Hi friends!

My name is Costin-Andrei Oncescu. I began preparation for the IOI in 2011, lasting for 8 years and culminating in one silver and two bronze medals. I began the journey being the first one in my region and not having access to much formalized training. Now in college, I reflect on my experience and come to realize how fortunate I am for all of the great lessons IOI taught me.

I now seek to pay it forward by bringing this experience to others that dare to be the first in their town, state, or country. In collaboration with other IOI medalists (Reyna, reedef, zscoder, Adhami, Rezwan.Arefin01, Bruteforceman, RestingRajarshi, AsleepAdhyyan), teachers, community organizers, and government officials, we are starting a project, CSPrep.org. This initiative is directed to ignite the first generation of IOI medalists in emerging countries by bringing access to dedicated mentors, curated resources, and quality instruction. Talent is global and deserves to be propelled to compete at the IOI from any corner of the world.

How can you get involved? Become a mentor.

How it works:

• You are assigned to 3-4 pre-selected, high-achieving students from an emerging country.

• You meet virtually with the group (at least one hour per week) to give advice and answer questions.

• You hold one-hour seminars periodically (bi weekly or once a month) covering a technical subject.

• You build an ongoing relationship with each of your mentees during the length of their preparation.

What are we looking for?

• You have been involved in competitive programming, including but not limited to IOI, or you have a rating of over 2100 on CodeForces.

• You care about helping great talent get started on preparation for IOI.

• You can devote at least one hour per week to the project.

Benefits for you:

• You do meaningful and highly-regarded volunteer service.

• You build life-long relationships/friendships with highly talented students.

• You gain instructional and leadership skills, which are highly valued in the market.

Please visit our site (CSPrep.org) to learn more and sign up! Feel free to share information about the project with anyone you know would be a good match and DM me if you have any questions.

Thanks for your time!

P.S. We have benefited from the internet, we have benefited from the work of those before us and now we would like to pay it forward and we hope you will consider joining us in empowering and training the next generation of competitive programmers.

Hi!

3rd edition of Info(1) Cup will take place this weekend. More information on the site. I'll make this post shorter than usual, if you want extra details, you can just check one of the posts from last years (here or here).

This year, we'll have official teams from 27 countries taking part to make this contest memorable. We dedicate this edition in the honor of Mihai Patrascu, one of the greatest Romanian Computer Scientists.

We hope that this edition will be even more fun and challenging than the previous ones. You can practice on past problems on oj.uz. This should give a good idea of the kind of level you could expect from the contest although we try harder and harder to make up more interesting and challenging tasks.

We invite you all to join the online mirror of either of the rounds (the national round, approximately div2 level, and/or the international round — CEOI/BOI/APIO level)

I invite you all to discuss ideas for the problems and give feedback after the ending of the online mirrors.

Good luck, should you choose to compete!

The online mirror is now over. Let's discuss the problems! Please, give us some feedback

Hi there!

As you all are aware, IOI 2018 is now over, and I felt the need to write a few lines about it, about my experience of it, and about my conclusions. I don't normally do that, but this was my last IOI and likely the end of my intense CP career.

So, the problems were absolutely great! Big up to the scientific committee. However, I'm sort of addicted to the codeblocks debugger which ruined the whole experience for me. As a matter of fact, the only reason for which codeblocks remained my primary editor was because its debugger was awesome and the only alternative of a better editor that I saw (better on the long run, including future real-life programming experience) would be vim which I knew is not even close to as friendly when it comes to user friendliness of debugging. I've also had competitions on a regular basis for 7 years and never had a time interval where I could say: well let's try something new cause we don't have anything useful to do (as I would always tell myself that it's better to train on thinking than on getting to know anything else — even the basis of relatively useful stuff). It was also the fact that I was very familiar with codeblocks after using it for soo long.

Hi!

Does anybody know if this year's edition of Mujin is supposed to be open internationally? Like will international participants be eligible for prizes and will the tasks be in English? I really liked last year's edition, but considering there was no blog about it and right now its description is fully Japanese, I tend to think that this year's edition might be Japanese-only...Can someone confirm this?

Hello everyone!

I'm happy to invite you to take part in the second edition of InfO(1) Cup, an online contest meant to be similar to international olympiads such as IOI, CEOI, BOI, APIO, etc. If you remember last year's entry about the contest, you should notice that we've been talking about making it an onsite event, but we decided it's both easier (especially financially) and helpful to more people (as we can have more online participants) to have it online.

The contest consists of 2 rounds: the national round and the international round. Participation in both rounds is invitation based (you can see the "official" participants here). We've tried to reach out to the official organizers of Informatics Olympiad in several countries to make the competition as fierce as possible by having future IOI-participans, as well as to help those students in their training for upcoming international olympiads.

