Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. Round #10 will take place on Saturday, Aug/06/2016 11:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous rounds, this will be a Div1 + Div2, with 7 tasks of varied difficulty. We are honoured to have Yury_Bandarchuk as a problem setter.

This round is going to have some money prizes, as follows:

• First place: 125$
• Second place: 100$
• Third place: 75$
• Fourth and fifth place: 50$
• Two more special prizes, each consisting of 50$. The criteria for the special prizes is not chosen yet, but we will make it public after the contest.

Also many thanks to HellKitsune for translating the tasks in Russian.

Platform changes since Round #9:

• Added auto-complete to the editor
• Worked on cross-browser compatibility
• Added C# support
• Small UI improvements

Contest format:

• You will have to solve 7 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

Hello Codeforces!

The latest csacademy contest, Round #9 took place on Tuesday, July/26/2016. First of all congratulations to the winners:

1. FatalEagle
2. uwi
3. anta
4. tourist
5. I_love_Tanya_Romanova

In addition to the top 5 finishers, we initially announced that we're going to have 2 more special prizes. Meanwhile we changed our mind and decided to have 3 special prizes:

1. The first special prize is awarded to snuke, for being the first one to solve Sum of Squares, which proved to be the second hardest problem after Jetpack.
2. The second special prize is awarded to Kostroma for a correct solution at Jetpack that unfortunately got TLE.
3. For the third special prize, we decided to assign weights to all the contestants who solved at least one problem, but were not among the top 5. The contestant placed 237th had a weight equal to 1, while the one placed 6th had a weight of 5, with everyone in between linearly distributed. Using these weights we randomly chose the winner: anubhav94.

All the winners, check your email for more details about collecting the prizes.

This round was special for us, as we had the first external problem authors. Thanks again to enot110 and mgch for authoring Jetpack and 101 Palindromes. Also, Yury_Bandarchuk did a great job translating the statements in Russian. To our big surprise, there were 248 users who submitted at least one solution. Even though it's not much, for us it was a record breaking number. We hope you had fun participating and we hope to see you all again at Round #10.

Unfortunately though, not everything went smoothly, as we encountered some issues:

1. The website froze 50 minutes into the contest for about 10 minutes. This was due to a bug on our side that got fixed :).
2. The dynamic scores were not calibrated properly. The first 4 tasks all got a final score of 100 points, with a huge gap between them and the last 3. Maybe the set was not that balanced either, but we're learning from every mistake. We are still waiting for our user base to grow a bit more before introducing divisions. The format of the contests will then change, with 4 tasks to be solved in 100 minutes.
3. The time limits were too strict for some of the problems. Usually we set it to be twice the running time of the official implementation, but when there's no obvious brute force in sight we should be more generous.
4. Finally, as you could notice after the contest, FatalEagle's solution for Jetpack had some hardcoded input values. Given that we have full feedback there's no way we can stop this from happening again. One can always binary search the input values using the judge message: TLE if N <= some fixed value, MLE otherwise. Sure, there are some quick fixes like not showing as much feedback as we currently do, but we don't want to change the system yet. The long term plan is to implement pretests, so this kind of hack can be avoided completely. Until then though, a line needs to be drawn somewhere. So from now on, we reserve the right to delete a submission that got AC if we can find a test respecting the constraints that makes the solution fail. Of course, this doesn't apply in the case of weak tests on our side, or some legit randomised solutions. We just want to make sure nobody "games the system" in the future.

That being said, we had lots of feedback from you guys and we already started working on everything. Thank you all!

Hello, Codeforces!

For the past week we've been working on adding multi-language support to our website. We've already started adding Russian translations with the help of HellKitsune. We wish to thank him publicly for all the help he's provided.

Now we are looking for trust worthy volunteers willing to translate the past problem statements and the interface in other languages. If you want to help write us an email at [email protected] or leave a comment here.

Thank you all!

Hello, Codeforces!

We continue the series of contests dedicated to IOI 2016 with IOI 2016 Training Round #4. We will again use problems from past Romanian competitions. For this reason, the round will be unrated.

The contest will take place on Saturday, July/09/2016 11:00 (UTC). This round's difficulty will be similar to the previous ones. Don't forget to register in order to participate.

Contest format:

• You will have to solve 3 tasks in 3 hours.
• There will be full feedback throughout the entire contest.
• The tasks will have partial scoring. The maximum score for each problem will be 100 points.
• There will be no tie breaker, so two users having the same total score at the end of the contest will share the same place in the standings.

The problem authors for this round are Adrian Airinei, Cosmin Gheorghe and Mihai Pătrașcu.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial has been posted. Congratulations to the winners!

Check out this problem. You can leave your comments here or on our blog.

Hello, Codeforces!

We have recently launched an online diff tool. It can be really helpful when trying to figure out changes in two versions of the same file, or when comparing outputs given by two different programs.

For any feedback, leave your comments here :).

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. Our Beta Round #8 will take place on Saturday, July/02/2016 16:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous rounds, this will be a Div1 + Div2. Due to the feedback we've got during the past couple of weeks we decided to change the format, by adding an extra easy problem. So this round will consist of 7 tasks of varied difficulty.

