This weekend, we will host the 2nd Universal Cup Semifinal. Unlike with previous Universal Cup rounds, there will be exactly one window that all teams will participate in. This window will be from 5pm to 10pm UTC+8 on Sunday, June 23rd. Note that this window is after the onsite version.

Any Universal Cup registered team can participate. If you are new here, please register following the instructions on Registration.

Besides competing to advance to the Universal Cup Finals, sponsored by Huawei, we have also prepared prizes for teams in the top 10 (excluding onsite teams in the Summer Summit) . The prize details are as follows (may be replaced by products of similar value):

After the online semifinal, we will host a stream of all onsite teams competing in the Semifinal at the Summer Summit event in Cancun, along with problem analysis. The stream will start immediately after the end of the online version at 10pm (UTC +8) and end at 3am (UTC +8). We will run livestreams in English and in Chinese as follows:

• English: YouTube through tourist's account!

• Chinese: Bilibili through jiangly's account!

Who are you cheering on to win the onsite Semifinals? Here are the teams:

We look forward to your participation!

The trial round of the third Universal Cup is happening the weekend of June 1st. The contest is based on the North America Championship, which took place in Florida on May 27th, 2024. The top 50 teams in North America competed for qualification to World Finals.

There are eight time windows for you to join:

• June 1st 08:00 — 13:00 (UTC +8)
• June 1st 10:00 — 15:00 (UTC +8)
• June 1st 13:00 — 18:00 (UTC +8)
• June 1st 16:00 — 21:00 (UTC +8)
• June 1st 19:00 — 00:00 (UTC +8)
• June 1st 21:00 — 02:00 (UTC +8)
• June 1st 23:00 — 04:00 (UTC +8)
• June 2nd 02:00 — 07:00 (UTC +8)

Because this is the trial round, it will be unrated.

We look forward to your participation!

Hi all,

The final contest of the 2023-2024 USACO season will run from March 15th to March 18th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on March 15th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Can I use AI tools during the contest including but not limited to ChatGPT and Copilot?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Probably not. Petition IOI to add Rust support first.

Hi all,

The third contest of the 2023-2024 USACO season will run from February 16th to February 19th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

Note: The USACO website has been switched over to HTTPS and some other upgrades have happened since the last contest.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on February 16th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Can I use AI tools during the contest including but not limited to ChatGPT and Copilot?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Probably not. Petition IOI to add Rust support first.

NOTE: The USACO website has been targeted by a DDoS attack and may be down for the duration of the contest.

Hi all,

The second contest of the 2023-2024 USACO season will run from January 26th to January 29th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on January 26th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Can I use AI tools during the contest including but not limited to ChatGPT and Copilot?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Probably not. Petition IOI to add Rust support first.

Hi all,

The first contest of the 2023-2024 USACO season ran from December 15th to December 18th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

There are some new rules regarding the platinum division of USACO, please refer to the website regarding the updates, especially if you are trying to be invited to the USACO training camp.

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on December 15th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Can I use AI tools during the contest including but not limited to ChatGPT and Copilot?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Why didn't I get an email from USACO when I registered my account?

Follow the directions on the USACO website regarding Gmail Delivery Issues to contact the contest director.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Probably not. Petition IOI to add Rust support first.

I was motivated to write this blog post after reading this blog post about possible precision issues in output and requiring printing a rounded answer exactly instead of printing an answer within a tolerance. This blog post feels somewhat related insofar as that it has an issue with floating point numbers, and also a doubt as to the correctness of the underlying data. Alternatively, someone can find the mistake in my logic.

The problem in question is Rationalization which asks to find a positive rational $$$\frac{A}{B}$$$ that is within a range $$$[C-F, C+F]$$$. Among all such fractions, minimize $$$A$$$, and among all such with minimal $$$A$$$, minimize $$$B$$$. The judge data guarantee that $$$1 \le A, B < 10^6$$$.

My solution path is as follows: If $$$C-F \le \frac{A}{B} \le C+F$$$, then $$$B(C-F) \le A \le B(C+F)$$$. Therefore, we can just check all $$$B$$$ in increasing order and find the smallest $$$B$$$ where $$$[B(C-F), B(C+F)]$$$ contains some integer, and the smallest such integer should be our $$$A$$$.

