I'm sadly announcing that a2oj.com (A2 Online Judge) will be retiring by end of 2019, I'll shut it down at midnight on New Year's Eve. It was something I took care of for about 10 years.

I'm really sorry, but I prefer not to explain my reasons, so please don't ask me why I'm doing this, it was hard enough for me to make this decision, and also please don't try to convince me to change my mind.

I'd like to say thank you to everyone who used it, and please accept my sincere apologies for shutting it down.

If you have something good to say about A2OJ (how you used it or how it helped you in any way), I'd love to read that, please send it to the following email (or in a comment here): bye@a2oj.com

Also please feel free to take a copy of any data you can access, and if you need some data in a specific format, please send your request to the following email: bye@a2oj.com (if the data isn't public, make sure to send from your registered and verified email which can access this data). I'll do my best to fulfill all requests.

Please only use the above email, because soon I'll be deactivating my personal Facebook account again, I'll also deactivate A2 Online Judge.

Edit 1: I'll keep a static version of all Ladders & Categories.

Edit 2: Here's how I generated the ladders, in case if anyone wants to implement it: https://mirror.codeforces.com/blog/entry/47442

Edit 3: A2 Online Judge is shut down now, and a static version of all ladders and categories is available. And here are some final numbers for the record:

Database numbers:

• 24,012,628 total number of database rows.
• 99,242 registered users.
• 33,133 created contests.
• 1,581,430 submissions collected from other online judges.
• 937,658 different source codes stored in the database.
• 261,733 compiled and executed source codes (in 54 different languages).
• 6,144,545 user solved problem entries (detected that a user solved a problem).
• 377,580 problems added to contests.

Google Analytics numbers:

• 30,265,387 page views.
• 5,252,045 sessions.
• 1,157,668 users.

Top 10 countries from Google Analytics:

1. India
2. Egypt
3. Brazil
4. United States
5. Bangladesh
6. Peru
7. Jordan
8. Syria
9. Colombia
10. Bolivia

ltaravilse, he was that kind, funny and super helpful guy. I'm sure many of us interacted with him some how, and I was lucky to meet him in person more than once. Everyone from the old TopCoder days should remember him.

Sadly, and I still can't believe it, he passed away yesterday. This is a really sad event for the whole competitive programming community. People from South America can tell more about how kind and helpful he was.

MikeMirzayanov, can we please have a round in his name?

Rest in peace my dear Leo.

Over a year ago I created some ladders on A2OJ, you can read the details of these ladders here.

Some people asked me to create more similar ladders, so for each rating range I created another ladder using a similar criteria which I used for the old ladders, with 200 problems in each ladder and none of them exists in any of the old ladders (they are bit harder than the old ladders).

Also I added another feature, now you don't need to go and click on the link in A2OJ to update your solved problems, all what you need to do is to include your Codeforces handle in your account page, join the ladder and start solving, once you solve a problem, A2OJ will detect that within a minute or so.

I have a small request if you are reading this and practiced using the old ladders, please let me know in a comment if these ladders really helped you, also please let me know if you have any suggestions, and thanks a lot in advance.

i need 4 original problems similar to div2 a, b, c & d. i'm willing to pay in dollars if i use your problems. if you can get some original problems 100% ready within 24 hours, please send me a private message.

edit: i already got a lot of responses, thanks everyone

I always wanted to make something like a guide for anyone who wants to be better at competitive programming. But I believe that I'm not experienced enough to make this guide.

So, here is what I did and I hope it will be helpful to many of you:

• Out of more than 80,000 rated Codeforces users, I selected just 700 of them who satisfied the following conditions:

1. Over the period of 1-2 years, their rating increased step by step more than 600 points in total (their graph looks linear in a period of 1-2 years with increment of more than 600 points).
2. They participated in at least 20 rated contests.
3. They solved at least 150 problems in practice in this period.

• For each rating range, interestingly I found many common problems solved by these users when their rating was in that range. I found the most 100 solved problems in that rating range.

• I created a ladder for each range, and the problems inside it are sorted based on an accurate difficulty level I calculated.