Platform changes since Beta Round #7:

• We redesigned the homepage. It now includes a global chat, latest blog entries, future contests and top leaderboard.
• We launched a new lessons section:

1. Introduction to graphs
2. Breadth first search
3. Stack Introduction
4. Stack Application: Soldiers Row

• We introduced a new markup language for the chat.
• We added emoticons to the chat.
• We added latex to chat.
• We launched a graph editor tool.
• We added voting for comments.
• We added a new user colour.

Contest format:

• You will have to solve 7 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The ratings have been updated and the editorial has been published.

Hello, Codeforces!

We have recently launched a graph editor tool. Feel free to use it whenever you want to visualise or create a medium size graph. It currently supports up to 30 nodes.

For any feedback, leave your comments here :).

Hello, Codeforces!

We continue the series of contests dedicated to IOI 2016 with IOI 2016 Training Round #3. We will again use problems from past Romanian competitions. For this reason, the round will be unrated.

The contest will take place on Friday, June/24/2016 14:00 (UTC). This round will be a bit harder than the previous ones. Don't forget to register in order to participate.

Contest format:

• You will have to solve 3 tasks in 3 hours.
• There will be full feedback throughout the entire contest.
• The tasks will have partial scoring. The maximum score for each problem will be 100 points.
• There will be no tie breaker, so two users having the same total score at the end of the contest will share the same place in the standings.

The problem authors for this round are mugurelionut and Mihai Pătrașcu.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial has been posted. Congratulations to the winners!

Hello, Codeforces!

We continue the series of contests dedicated to IOI 2016 with IOI 2016 Training Round #2. We will again use problems from past Romanian competitions. For this reason, the round will be unrated.

The contests will take place on Thursday, June/16/2016 13:00 (UTC). The difficulty will be medium, similar to the previous round. Don't forget to register in order to participate.

Contest format:

• You will have to solve 3 tasks in 3 hours.
• There will be full feedback throughout the entire contest.
• The tasks will have partial scoring. The maximum score for each problem will be 100 points.
• There will be no tie breaker, so two users having the same total score at the end of the contest will share the same place in the standings.

The problem authors for this round are Cosmin Silvestru Negrușeri, mugurelionut and wefgef.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial has been posted. Congratulations to the winners!

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. Our Beta Round #7 will take place on Sunday, June/12/2016 09:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous rounds, this will be a Div1 + Div2, with 6 tasks of varied difficulty.

Platform changes since Beta Round #6:

• We added a new comment section/task.
• We added a new editorial section/task.
• We started working on rewriting the editorials and also adding official implementations to the articles.

Contest format:

• You will have to solve 6 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The ratings have been updated and the editorial has been published.

Hello, Codeforces!

As IOI 2016 is around the corner, we decided to host a series of competitions in a format more similar to the Olympiad. We will use problems from past Romanian competitions. For this reason, the contests will be unrated.

IOI 2016 Training Round #1 will take place on Sunday, June/05/2016 09:00 (UTC). This contest will have a medium difficulty, but we hope you'll find the tasks interesting. Don't forget to register in order to participate.

Contest format:

• You will have to solve 3 tasks in 4 hours.
• There will be full feedback throughout the entire contest.
• The tasks will have partial scoring. The maximum score for each problem will be 100 points.
• There will be no tie breaker, so two users having the same total score at the end of the contest will share the same place in the standings.

The problem authors for this round are Cosmin Silvestru Negrușeri, mugurelionut and Mihai Pătrașcu.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial has been posted. Congrats to everybody who got a maximum score!

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. Our Beta Round #6 will take place on Tuesday, May/31/2016 16:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous two rounds, this will be a Div1 + Div2, with 6 tasks of varied difficulty.

Platform changes since Beta Round #5:

• We added virtual contests. Now you can simulate a past round easily with a single click in the contests page.
• Contestants source code is now public. Go to any scoreboard and click on a check mark.
• The online editor now support an "Open file" button. No more copy paste when trying to submit.
• We added some useful shortcuts to the editor. Hover a button to see its shortcut combination.

Contest format:

• You will have to solve 6 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The ratings have been updated and the editorial has been published.

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. From now on we're going to have a competition every two weeks, so here we go:

Beta Round #5 will take place on Monday, May/09/2016 16:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous round, this will be a Div1 + Div2, with 6 tasks of varied difficulty.

Platform changes since Beta Round #4:

• IMPORTANT: When the contest starts the page will automatically load the tasks and open the first problem for you. Please don't refresh the page, as this will probably overload the server.
• We fixed the editor buttons bug. Now you can safely compile and run your code in the editor with no fear of the buttons freezing.
• We changed the contests page to show local times (in addition to UTC).

Contest format:

• You will have to solve 6 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We are curios to know how many of you use the online editor we provide. Let us know in the comment section below. Suggestions and feedback will be highly appreciated.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial is ready. Congratulations to all the users and we hope you had a great time. We are waiting for you at Beta Round #6 in two weeks.

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. Once again we'd like to thank all our users for the great feedback they provide. We try to listen to your advice and improve our platform with each competition.