Both rounds will have online mirrors (which are the purpose of this entry), that you're all invited to take part in. Both online mirrors will be taken in the usaco format. The first round is similar in difficulty to a div2 contest, 5 problems in 4 hours, whereas the international round (the one meant to be similar to IOI, CEOI, etc) will last for 5 hours and participants will have 4 problems to solve. If you are a strong participant, then we advise you to take part in the international round and if not, both rounds should be a good training.

The registration button for the online mirrors will become available at the beginning of the online mirrors (keep in mind that you can choose whatever 4 or 5-hour slot you want, you'll have several days to choose from for round 2, and only one for round 1). I will update the blog with the link to the registration button as soon as possible. You can take the first online mirror during this time interval (we will keep the online mirror of round 1 after the one of round 2, and will reupdate the blog with the exact time), and the second one will start at this time and last for 72 hours. As in the case of all contests with this format, we kindly ask the participants not to discuss the problems until the end of both the official round and its online mirror (may it be the national or international round).

The online mirror of the international round is now over. You may now discuss the problems. Please give us any sort of relevant feedback in order to improve the next editions.

The online mirror of the national round (round 1) has now started. You may now choose any 4-hour frame to take it. It will end in 2 days and a half or so (better check the link). Remember that this one should be similar to a div2 in terms of difficulty, although the format is pretty different.

You can check last edition's problems and rankings here.

And last but not least, I want to present the scientific committee (in random order): I (Costin Oncescu), Alex Tatomir (one of last year's winners of InfO(1) Cup), Alexandru Niculae, Costin Tudor, Cristea Theodor

Hello everybody!

I know that I've updated my first blog regarding Info(1) Cup a lot of times and I might already seem annoying. Well, the fact is that the first blog's main point was registering new countries in the competition and introducing it. This new blog is for those that might not have seen my updates regarding the online mirrors:

For about 1 day from now on, you'll be able to take part in any 5-hours frame that you wish in a virtual contest in the exactly same conditions as the official participants had. We find the problems really interesting and we challenge you to solve them all. I'm sure that taking part in this contest should be a positive experience for everyone, so I invite you to participate. The contest is OI like (with partial score based on subtask) and includes an interactive task. You can register and find the link of the contest here. The live scoreboard is on. The live scoreboard does not properly work. You may not appear right now on it, but stay calm, after we give it a refresh, you will. We'll do that at least once after the ending, so that all participants will appear in the final rankings and maybe few more times till the then.

LE: We've extended the duration of the online mirror by one day.

I have just been asked whether we'll have proper editorials. The answer is a categorical YES, they'll be published on the official site

Only a day left from the online mirror. Also, take care at the announcements on the interface, they are really meaningful

Hello everyone!

I'm writing this entry to invite you all to take part in the first edition of Info (1) Cup contest. It is an individual contest with algorithmic tasks and we will accept only C++ sources. The contest itself has 2 parts, both of which held online.

You can still take part in the online mirror in any frame of 5 hours before time. We invite you all to participate. The tasks should be challenging for everyone The live scoreboard of the online mirror is on.

PS: As in all the other contests that have online mirrors, I kindly ask you not to discuss the tasks until all the rounds and their online mirrors end. After that, on the official site, you'll find the editorials of the problems.

The first one consists of a national contest in which only invited Romanians can take part and which should be easier. We haven't decided yet whether we'll host an online mirror of it or not and I'll update the post later with this kind of information. We will host an online mirror of round 1 too. We invite you all to take part. We assess the difficulty to be similar to that of a div2 round or even a little lower, so if you are div1 we strongly advise you not to take part in this round, but rather in the second contest described below

The second one is the international contest that I can assure you anyone can take part in. However, as we want the contest to be as similar as possible to international OIs (such as BOI, or CEOI), we want just participants from the official teams of different countries to sign up at the official version. We'll also have an unofficial second contest, similar to an online mirror which you can take in any 5-hours frame for a couple of days after the contest (usaco system). The official round will have a fixed frame . If you consider the time frame good for your country and the country is not listed below yet, I kindly ask you to PM me with information about how to contact any person that may be considered to be in charge with the selection of your country's teams for international competitions to give them the link to the official registration form. Ohh and about the unofficial registration, you'll be able to make an account soon using the official site (LE: Now you can register for the online mirror). The contest will be full-feedback and will use CMS, 5-hours long with 4 problems with all kinds of difficulty level.

Also, about the prizes, we'll award medals and certificates to the winners of the official round,

Ohh and forgot to mention the scientific committee: I'm one of the members together with Alex Niculae and Costin Tudor

The official round 2 is now over. Congratulations to all the participants and special congratulations for those who got a maximum score: Mahmoudian Bidgoli Arash (who finished after just 3 hours and 48 minutes), Alex Tatomir and Mishinev Encho . I hope you enjoyed the contest. Also, we're sorry that, at the 4th problem, we had a limit a little too large which let solutions intended to get 78 points to get a full score. We'd like to address special congratulations to the only contestant that solved the problem in the intended way (that we find pretty tricky and nice and will be explained in the editorial after the ending of the online mirror), Hossein Mohammad Nematollahi.