I believe if someone manages to solve (or at least understands the solution from someone else or the editorial) all these problems, they will notice some significant improvements in their skills and rating.

You can find the ladders at the top here: https://a2oj.com/ladders

Also please share this with anyone who might be interested.

P.S. I know that a ML model might do a better job, but the reason why I didn't do this, because I didn't have enough data.

[Edit] I created more ladders, you can read about that and other new feature here.

I can't really describe how happy I'm because of all the support I got from everyone. Huge thanks to everyone!

Yesterday I successfully finished migrating the website to AWS, and it's running now. I know there are some bugs/issues needs to be done, and to do the promised rewards, I'll do that as soon as possible.

Thanks a lot everyone!

Hello everyone,

Several people are asking me when A2 Online Judge is coming back, and unfortunately the issue this time might take longer to fix it.

This is the server which was hosting the website in my garage for several years:

And I think it's time to move to the cloud, but this requires some money. I created a campaign to raise $3000 which I need to host it on AWS for the next 3 years at least. You can read more details here: https://www.gofundme.com/support-a2oj

Please support to bring the website back, even if by just sharing the campaign.

Thanks in advance,

Ahmed Aly

I'm working on a chat bot that will look like this (watch the video): https://goo.gl/OsSdb3

I still have a lot of work to do, and I'll wait for Facebook approval to make this available to everyone which might take weeks.

I have countless number of ideas, it can be something like your virtual coach who suggests problems to solve or editorials/algorithms to read, which remembers your history and suggests something suitable for you.

In the above page you can subscribe to get an email when this is live to everyone, but what I need the most right now, is ideas. Please if you have any idea, you can write it in the above link or just write it in a comment here. Thanks in advance.

After running the contest in the past 4 years, I'm back to participate as a contestant again in Google Code Jam. And since I almost didn't solve problems recently, so I wanted to make few warmups for Code Jam.

I will make a short daily warmup contest until Code Jam qualification round, and after the qualification round I'll make it less frequent. Each contest will be 2 hours long, and will contain 5 problems. All problems will be from Codeforces. Until the qualification round, I'll select easy-medium problems, and after that I'll select harder problems, the problems difficulty will be similar to the difficulty of the coming Code Jam round.

I'll start with 4 contests starting from tomorrow, one every day and they will start at the same time.

Here are the first 4 contests:

• http://a2oj.com/contest?ID=24957

• http://a2oj.com/contest?ID=24958

• http://a2oj.com/contest?ID=24959

• http://a2oj.com/contest?ID=24960

Edit 1: The first contest is over, with 35 contestants who made at least 1 submission, and 200 submissions in total. It was a good warmup for me.

ِEdit 2: The second contest will start in 30 minutes. http://a2oj.com/contest?ID=24958

ِEdit 3: The third contest will start in 30 minutes. http://a2oj.com/contest?ID=24959

Unfortunately, for technical reasons, my scoreboard will not work.

Recently I added a new feature in A2 Online Judge, it's called Practice Ladders. A practice ladder is just a list of problems, and you can add some dependencies between the problem (for example, you must solve problem X before being able to see problem Y). Also you can add dependencies between the ladders and each other (for example, you must solve all problems in ladder X before being able to see any problem in ladder Y).

Also I created 7 Codeforces practice ladders which should you to increase your level, each ladder contains 100 Codeforces problems. Find which ladder is appropriate for you and enjoy!

Div. 2 A Problems: http://a2oj.com/Ladder.jsp?ID=4

Div. 2 B Problems: http://a2oj.com/Ladder.jsp?ID=5

Div. 2 C Problems: http://a2oj.com/Ladder.jsp?ID=6

Div. 2 D Problems: http://a2oj.com/Ladder.jsp?ID=7

Div. 2 E Problems: http://a2oj.com/Ladder.jsp?ID=8

Div. 1 D Problems: http://a2oj.com/Ladder.jsp?ID=9

Div. 1 E Problems: http://a2oj.com/Ladder.jsp?ID=10

I'm planning to make a scoreboard for the ACM ICPC World Finals 2015, the scoreboard will contain the TopCoder and Codeforces handles for the contestants. It will be similar to this one (but with some more improvements).

