The recent testing round went well. It is expected that everything will run faster. Today's round was prepared by: Mike Mirzayanov, Nickolay Kuznetsov, Ivan Fefer and Maria Belova.
Artem Rakhov and Codeforces team
Tired to rest? Your help is needed.
During the period from December 31 until today I have made many changes in the Codeforces. The changes affected only the interior, so you will not notice any change in the user interface. Nevertheless, during this time was changed about 150 project files, database schema, some principles of data storage. In short, after all this, I'm not sure that everything works as expected (although, of course, I spent time on testing). For this reason I decided to organize Codeforces Testing Round #1, which will unrated and his only goal - a comprehensive testing of the project in conditions close to the real contest.
It will be three problems (possibly well-known, folklore), but I hope it will be pleasure to solve them.
Thanks for the help to Artem Rakhov, Maria Belova, and Max Ivanov
UPD: Thanks to all. The round finished. We didn't notice any bugs. Write suggestions and opinions in the comments.
Happy New Year, Happy New Code!
Let the new year bring you not only the traditional happiness, luck and health, but little programmer's delight: complete solutions, advance of (semi)finals, rating increase and absolutely no need to debug because of the perfect code. Wish you beautiful ideas and implementations!
It is usual to make presents On New Year. I do not know, what can you prepare for Codeforces (problems? articles?), and we decided that on New Year's sometimes happens what does not happen on other days. In the New Year holidays (from 31 December to 3rd January) in the user interface (Profile -> Settings -> handle) you can change your handle to any other.
Have fun celebrating the holiday,
P.S. Thanks to anatoly-rr for such a beautiful calendar.
Problem A: Answer is floor(N*M*0.5). Since there is N*M cells on the board and each domino covers exactly two of them we cannot place more for sure. Now let's show how to place exactly this number of dominoes. If N is even, then place M rows of N/2 dominoes and cover the whole board. Else N is odd, so cover N-1 row of the board as shown above and put floor(M/2) dominoes to the last row. In the worst case (N and M are odd) one cell remains uncovered.
I am happy to tell you that Codeforces will soon free you from reading those endless "Please, give me test #??" in the comments. Now you can click on a link with the submission-id on the status page and it will show not only the original solution texts, but also the tests on which testing was performed (the judging system report). It will not contain the full inputs/outputs/answers if they are too large – you will have to wait for now and enjoy their prefixes. As soon as we understand that there're no bugs in the implementation, we will open all the previous contests to view the tests.
However, that is only the first step; later you will be able to download contest problem archives that will contain full texts (or their generators) as well as the authors' solutions and other materials.
Of course we do not want Codeforces problems to be copied from one "online judge" to another one. You’ve got to understand that Codeforces puts huge effort into preparing tasks and organizing contests. That's why we limit the material usage to make using our problems on websites or in other automatic testing systems impossible. On the other hand, we will be glad if the contest materials will be useful for individual training or for some assemblies, training sessions etc. with the onsite participants. Read the license text carefully as we want some Codeforces data to be published near (or inside) the problem tasks.
At the moment it is version 0.1 of the license, we will perhaps change a lot in it, but I guess the idea will undergo no changes.
Codeforces materials usage license (v. 0.1)
One more codeforces format round takes place this evening. I'm the author of the contest problems. Artem Rakhov and Maria Belova helped me to prepare the problems. Great thanks to them and all codeforces "fighters"!
I wish you good luck and funny hacks!
P.S: This round won't be rated. So your ratings won't change. That's because of severe problems with codeforces server. Read here for explanation.
Soon many of you will have your examinations, and someone even have it now. I wish you excellent marks and many easy exams!
Artem Rakhov and Codeforces team