Hi all,

The final contest of the 2019-2020 USACO season will be running from March 27th to March 30th. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

The 2020 ICPC North America Championship 2020 is today!

The 60 best teams from North America will compete for the title of North America Champions, a trophy and also an opportunity to represent North America at the ICPC World Finals 2020 in Moscow, Russia! Join us for a live broadcast or just follow the contest through all the possible links below.

Today's live broadcasters will be ecnerwala, scott_wu, tehqin, and xiaowuc1. Live commentary will start at 10 AM EST!

Official Website: https://nac.icpc.global/

Hashtag: #icpcnac2020

Discord: https://discord.gg/FpJfBHS

Mirror contest: https://open.kattis.com/contests/nac20open

Scoreboard: http://nac.icpc.global/scoreboard/

Live broadcast: https://www.youtube.com/channel/UC6-6qLP8Fubg5F3r4tfbosw and https://www.twitch.tv/icpclive

Twitter: https://twitter.com/IcpcNac

Facebook: https://www.facebook.com/na.icpc.io

Flickr: https://www.flickr.com/photos/187051365@N06/

Hi all,

The third contest of the 2019-2020 USACO season will be running from February 21st to February 24th. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Some of the North American ICPC teams were upsolving NWERC 2011 and on problem G ran into issues where Bellman-Ford would not properly detect the presence of a negative weight cycle. Here's an example of a submission that uses Floyd-Warshall with no epsilons and gets AC, and here's an example of a submission that uses Bellman-Ford with no epsilons and gets WA. I believe that Bellman-Ford gets AC with no epsilon if you use long double.

The problem statement has this claim that an error of magnitude less than 1e-7 in one distance computation will not affect the answer. What is the proper way to interpret this claim in the context of implementing a solution to this problem? Furthermore, is the Bellman-Ford algorithm actually not robust in this manner, whereas Floyd-Warshall is robust?

Hi all,

The second contest of the 2019-2020 USACO season will be running from January 17th to January 20th. 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.

Edit 2: Due to a configuration error, the contest is running for 12 more hours than originally stated. The contest window is still open, please wait for the window to expire at 4:00 AM UTC on January 22nd before discussing.

Edit 3: Results can be found here.

https://zibada.guru/finals/ is a good resource up to 2008, but do such detailed scoreboards exist pre-2008? The ones that the ICPC website releases leave much to be desired in terms of which problems were solved, when, and by which teams...

Hi all,

The first contest of the 2019-2020 USACO season will be running from December 13th to December 16th 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.

Edit 2: Even though it is impossible to start the contest after 23:59 UTC-12, contestants who start right at that point in time still get a full four hours to do the contest. Therefore, please do not discuss the contest until 4:00 UTC-12 on December 17.

Edit 3: Results can be found here.

Hi all,

The final contest of the 2018-2019 USACO season, the US Open, will be running from March 29th to April 1st! Good luck to everyone! As a courtesy to your fellow contestants, please wait until the contest is over for everyone before discussing problems here.

Edit 1: The contest is live! Please do not post any spoilers about the problems publicly — if you have any issues with the problem statements, please follow the instructions to voice your concerns.

Hi all,

The third contest of the 2018-2019 USACO season will be running from February 22nd through February 25th, and will be the final regular contest before the US Open. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Edit 1: The contest will open soon! If you see any issues with any of the problems, please follow the instructions here letting the contest director know what issues you have. Please do not complain about them on this blog post — that may spoil the problems for other contestants and it will not result in your issues being resolved. Good luck to all contestants!

Edit 2: The contest will end in under 24 hours! As a reminder, since all contestants get a full four hour contest window irrespective of when they start, please hold off discussion of the contest until everyone has finished the contest (4 AM UTC-12).

Hi all,

The second contest of the 2018-2019 USACO season will be running from January 18th to January 21st. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

EDIT: As a reminder, do not post any spoilers until the contest is over, which will be at 4 AM UTC-12 on January 22nd. If you have any issues with the problem statements, please consult the rules on how to contact the contest administrators. The administrators do not monitor social media.

Hi all,

The first contest of the 2018-2019 USACO season will be running from December 14th to December 17th. Good luck to everyone! Please wait until the contest is over for everyone before discussing problems here.

Some friends have reported that https://www.lydsy.com/JudgeOnline/registerpage.php is no longer working. Is this intentional?