Please post the Codeforces handles for the qualified teams here. I'll keep updating this post once I get any new information.

Any suggestions for the scoreboard are welcome for sure.

I'll add all the handles I get in the following table:

Edit: Looks like the following outputs are correct, you can use them to judge your solutions (or you can submit your solutions here). Also it looks like many contestants will fail in the last problem, so I guess the cutoff will be 60 points (anyone with at least 60 points will be qualified).

Until Facebook finishes the manual judging, let's compare our solutions against each other. Here are what I think should be the correct outputs for the given inputs, please run your solutions against these inputs and write a comment here and say what your solution agrees with and what it doesn't.

A. Homework

Full input link: https://drive.google.com/file/d/0ByHbOJKKpXM9dEtiSkxZdExXR00/

Full output link: https://drive.google.com/file/d/0ByHbOJKKpXM9Y1Q0dVZvUkRxanc/

B. Autocomplete

Full input link: https://drive.google.com/file/d/0ByHbOJKKpXM9eklueGpLdmh1ZEE/

Full output link: https://drive.google.com/file/d/0ByHbOJKKpXM9TWdMUVo2amJ2RUk/

C. Winning at Sports

Full input link: https://drive.google.com/file/d/0ByHbOJKKpXM9eTU0YVFRSHUyWTg/

Full output link: https://drive.google.com/file/d/0ByHbOJKKpXM9NnhpX2xfOUlJelU/

D. Corporate Gifting (this is not the output I submitted, what I submitted was wrong)

Full input link: https://drive.google.com/file/d/0ByHbOJKKpXM9elVuOVNld3pRMkE/

Full output link: https://drive.google.com/file/d/0ByHbOJKKpXM9SG43c1R3ZHlrWGc/

The above outputs are not guaranteed to be correct, I'll update the post if I found that any of them is wrong.

Hello everyone,

I'd like to invite you to participate in a contest on A2 Online Judge. The contest problems will be from the ACM Egyptian Collegiate Programming Contest 2014 which was held yesterday.

The problems are not available anywhere yet, so it should be original problem set for anyone who didn't attend the contest. The problems difficulty is medium, and it should be a good team practice if you are preparing for an ACM regional contest.

The contest will follow the ACM standard rules and its duration will be 5 hours (the scoreboard will be frozen during the last hour). It will start this Saturday October 11th at 3pm UTC, check here for the exact time for you.

This is the contest page: http://a2oj.com/Contest.jsp?ID=13748

This is the registration page: http://a2oj.com/Register.jsp?ID=13748

Good luck & Have Fun.

Since TopCoder forums are not that active anymore, and I think Codeforces forums are more active, I decided to start (or continue) the You know your a TopCoder when ... thread here.

It was one of my favorite threads on TopCoder, and I enjoyed reading almost every response.

Let's continue by adding new interesting responses here!

The ACM ICPC 2014 world finals scoreboard will be available here: http://a2oj.com/ICPC.jsp?y=2014

The scoreboard contains many TopCoder and Codeforces handles, and many other useful information, and there is an option to chat with other viewers.

This was last year's scoreboard: http://a2oj.com/ICPC.jsp?y=2013

Special thanks to snarknews for making this list which I'm using. I hope that you will like the scoreboard.

Hello everyone,

Thanks to the new Codeforces API, I'm working on some new Codeforces tools in my website.

If you have any suggestions or you need any tool/feature to exist, please post it here and I'll be happy to implement it if it's possible.

Thanks, Ahmed Aly

A live scoreboard for the ACM ICPC 2013 world finals will be available here: http://ahmed-aly.com/ICPC.jsp

This is just a sample for how it will look like, I might make some small modifications.

The scoreboard displays many information about each team, like the university, the country, the region, the team name, the members TopCoder handles, the members real names and the coach name. Also you will be able to filter the scoreboard by the region or the country. And the scoreboard highlights the champion for each region and shows some icons for the cup and the medals winners.