We kindly ask you not to discuss the solutions until the end of the online mirror. However, we'd be happy to receive any kind of feedback regarding the competition so that we can improve it the next year, doesnt't matter whether it's positive feedback or not.

Hello!

I've been wondering is there any way to see what we have upvoted or even downvoted recently? I remember some comment explaining a nice trick that I surely upvoted as I found it really interesting and that's all I remember about it. It was something containing frequencies and sort of a sqrt trick to reduce the memory. However, this is just a particular case, don't pay attention to it. The main idea for which I wrote this post is to ask whether there is any general way of finding out what you have upvoted, similar to seeing all your past comments. It would really be helpful for those trying to find some old comment or post that they just broadly remember about: having this option you could certainly find what you were looking for really fast. If it exists, please let me know. If not, then I think it is a nice idea that should be considered for further updates of the site or for some interested guys able and willing to build an extension to provide this kind of information.

LE: I found the comment I was talking about. However, this does not change the main purpose of the post.

Thank you in advance!

Hello, everybody!

I'm writing this entry for asking for your help. It is a special kind of task, that I like the most and, however, I can't say am very good at. I'm talking about output only problems, or tasks similar to them, or some sort of puzzle tasks. I'm talking generally about tasks that require generating something (maybe an array or a matrix) as a input to a source that is given in the statement explicitly or implicitly (maybe they don't give you the source but they want the number of pairs of indices with who-know-what property to be large or small) to generate a number as high or as low as possible (not necessarily minimum or maximum). The worst is that I don't have any example to give at the moment (I don't exactly remember any such problem or where to find it). I'll try to give a short example (not necessarily solvable): Generate an array with N numbers smaller or equal than M so that the number of values that can be obtained by summing some of the initial values (each can be used at most one time) to be as large as possible. And I want a solution to generate for N = 10 and M = 100 a set whose size will be 500 (this may be an output only problem), or I am simply giving you N and M as input and the scoring is computed someway to let a strategy get 100 points (it's not an optimization task like codechef long challenge ones). Something like if you get a size of NlogM you get 100 or who knows.

I'd also like to include in this category the problems that ask for generating something with a certain property (like paving a matrix with some sort of puzzle pieces for example). These two types of problems are not that linked, but both of them require constructing of something.

One more important thing: I want the problems to be solvable by determinist algorithms or proved probabilistical solutions. Also, I don't ask for you to know their solution, even though that would help, but just for the problems and after a while I hope I'll get them done, or if not, I think I'll ask either here in the comments or in some separate post.

I especially like these sort of tasks and I want to train to become able to solve more of them. But they are hard to find (usually because such problems have a very big variety of scores and wouldn't be good as ACM tasks and most of the competitive programming resources that I know are targeting ACM training, and also because, as you can see, I don't know what is their generic name, so I can't google it or even see wheter there is already such a topic). So I wanted to ask: do you know where to find such tasks? Every single link may help. I also hope that I'm not the only one who appreciate such tasks, so that the topic will not be helpful just for me. As soon as I remember those problems of this kind that I've seen, I'll edit the post and add some links.

As generating a covering of someway of something, I have a link to a problem in Romanian that asks for paving a matrix whose corners are cut, with L shape pieces. Even though the statement is in Romanian, you can check the sample to see what it's asking for.

LE: I remember one of the problems I was talking about. It is almost what I wanted to say through this post, but the best representative of this category, I guess, is the one mentioned by Um_Nik

Thanks in advance!

Hello! I'm writting hoping that someone may help me. I've implemented a problem (CF round 200, div1E) and as verdict I'm getting denial of judgement. Can someone tell me what to do? Is this my fault or is some sort of CF error? Here is the link to the problem. Thanks in advance!

Hi. I was wondering what are the selections systems for IOI in different conutries. As far as I know, in math olympiad you can find the tasks from national selection contests translated into English, and I want to know if there is any such place for the informatics one. Romania's tasks, for example, unfortunately, are not translated into English and official solutions are hard to find (still, the tasks are available for solving and can be found at this site, the problems which have on the "sursa" column the words "lot" and "seniori" in the "arhiva de probleme" section are tasks from our national selection contests, around 18 per year). What about you? Where can I find your national OI tasks (preferably with an oline judge)? Is there any place where we can find their official solutions? I think that the answers for this question will help a lot of the high-school students to improve their skills.

PS: Please don't forget, when answering the question, to say wheter there exists a place where we can find the tasks, preferably with an online judge, or not.

I've been thinking for about 2 months at a problem and I haven't manage to find a solution, so I've decided to ask for your help. The problem is pretty nice. It asks for the number of trees(2 trees are considered different if they are not isomorphs) with N vertices and diameter D. Here you have the link . It was given in Polish Algorithmic Engagements 2008 at the final round and as far as I know there are no written solutions for this kind of contest.