There was recently an update to the rules for the ICPC World Finals.

I think the change most contestants would care about is the change of medal distribution, which used to be 4-4-4 but has now been updated to 4-6-10.

We have finalized the teams that will be competing in the 3rd Universal Cup finals! They are as follows:

We will be running a livestream and a mirror contest on contest day, stay tuned for more details! To see the full schedule, check out the announcement blog.

Hello Codeforces! We are glad to invite you to follow the 2026 ICPC North America Championship!

The live broadcast will be on the ICPC Live YouTube channel starting at 10am EDT!

Some other links for more NAC content!

• Photo gallery
• NAC Scoreboard
• NAC Problemset
• NAC Online Judge — register here!
• NAC Facebook

If you have any fun facts about NAC teams, please submit them here!

Good luck to all teams!

The third contest of the 2025-2026 USACO season will run from February 20th to February 23rd. 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 US high school students vying for IOI, there are some new rules regarding the format this year, please refer to the website regarding the updates.

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?

For bronze and silver, the contest will open on February 20th. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

The second contest of the 2025-2026 USACO season will run from January 30th to February 2nd. 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 US high school students vying for IOI, there are some new rules regarding the format this year, please refer to the website regarding the updates.

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?

For bronze and silver, the contest will open on January 30th. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

The first contest of the 2025-2026 USACO season will run from January 9th to January 12th. 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 US high school students vying for IOI, there are some new rules regarding the format this year, please refer to the website regarding the updates.

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?

For bronze and silver, the contest will open on January 9th. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

Hello, Codeforces!

As most of you know by now, the ICPC World Finals are happening in Baku! Many of the staff members are ICPC alumni and we want to meet as many of you in attendance as possible!

For those who are less interested in Tetris or push-ups and more interested in discussion around programming contests, please find me at 20:30 on Tuesday, September 2nd to talk about Universal Cup!

What is Universal Cup? We're an organization that runs contests throughout the year for the competitive programming community. We recently ended our third season with the 3rd Universal Cup Semifinals and are hoping to start Season 4 soon!

Qingyu, cofounder and co-president of Universal Cup, as well as cubercsl, core member of the Universal Cup Technical Committee, will be joining me! I hear people who visit us might get some small gifts...

The complete alumni schedule can be found at https://worldfinals.icpc.global/alumni.html.

The final contest of the 2024-2025 USACO season will run from March 21st to March 24th. 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 gold division of USACO, please refer to the website regarding the updates, especially if you are trying to promote into platinum.

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?

For bronze and silver, the contest will open on March 21st. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

The third contest of the 2024-2025 USACO season will run from February 21st to February 24th. 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 gold division of USACO, please refer to the website regarding the updates, especially if you are trying to promote into platinum.

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?

For bronze and silver, the contest will open on February 21st. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

The second contest of the 2024-2025 USACO season will run from January 24th to January 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).

There are some new rules regarding the gold division of USACO, please refer to the website regarding the updates, especially if you are trying to promote into platinum.

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?

For bronze and silver, the contest will open on January 24th. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

The first contest of the 2024-2025 USACO season will run from December 13th to December 16th. 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 gold division of USACO, please refer to the website regarding the updates, especially if you are trying to promote into platinum.

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?

For bronze and silver, the contest will open on December 13th. For gold and platinum, the contest opens at 12pm ET on Saturday, and you must start the contest between 12pm and 12:15pm ET on Saturday to get a certified score.

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.

We have finalized the 20 teams that will be competing in the 2nd Universal Cup finals! They are as follows:

We will be running a livestream and a mirror contest on contest day, stay tuned for more details! To see the full schedule, check out the announcement blog.

While we eagerly await the official announcement of which teams are competing in the 2025 ICPC North America Championship, there is some demand within NA to see who is competing! Please comment with your CF handles if your team will be attending!

Note: As of the time of this post, not all divisional wildcards have been included (waiting for explicit confirmation from teams), nor global wildcards.

East Central North America

Greater New York

Mid-Atlantic USA

Mid-Central USA

North Central North America

Northeast North America

Pacific Northwest

Rocky Mountain

South Central USA

Southeast USA

Southern California

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 $$$1 \le A, B \lt 10^6$$$.

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://codeforces.me/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.