Our Beta Round #4 will take place on Tuesday, Apr/26/2016 16:00 (UTC). If you want to take part in this round you need to register before the contest begins. You can access the chat room for this round here (login required). Initially we were planning on having two divisions starting with this round. After taking a closer look at the rankings we decided it's too early to separate our users. So this round will be a Div1 + Div2, with 3 easy tasks and 3 more challenging ones.

Platform changes since Beta Round #3:

• We have integrated our rating system and retroactively applied it to the previous three rounds. You can access the rankings here. For each round we considered only those users who submitted at least one solution. If you registered but didn't submit anything your rating should've been unaffected.
• We have created profile pages. Important: You need to have a username set in order to access your profile page. If you want to use your Codeforces handle you need to link your account in the account settings page.
• For those of you who linked your CF account we used our charts library to plot the CF rating. If you didn't link your account you can check out what it looks like here, under the "External profiles" tab. The charts support zoom and drag behaviours.
• We have added global chat rooms for the contests. The chat room will be available only before and after the round takes place. During the contest we will deactivate it.

Contest format:

• You will have to solve 6 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic scores. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

We still recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial is ready. Congratulations to all the users and we hope you had a great time. We are waiting for you at Beta Round #5.

LATER EDIT: We fixed the bug and updated the ratings

Hello, Codeforces!

We are happy to announce that we're going to host a new contest at csacademy.com. There were plenty of users who helped us by providing lots of feedback after the last round. We'd like to help everybody for their support :)

Our Beta Round #3 will take place on Tuesday, Mar/22/2016 17:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous round, the difficulty will be moderate (similar to a Codeforces Div. 2)

Contest format:

• You will have to solve 5 tasks in 2 hours.
• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic score. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tie breaker.

About the penalty system:

• Computed using the following formula: the minute of the last accepted solution + the penalty for each solved task. The penalty for a solved task is equal to log2 (no_of_submissions) * 5.
• Solutions that don't compile or don't pass the example test cases are ignored.
• Once you solve a task you can still resubmit. All the following solutions will be ignored for both the score and the penalty.

Platform changes since Beta Round #2:

• Personalised source templates for when you open a new task (access them in your account settings, the worskspace tab)
• Workspace UI clean-up (Compile/Run/etc buttons are grouped together)
• Workspace settings persist when you load the workspace again and apply to all workspaces (font size, editor theme, etc)
• Clean-up some g++ compiler warnings (to ignore scanf return values)
• Stderr output was not being updated correctly sometimes
• Backspace key was not working in some circumstances
• Slight performance tweaks and some other small bug fixes

Unfortunately we didn't have time to fix the browser compatibility issues, so we recommend using an updated version of Google Chrome. If you find any bugs please email us at [email protected]

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial is ready. Congratulations to all the users and we hope you had a great time. We are waiting for you at Beta Round #4.

Hello, Codeforces!

We are glad to invite all of you to test out our new Online Judge platform at csacademy.com. We're a Romanian based start-up that focuses on online education. Up until this point we've been working on creating a new environment for competitive programming contests.

Our first beta round took place in January and it was an IOI-style contest of medium difficulty. You can have fun solving the problems in our archive. Pay attention though, it is necessary to have an account in order to solve any problems on our website. You can connect via Facebook or Google+, or you can simply create a new account by providing a valid email address. Once you have an account you can choose a username, but all Codeforces handles are already reserved (so no tourist for the locals :D). We have created for you the possibility of connecting your Codeforces user here. Once connected, your Codeforces handle becomes available, otherwise it stays reserved for an indefinite amount of time.

Our second beta round will take place on Friday, Mar/04/2016 17:00 (UTC). If you want to take part in this round you need to register before the contest begins. Just like the previous round, the difficulty will be moderate (similar to a Codeforces Div. 2). You will have to solve 6 problems in 2 hours and 30 minutes.

This time around the format of the round will be different:

• There will be full feedback throughout the entire contest.
• Tasks will not have partial scoring, so you need to pass all test cases for a solution to count (ACM-ICPC-style).
• Tasks will have dynamic score. According to the number of users that solve a problem the score will vary between 100 and 1000.
• Besides the score, each user will also get a penalty that is going to be used as a tiebreaker. The penalty is computed taking into account the minute of the last accepted problem and the number of wrong submissions (only submissions for accepted tasks count).

More about our platform:

• For the best user experience we recommend using Google Chrome. We are still in beta and we didn't have time to check if everything works on other browsers.
• We currently support C++14, Java8, Python2 and Python3. We recommend using only C++ and Java for a contest, as the time limits are not calibrated for Python.
• We have a pretty cool online editor. We use it ourselves, so give it a try ;)

If you find any bugs please email us at [email protected]

People currently involved with CS Academy include:

• Mikester
• AndreiNet
• alex.velea
• Kira96
• gheorghemihai
• wefgef
• mihaic
• vladb

Don't forget to like us on Facebook, VK and follow us on Twitter.

EDIT: The editorial is ready. Congratulations to all the users and we hope you had a great time. Beta round 3 is around the corner, keep your fingers crossed!

EDIT2: We're hosting Beta Round #3.