Now, $$$C$$$ and $$$F$$$ are floating-point numbers, so in order to make sure that we can represent $$$C-F$$$ and $$$C+F$$$ exactly, we scale them up by powers of 10 until they are exactly integers. Fortunately, we're guaranteed that these numbers are written in decimal form.

c, f = input().split()
if '.' not in c:
  c += ".0"
if '.' not in f:
  f += ".0"
if c[2] != '.':
  c = "0" + c
if f[2] != '.':
  f = "0" + f
while len(c) != len(f):
  if len(c) < len(f):
    c += "0"
  else:
    f += "0"
scale = 10 ** (len(c)-3)
c = int(c[0:2] + c[3:])
f = int(f[0:2] + f[3:])
num = scale
MAXVAL = 10 ** 6
for b in range(1, MAXVAL):
  while num < b * (c-f):
    num += scale
  if num <= b * (c+f):
    assert (num // scale) < MAXVAL
    print(num // scale)
    print(b)
    found = True
    break
assert found

This gets 60 points on Kattis with a WA verdict on the final subtask, so it does print something which is deemed incorrect (as opposed to printing nothing or printing a value of $$$A$$$ that is too large and getting RTE). Since the solution does pass the first two subtasks, I am reasonably confident that it is not completely wrong. I presume that the second subtask is meant to admit solutions that have precision issues by representing values using floating point values (perhaps by scaling each of the floating point values directly by $$$B$$$), though I haven't bothered to experiment much there.

I do have a weak prior that some Kattis problems with floating point numbers do something incorrect — for example, for this problem, all reference solutions say that three points are collinear if and only if the turn would be at most $$$10^{-9}$$$ degrees, as opposed to checking collinearity exactly.

Because of this prior, I'd like to identify the test case to see where I went wrong. Sadly, I can't find the input data for this problem, so I'm stuck trying to find a bug in my solution/logic or conclude the test data are wrong. I'd just like to ask the author for test case 77 to verify it by hand. In the interim, I might be able to get the test case in a few hours if I can find a way to AC the first 76 cases and differentiate that I'm in test case 77. (Kattis only allows 10 submissions within a 10 minute window.)

Alternatively, did I go wrong somewhere?

Update 1: Test case 77 has c = 7.80212 and f = 0.0000000684. I wrote a slow program that seems to generate the same output as what my program prints.

from fractions import Fraction
c = Fraction('7.80212')
f = Fraction('0.0000000684')
lhs = c - f
rhs = c + f
for a in range(8, 10 ** 6):
  found = False
  b = max(1, int(a / rhs))
  while b < 10 ** 6:
    cand = Fraction(a, b)
    if cand >= lhs and cand <= rhs:
      print(a)
      print(b)
      found = True
      break
    if cand < lhs:
      break
    b += 1
  if found:
    break

This fraction is not equal to either of $$$C-F$$$ and $$$C+F$$$.

Update 2: jeroenodb was able to AC the problem and with his solution we were able to prove that the test data are indeed incorrect. I have contacted Kattis to try to get this rectified.

The 19th round of the first Universal Cup is happening the weekend of June 3rd. The contest is based on the North America Championship, which will take place in Florida on May 29th, 2023. The top 51 teams in North America will be competing for qualification to World Finals.

As always, there are three time windows for you to join:

• June 3rd 13:00 — 18:00 (UTC +8)
• June 3rd 19:00 — 24:00 (UTC +8)
• June 4th 02:00 — 07:00 (UTC +8)

Please note that you can see two scoreboards in DOMjudge. The 'Local Scoreboard' shows the standings ONLY IN THE CURRENT TIME WINDOW. And the 'Combined Scoreboard' shows all participants, including the onsite participants, and the cup participants in the previous time windows.

Special note: The North America Championship intends on running an open contest in parallel to the contest. Teams that compete in the open contest can request to have their results merged into the combined scoreboard. Teams that intend on competing in the Universal Cup stage should not look at the problems or attempt to solve them in the mirror.

Contest link: https://domjudge.qoj.ac/

Universal Cup Scoreboard: https://qoj.ac/ucup/scoreboard

About Universal Cup:

Universal Cup is a non-profit organization dedicated to providing trainings for competitive programming teams. Up to now, there are more than 600 teams from all over the world registering for Universal Cup.

A more detailed introduction: https://mirror.codeforces.com/blog/entry/111672

Register a new team: https://ucup.ac/register (the registration request will be processed before each stage)

Results of the past stages: https://ucup.ac/results

Terms: https://ucup.ac/terms

Ratings: https://ucup.ac/rating

Hi all,

The final contest of the 2022-2023 USACO season will be running from March 24th to March 27th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on March 24th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Why didn't I get an email from USACO when I registered my account?