A lot of, if not all, of the SGU problems come from old contests, though the SGU problem statements themselves often do not have the contest attribution associated with them. For example, problems 542 through 553 are the 2012 NEERC Southern Subregional, but that attribution is not present in the problem statements (as of the time of this post). Compare this with problems 201 through 208, which are stated as being part of a Petrozavodsk training contest (specifically ASC 2, though that is not explicitly mentioned in the statements).

I'd like to assemble/crowdsource a comprehensive mapping of SGU problem IDs to the contests where the problems were originally hosted, and additionally links to them in the Codeforces gyms if they're hosted there. Does anyone have this mapping? I'm curious if the admins or anyone familiar with how the SGU problems were sourced to begin with can help out here, otherwise this can be easily crowdsourced.

• 193-200: http://codeforces.me/gym/100199 (ASC 1)
• 201-208: http://codeforces.me/gym/100197 (ASC 2)
• 209-217: http://codeforces.me/gym/100198 (ASC 3)
• 296-305: http://codeforces.me/gym/100765 (NEERC Southern Subregional 2006)
• 306-314: http://codeforces.me/gym/101365 (Petr Mitrichev Contest 1)
• 326-335: http://codeforces.me/gym/101366 (Petr Mitrichev Contest 2)
• 346-357: http://codeforces.me/gym/101503 (NEERC Southern Subregional 2007)
• 368-379: http://codeforces.me/gym/101591 (Saratov SU Contest, Summer Petrozavodsk 2008)
• 392-402: http://codeforces.me/gym/101504 (NEERC Southern Subregional 2008)
• 414-422: http://codeforces.me/gym/101367 (Petr Mitrichev Contest 3)
• 423-432: http://codeforces.me/gym/101368 (Petr Mitrichev Contest 4)
• 443-452: http://codeforces.me/gym/100837 (Japanese Contest 3, Summer Petrozavodsk 2009)
• 453-463: http://codeforces.me/gym/101252 (NEERC Southern Subregional 2009)
• 464-473: http://codeforces.me/gym/100206 (Goryinyich Challenge X)
• 474-484: http://codeforces.me/gym/100761 (Halloween Contest 2009, problems A-K only)
• 485-496: http://codeforces.me/gym/101411 (NEERC Western Subregional 2009)
• 497-507: http://codeforces.me/gym/101370 (Petr Mitrichev Contest 5)
• 508-517: http://codeforces.me/gym/101371 (Petr Mitrichev Contest 6)
• 518-529: http://codeforces.me/gym/101246 (NEERC Southern Subregional 2010)
• 530-541: http://codeforces.me/gym/100151 (NEERC Southern Subregional 2011)
• 542-553: http://codeforces.me/gym/100109 (NEERC Southern Subregional 2012)

Hi all,

Inspired by stevenkplus and scott_wu, I will be hosting a livestream on Sunday, June 3rd, at 10 AM PDT of my virtual participation in Codeforces Round 486. I'll be streaming at https://www.twitch.tv/xiaowuc1 for approximately two hours. Hope to see you there!

Edit 1: This stream is going live in under an hour! I'll try to start it a few minutes before 10 AM to make sure that audio and video are working properly, with the actual solving starting no earlier than 10 AM.

Hi all,

The US Open and final contest of the 2017-2018 USACO season will be running from Friday, March 23rd to Monday, March 26th.

As always, please wait until the contest is over for all competitors before discussing any specifics of the contest here.

Update: The contest is now live! Good luck to all competing!

Hi all,

The third contest of the 2017-2018 USACO season will be running from Friday, February 23rd to Monday, February 26th. This will be the last contest before the US Open, scheduled for March 23rd to March 26th.

Please wait until the contest is over for everyone before discussing problems here.

Hi all,

The second contest of the 2017-2018 USACO season will be running from Friday, January 19th to Monday, January 22nd.

Please wait until the contest is over for everyone before discussing problems here.

Update: The contest is now live!

Hi all,

The first contest of the 2017-2018 USACO season will be running from December 15th to December 18th. Good luck to everyone as we start our season! Please wait until the contest is over for everyone before discussing problems here.

Update 1: The contest is now live!

Hi all,

The third contest of the 2016-2017 USACO season will be open from February 10th to February 13th. This will be our last contest before the US Open. Feel free to discuss the problems here after the contest is over!