

Here's a graph of the finalists' rating vs. their Round 3 place:

So yes, it's a good predictor, but it certainly doesn't explain everything; it's not out of the question that any competitor could have an unusually good or bad contest, as you would expect.

Post-Contest Livestream (on Facebook)

Yep, be sure not to miss all the excitement in the post-contest livestream, during which Zef and I reveal the final scoreboard! Get excited--I'll see you Saturday!

Good morning! ICPC World Finals just concluded in Moscow. I was lucky enough to be participate representing the University of Central Florida, who finished in a respectable 17th place.

While there, friends, acquaintances, and CF Legends signed my Codeforces sweatshirt in their handle with their current color. The most common request of the people I asked was to show off what it ended up looking like on a blog post of Codeforces, so here that is!

Signers:

• MikeMirzayanov the creator and maintainer of Codeforces and Polygon who deserves our eternal thanks, and Una_Shem without whose work there would be no sweatshirt to sign.
• tourist the legend and best competitive programmer of all time
• Petr the legend and programming philosopher
• Um_nik, KAN, and Ekler* the 2021 ICPC World Finals Champions, (who signed before being such champions), and their coaches vepifanov and ashmelev
• Golovanov399, AndreySergunin, amethyst0 gold medalists from the host university MIPT
• Monogon the contribution overlord whom you should upvote, and his teammate richzli from Perdue
• Benq, sqrtdecompton, and C_SUNSHINE from MIT, with their coach jcvb
• andrewzta legendary coach of ITMO and author of all ASC sets
• davidberard, .rem, ehnryx, from UBC and their coaches zhed and inutard
• RobeZH my friend with whom I had a friendly wager with to race to IGM, and his teammates top34051 and LUL____SEPLED1305* from Wisconsin Madison
• bicsi from the University of Bucharest who came in with the clutch sign 10 minutes before I left
• kpw29**, _h_, and zdolna_kaczka from Cambridge, the most obnoxious competitors I have met in my life
• miagkov** my friend from Stanford who competed against me at unofficial in-person NAP Camp, and his teammate andyshih12**
• brunomont who I've discussed some CF blogs with and his teammate Paniago who appears to have misspelled his own name
• tbuzzelli my friend and Google CodeJam contributor
• TheOneYouWant representing the Indian Institute of Technology, Bombay
• SecondThread me, my teammates Harpae and Xylenox, and my coach wphsucf

Thanks to everyone for signing it! I hope you all had a great time at World Finals, and I'll see you on the scoreboard on the next Codeforces Rounds! It was great to finally meet so many people who I've only seen virtually before in person. If you have any fun pictures from WF that you're itching to share, the comments below are always open.

I started thinking about this during my livestream of the solution to round 731, and discussed this in a comment a bit earlier, but it seems novel enough and might require enough debate that I thought it makes sense to be it's own blog post:

Suppose I have an array $$$a$$$ of $$$n$$$ integers, each up to a million. What is the worst-case runtime of the following code?

int gcd(int a, int b) {
   return b==0?a:gcd(b, a%b);
}

//in main
int gcd=a[0];
for (int i:a) gcd=gcd(i, gcd);

Conventionally, I have always thought it was $$$n*log(MAXVAL)$$$. However, each time the gcd call runs, the answer decreases by an expected factor of about 1.6 (the golden ratio). But really, we only do all $$$log(n)$$$ calls if the gcd gets quite small. In that case, future gcd calls will be $$$O(1)$$$, not $$$O(log)$$$. So do we have a clean potential function like: the number of prime factors in gcd, which can bound the total GCD recursion? I know that this is some very hand-wavey logic, but it seems almost legit enough for me to believe it. Or is this totally not true? I'm secretly wishing it's true because it would be cool, but also I feel like I would have seen this before if it was both commonly known and true.

TLDR: is the above code really $$$O(n + log(MAXVAL))$$$, instead of $$$O(n * log(MAXVAL))$$$?

Good morning everyone!

After the tremendous popularity of our first article, the CF Hot News team is back! This time, we have just come across some irrefutable evidence of hidden operations involving the ICPC 2021 World Finals, provided to us by several top-secret CF sources.

We sincerely hope that these insights can be helpful to all competators optimize their training in the coming months to optimally prepare for the contest.

Please enjoy: https://youtu.be/Xf8DwlipmG4

What other top secret revelations lie undiscovered? I bet the comments will tell us...

SecondThread vs. galen_colin Lockout Duel (ft. neal, stevenkplus)

Good morning everyone!

There are three great unsolved questions on Codeforces that every pupil dreams to one day know the answer to:

• What's the best opening move when playing the Epsilon Guessing Game against a geometry problem?
• How many cyans is Um_nik worth, modulo $$$10^9+7$$$?
• Who is really the 229th best programmer on Codeforces: SecondThread or galen_colin?

While we may never know the answer to the first two, Colin and I will settle the third question once and for all this Sunday in a 1v1 duel! Don't miss it!

Join us at this time on Sunday where we will compete head-to-head in a 1v1 lockout at https://www.twitch.tv/nealwu, with live commentary from neal!

Update: stevenkplus, the initiator of the first Lockout grudge match, will be co-commentating as well! Woohoo!

Update: YouTube video of the duel is posted: https://www.youtube.com/watch?v=WCqs6hbTMJY. Now includes Twitch chat!

Exciting clip of the last minute of the duel -- spoiler alert: https://www.twitch.tv/nealwu/clip/ConfidentGenerousTarsierDoubleRainbow

CF Hot News: Seattle Builds galen_colin orz Statue

Good morning everyone!

We have just received word that the City of Seattle has completed their recently funded galen_colin orz statue. City planners say that this is the latest update in their recent endeavor to honor their favorite CF personalities.

"I'm proud to announce that the galen_colin orz statue has finally reached completion," announced city planner Vasya. "You know, after we decided to shape the space needle as a symbol praising the great Monogon, some of us thought that we would never be able to make such an amazing work of art again. We're truly delighted that we were able to prove all the skeptics wrong with this new piece."

The project was built entirely using renewable energy created by water turbines run exclusively on the tears of java programmers TLEing on system tests. The city hopes that, with enough publicity, the statue might one day become a tourist attraction.

Is the "Update Contest" button for gym contests suppose to work while the contest is going on? I would like to fix a small issue with one of the statements in the ongoing Treap set, and add a testcase to another problem to make a certain solution to TLE. I have updated both statements on polygon, and rebuilt the packages.

When I try to click the "Update Contest" buttons to move these into the live gym set, CF redirects me to the "All your bugs are belong to us" page. Do any problem authors know if this is a known bug, and if so, is there a workaround? It seems like it has been broken for about 10 hours now, so it doesn't look like a transient issue.

Algorithms Thread Episode 9: Treaps

Good morning everyone!

Episode 9 of AlgorithmsThread comes out shortly after the Div2 round ends. This episode is on Treaps! It covers:

• Fundamentals of Treaps
• Splitting and Merging
• Range reversing

... and more! I also decided to keep up the super-high quality style and made a custom gym set with 5(+2) original problems to make sure you really understand everything that was covered in the lecture. The gym set will be released shortly after the lecture ends, and I hope that the problems will be challenging and fun, even for people who aren't seeing treaps for the first time.

If you have any questions or suggestions, feel free to leave them below. I hope you enjoy the problem statements, and, in the spirit of the upcoming holiday, I'll leave you all with this:

Update: The scoring distribution for this round will be: 1 — 1 — 1 — 1 — (+1) — (+1) — 1

Update2: Solution video is out now and solutions to all problems are available here. Hope you all enjoyed the contest!