Hi Codeforces,

I hope you enjoyed the contest despite the difficulty. Do not hesitate to ask questions and discuss the problems here. :)

If you participated, I would really appreciate if you could fill in this short form. It only takes 1 minute and will be useful for my thesis. https://goo.gl/forms/XPfkoRxRjEKmTDt32

Editorial: https://vlecomte.github.io/set/geo18/editorial.pdf

Example solutions:

• A: https://pastebin.com/kr3jc1qZ
• B: https://pastebin.com/mhz6J0bW
• C: https://pastebin.com/JMdQg4Dr
• D: https://pastebin.com/bQUTXGG8

You can also download all solutions/generators/checkers/validators here: https://vlecomte.github.io/set/

Thanks to all who participated! :)

Hi Codeforces,

As I mentioned before, as part of my Master's thesis, besides my book I am organizing a contest with exclusively geometry problems to showcase some types of problems or techniques that I think could be cool to see in the future in ICPC and other contests.

It will take place this Sunday 08:00 UTC in the Gym (the link will be http://codeforces.me/gym/101793, registration should open 6h before and remain open during the contest). There will be 4 problems to solve in 3 hours.

The problem should be particularly relevant for students participating to the ICPC. But the problems will be very hard, so I think they can be interesting to everyone with a sufficient level in geometry.

The problems will be roughly sorted by estimated difficulty, but please read all the problems, as you might find that you feel more interested by one of the "harder" problems. The statements will be given all together in a PDF attachment. The samples will be in the PDF as well as on the problem pages.

Since it's my first time organizing a whole contest by myself, I hope everything will go smoothly. I would like to thank yunoac for the precious feedback on the tasks (and of course his amazing support during my whole thesis), Nicolas16 for beta-testing the problems in a tight schedule, and of course MikeMirzayanov for the great Codeforces and Polygon platforms.

I hope many of you will participate to the contest and enjoy the problems. See you for the editorial!

PS: You might want to revise your 3D geometry. ;)

UPD: The length is confirmed to be 3 hours. The contest will be held under ICPC rules. You can participate either individually or in a team.

UPD2:

Congratulations to the winners:

1. Team TooLazyToPropagate (hitman623, DeshiBasara, TooDumbToWin)
2. Hujiwara
3. aid
4. chemthan
5. Swistakk

who also happen to be the only participants to solve at least one problem.

Thanks to everyone for participating, the editorial is coming in a moment!

Hi,

I've updated my geometry book over at https://vlecomte.github.io/cp-geo.pdf. I hope you like the new content, and I would really appreciate any feedback: suggestions, comments, typos you found, etc. :)

The changes I made:

• Finished the chapter on "basics" and made some changes based on your feedback from last time.
• Added a whole chapter on precision issues and how to deal with them. I think some of the problems and ideas in this chapter are not obvious to all and I think they can be useful for people who don't feel very confident in geometry.

The codes are mostly untested for now so take them with a grain of salt (and tell me about the mistakes you find).

In a few weeks, I will hold a Gym contest showcasing geometry techniques/concepts that are not very common at the moment but could help make interesting problems and add some variation to geometry in ICPC-style or online contests.

There will be 5 problems for 3-4 hours. They will be hard but (I hope) interesting. After the contest, along with the editorial, my book will be updated to include all the topics that are linked to the contest. I will post an announcement as soon as the time is fixed. I hope many of you will participate. :)

UPD: I added a chapter on 3D geometry. As usual, feedback of any kind is very appreciated. It's probably full of errors. :)

Hello!

I'm writing a book on geometry with a competitive programming approach. I've just started, so I haven't written much at all yet but I'd like to have some early feedback.

My goal is to be easy to understand and practical (quite code-oriented), but also to explain important concepts in depth and try to build intuitions / interesting interpretations, because I think I can bring some things on that front. In what I've written I feel like the "in depth" part is okay but I'm afraid the "easy to understand" part is a bit lacking.

So far I've covered complex numbers, point representation, dot product, cross products and their applications, as the first part of a "Basics" chapter. There will eventually be other chapters, covering things like sweep algorithms, algorithms on convex polygons/hulls, and especially 3D geometry, which I like a lot.

I'd like to have feedback mostly on writing style and on ways in which I can make the explanations more accessible (e.g. adding examples, figures, rephrasing, etc.), but any comment or suggested improvement is welcome. I know I've not written much but there are some concepts in there which I found tricky to explain, so there should be plenty to criticize. :)

Here's the link (I'll update it as I fix things and add sections): https://vlecomte.github.io/cp-geo.pdf

Hi!

Next year I'll start working on my Master's thesis (in computer science), and we have to choose the subjects now. I'm not very enthusiastic about the subjects that are suggested by default but we are allowed to suggest our own topics if we want. So I got an idea: what if I could work on a topic related to competitive programming?

I have good relationships with some of the teachers so I should be able to convince one of them to accept it if it's an interesting subject. But it's not that easy to find a good subject on that theme.

An example I thought of would be to study the current state of the art in a subfield like geometry: which kinds of problems appear in which competitions, which algorithms are considered common knowledge, which kinds of implementations are used, how precision issues are dealt with, etc. I would try to summarize that and to figure out by reviewing the research litterature which new algorithms or techniques might appear in the future, thanks to which implementations.

So, do you have any ideas on interesting subjects to study? It can be about any aspect of competitive programming, also including coaching, contest creation, etc. I'm also a trainer for future IOI contestants and a novice problem setter so those subjects interest me too. I'm excited to hear your ideas!

Of course, if the subject gets accepted, I would keep you informed and post regular updates over here (your feedback would be a great help)!

Thanks in advance!