Edit 1: I added a chatting widget (you can hide it), and the practice contest scoreboard is available now.

Edit 2: Now you can pin your favorite teams to the top of the scoreboard, and you can hide some columns, and there are some statistics rows in the bottom of the scoreboard.

Edit 3: Here is the final ACM ICPC 2013 world finals scoreboard: http://ahmed-aly.com/ICPC.jsp

Hi everyone,

I'm attending the ACM ICPC world finals 2013 in Saint Petersburg, and we are planning to stay for more days after the contest, but we don't have any plans yet. Can you please suggest interesting things/places to do/visit in Russia? Not necessary in Saint Petersburg, we might go to Moscow for example.

Thanks in advance, Ahmed Aly

Hello everyone,

I'd like to invite everyone to participate in a 5-hours Gym contest (both teams and individual participants can join) which will be held this Thursday, January 24th at 04:00 PM MSK (GMT+4), check for other time zones here: http://timeanddate.com/worldclock/fixedtime.html?day=24&month=1&year=2013&hour=16&min=0&sec=0&p1=166 (The registration will be opened 6 hours before the contest)

We will use the problems from the last ACM Arab Collegiate Programming Contest 2012 (English statements only), and the actual contest scoreboard will be merged into the Gym's scoreboard. Please don't participate if you already solved or read the problems. Hopefully the problems will be interesting for both Div1 and Div2 coders.

We encourage you to participate in teams to simulate the actual contest.

I'd like to mention that we used Polygon to prepare the problems for the actual contest, which is an amazing system and helped us a lot. Many thanks to Mike Mirzayanov and the whole team.

Edit 1: The registration is opened now, you can register here: http://mirror.codeforces.com/gyms

Thanks, Ahmed Aly

I'm trying to solve this problem: http://www.codeforces.com/problemset/problem/7/D

And here is my solution: http://www.codeforces.com/contest/7/submission/2865747

My code might look little bit ugly, because I tried to optimize it as much as I can, it's linear solution but it's getting TLE. Why is the time limit so strict like this? Is there any optimizations I can make? I think my solution is the intended solution.

Edit: I got it accepted after pre-computing all the powers instead of using my power function.

Something I noticed in many Codeforces contests, the less rated author makes harder problems. Did anyone else notice this?

I think this is because the low rated authors underestimate their problems, and maybe this is happening because they are trying to think like the high rated coders to make sure that the problems are not too easy for them, which makes the problems hard even for the high rated coders.

If you think this is happening, what do you think are the reasons for this?

I can't register in this contest.

I love any contest with the ACM-ICPC rules, and I'll love it more if it's rated for Div. 1 also. Please make it rated for Div. 1 also.

1- 916852: 509
* 67th in Codeforces Round #137 (Div. 2): +139 (from 1553 to 1692)
* 10th in Codeforces Round #138 (Div. 2): +78 (from 1692 to 1770)
* 87th in Codeforces Round #140 (Div. 1): +103 (from 1770 to 1873)

2- MinakoKojima: 500
* 67th in Codeforces Round #138 (Div. 1): +121 (from 1772 to 1893)
* 23rd in Codeforces Round #140 (Div. 1): +129 (from 1893 to 2022)

3- gchebanov: 468
* 25th in Codeforces Round #138 (Div. 1): +105 (from 2009 to 2114)
* 7th in Codeforces Round #140 (Div. 1): +99 (from 2114 to 2213)

4- azizkhan: 459
* 11th in Codeforces Round #138 (Div. 1): +139 (from 1914 to 2053)
* 50th in Codeforces Round #140 (Div. 1): +61 (from 2053 to 2114)

5- bayleef: 422
* 17th in Codeforces Round #138 (Div. 1): +103 (from 2058 to 2161)
* 13th in Codeforces Round #140 (Div. 1): +81 (from 2161 to 2242)

You can check how are the above scores calculated here: http://mirror.codeforces.com/blog/entry/5169