Follow the directions on the USACO website regarding Gmail Delivery Issues to contact the contest director.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Petition IOI to add Rust support first.

Hi everyone! I have been inspired by recent events to write this blog post. This list is not comprehensive, but mostly because I do not keep detailed logs of problems I have written.

There are a few things you will notice after reading through these problems. In no particular order:

1. Most of these problems are not "high-quality" — they would never see the light of day on a CF round for example. This is mostly due to my lack of skill in generating "high-quality" problems. You'll see that a lot of my problems are generated from observing real-life events and then constructing problems out of those scenarios. There are many ideas that have been proposed and thrown into the void because they were worse. I think there are a couple problems in this list that are actually good problems, but most of them I am not particularly proud of.
2. The difficulties on these problems generally lean easy, and the problems almost always lean standard. My problemsetting ideology for contests is to set the easiest possible problem to get the desired results. This frequently results in problems where the idea is very straightforward, but maybe obfuscated in a minor way. This is also because most of my problem setting is for my local regional contest, where there are two divisions and because people love to propose hard problems, I get to fill in the gap with easy problems.
3. I like to embed random references into my problems. They don't mean anything in particular, but, for example, people who are friends with me on Facebook know that I upload quarterly photo albums and the album name is usually a song that I enjoyed listening to that quarter. I'm a nostalgic person.
4. It turns out a bunch of the problems I wrote have appeared in very similar forms before. Any such problems I am aware of are labeled as such. Please include more examples in the comments.
5. I'm probably not done authoring problems. I expect a lot of criticism in the comments.

When preparing the problems for the February 25th NA ICPC regionals, we had some discussion around how lists should be formatted when given as input to contestants.

The primary argument motivating some design decisions was consistency — namely that all lists should be formatted the same way, where a list should be expressed by starting with the length of the list, $$$n$$$, and then writing $$$n$$$ lines, one item per line.

This is pretty standard and for most problems, this is the convention that most problems use for most lists. The main counterexample to this case seems to be when the list is a list of integers. A lot of problems, when confronted with a list of $$$n$$$ integers, will write out the list as one line of $$$n$$$ space-separated integers. This seems to be the meta for most contests, though I have not looked very carefully at this so this assumption may be wrong. NA ICPC is one of the contests that generally follows line-delimited lists of integers.

Here's my question to the competitive programming community at large — as a contestant, how do you feel about input formatting of this form?

• Consistency is the most important thing, so all lists should be written as $$$n$$$ followed by $$$n$$$ lines, one per object.
• Consistency is not that important. For complicated lists where the object is not just a single string or an integer, I prefer lists to be written as $$$n$$$ followed by $$$n$$$ lines, one per object. However, for lists of integers or strings, I prefer $$$n$$$ on one line followed by another line with $$$n$$$ space-separated tokens.
• Consistency is not that important, and I don't care how lists of $$$n$$$ integers are written, since I'll just read them the same way no matter what.
• I don't believe that lists by default should be written as $$$n$$$ followed by $$$n$$$ lines, one per object.

I also want to ask a similarly related question — as a contestant, have you thought about consistency of input formats in programming contests?

• Yes, and it bothers me when contests are internally inconsistent with regards to reading until EOF or a sentinel, or having a prespecified $$$n$$$.
• Yes, and it bothers me when different contests follow different formats.
• Yes, but I don't really care.
• No.

Hi all,

The third contest of the 2022-2023 USACO season will be running from February 24th to February 27th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on February 24th.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Why didn't I get an email from USACO when I registered my account?

Follow the directions on the USACO website regarding Gmail Delivery Issues to contact the contest director.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Petition IOI to add Rust support first.

Hi all,

The second contest of the 2022-2023 USACO season will be running from January 27th to January 30th. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

The contest will open on January 27th. A link to the contest will be posted here shortly after the contest opens.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Why didn't I get an email from USACO when I registered my account?

Follow the directions on the USACO website regarding Gmail Delivery Issues to contact the contest director.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Petition IOI to add Rust support first.

Hi all,

The first contest of the 2022-2023 USACO season will be running from December 16th to December 19th this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

For those unfamiliar with the USACO contest format, please refer to the contest instructions and rules. We provide a short FAQ but folks should read all the rules carefully.

I have a question about the contest. Where do I ask it?

Email the contest director via the instructions above. Do not post anything publicly about the questions (including but not limited to your scores, how you felt about the problems, any content of the problems, etc) until after the contest is over for everyone. Do not DM me or anyone else affiliated with USACO, only the contest director can assist you. The contest director does not monitor Codeforces, this blog post is merely a courtesy to inform other people of the contest.

When can I enter the contest?

This contest runs until December 19th, 23:59 UTC-12 and is four hours long. The URL for the contest page can be found here.

If I submit multiple programs, which one gets evaluated?

Only the last submission will be evaluated for official scoring purposes.

Can I use prewritten code / templates?

No.

Am I allowed to use outside resources during the contest?

You may only refer to language documentation.

Why didn't I get an email from USACO when I registered my account?

Follow the directions on the USACO website regarding Gmail Delivery Issues to contact the contest director.

Can I solve problems in Rust?

No, the only languages supported are C, C++, Java, and Python. Consult the instructions for language-specific technical details.

Will Rust support be added?

Probably not. Petition IOI to add Rust support first.

Hi all,

The final contest of the 2021-2022 USACO season will be running this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

Is there a released PDF of the problem statements? The published link on the website 404's, it is possible to download the full Polygon package and get TeX statements that way but it does seem bad to have links on the website that are 404'ing.

(Incidentally, will this contest get uploaded to the CF gym? I recall old Northern subregionals being uploaded but don't seem to see this one either.)

Hi all,

The third contest of the 2021-2022 USACO season will be running from February 25th to February 28th this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

Hi all,

The second contest of the 2021-2022 USACO season will be running from January 28th to January 31st this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing anything contest-related (including but not limited to your scores or anything about the problems).

Hi all,

The first contest of the 2021-2022 USACO season will be running from December 17th to December 20th this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Edit 1: The contest is live now! Please read the contest rules carefully, especially regarding how to ask clarifications or contact the contest organizers. Do not spoil anything (including but not limited to your scores or anything about the problems) about the contest until the end of the contest (four hours after the stated deadline of the contest).

Edit 2: Results have been released.

On szkopul, I'm seeing problem statements where the \n character appears instead of actual newlines, even in sample input/output. Other non-ASCII characters appear to be written in escaped format also instead of rendered properly.

I'm curious if this is a local issue for just myself and, if not, if anyone has a good short-term fix for this.

Problem statement

This problem looks like a fairly standard tree DP problem, I won't spoil the solution in case people want to think about it.

However, the reason why this problem is interesting (or perhaps extremely painful) is that the memory limit is 32MB. Given that $$$N$$$ can be 1.5 million, this means you're not even allowed to store $$$6N$$$ 32-bit integers.

Therefore, it seems that the main challenge of this problem is to be able to fit everything inside such a tight memory limit. Notably, I've gotten MLE just trying to read in the input and trying to get the tree stored in a representation that makes it possible for me to start working on the DP part of the problem.

In the modern era, memory limits are no longer this tight, but a lot of problems on szkopul retain these tight memory limits which occasionally makes it an interesting (or perhaps extremely painful) challenge to figure out how to fit things in the memory limit.

What's intended here? I asked about this problem in the AC server and got some advice with things such as relabeling the tree with ETT or simulating DFS without an explicit stack. It feels like the authors intended for some precise $$$5N + \mathcal{O}(1)$$$ memory solution and it's a little alarming that I can't even get beyond "read the input and come up with some representation for the tree" without getting MLE.

Hi all,

The final contest of the 2020-2021 USACO season will be running this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Hi all,

The third contest of the 2020-2021 USACO season will be running from February 26th to March 1st this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Hi all,

The second contest of the 2020-2021 USACO season will be running from January 22nd to January 25th this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Edit 1: The contest is now live! Please do not spoil anything about the contest publicly until the contest is over for everyone, and please report any issues with the contest directly to the contest administrator via the instructions instead of posting them here.

Hi all,

The first contest of the 2020-2021 USACO season will be running from December 18th to December 21st this weekend. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Edit 1: The contest is now live! There are new changes to how USACO contests are run — the most notable change is that I/O is no longer done via files. Please consult the official rules for all the changes.

Edit 2: Although the contest window is almost over, please do not discuss the contest until everyone has finished it. The contest window should close four hours after it officially ends since folks who join at the last minute purportedly still get a full window, in which case the contest ends at this time.

Edit 3: The contest is officially over — hope everyone enjoyed the contest! Results should hopefully be ready by the end of the week.

Edit 4: Results are out!