The Balkan Olympiad in Informatics 2018 (BOI 2018) takes place between the 7th and 13th of July 2018, in Timisoara, Romania.

The official site of the competition can be found here.

Let's discuss the tasks after each contest day.

# | User | Rating |
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1 | Benq | 3797 |

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5 | ksun48 | 3463 |

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7 | maroonrk | 3446 |

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5 | SecondThread | 176 |

8 | -is-this-fft- | 175 |

9 | Um_nik | 171 |

10 | antontrygubO_o | 167 |

The Balkan Olympiad in Informatics 2018 (BOI 2018) takes place between the 7th and 13th of July 2018, in Timisoara, Romania.

The official site of the competition can be found here.

Let's discuss the tasks after each contest day.

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Can you provide tasks from 7th july ?

Tomorrow is the first day of competitions, both for junior and senior teams.

Will there be a mirror?

No.

Will there be live standings at least?

Check these links later:

http://boi2018.ro/competition-tasks

http://boi2018.ro/competition-results

Competition must have started, does anybody have a clue if there will be a livescore? Can't find any on the website.

There is no public livescore.

Unfortunately, there is no public scoreboard, but here is a snapshot if anyone is interested: Current results

Keep us updated please

Sure I will, but nothing much is changing: Results

Thank you so much! Does it take the best submission? Also could you try to update it from let's say 30 mins in 30 mins? That would really help. I don't see if you have the rankings why can't they just make them public though...

Takes last submission, not best — at least that's what I got told.

The System is not CMS so maybe it doesn't support broadcasting rankings as easily. Just guessing, though

It doesn't take the best submission, it takes the last one, so the standings aren't always the best ones. I'll try to update them every 30 minutes. And for the rankings, the committee's 'excuse' for that is that something is going to crash if they make it public. I can publish the tasks if you want.

Can you publish the tasks, please?

I don't have English version of printed tasks, but I can write a brief description of tasks.

minmaxtree: We are given a tree of size N (N <= 10^5 or so), and we should reconstruct the tree (weights of every edge) in order to fulfill M (M <= 10^5 or so) constraints of type MAX u v x, meaning that the maximum of all the edge weights on simple path from node u and node v is equal to x, and MIN u v x, meaning the same thing but for the minimum.It's guaranteed that the answer will always exist.

electionsGiven a string of 'C' and 'T's (of length <= 10^5) , we should answer Q (Q <= 10^5) queries of type L R. Answer to the query is the minimum number of removals to make interval [L, R] good. A good interval is defined as an interval in which there is no prefix or suffix containing strictly more 'T's than 'C's.homecomingWe are given a circular list of N (N <= 10^5) books, each having cost A_i. Also, for every consecutive interval of size K (exactly N of them), we are given a prize we get if we buy them all. We are asked what is the highest amount of money we can get.This is just a brief overview, I may have made some mistakes and if I have, sorry for that. Also, the constraints aren't exact, but they are between 1e5 and 1e6 for every task so it doesn't matter much.

I'd like to hear your solutions.

Thanks!

I can only post them in Serbian, I guess that won't mean anything to you :)

Upd: link

Upd: First two Romanians scored 200, milisav scored 100 on first problem, nothing apart from that in top 10 has changed.

Upd: link

Upd: TadijaSebez solves elections and claims the third place!

Update: results

Results, half an hour before the end

Can you please also give a picture with the final results (maybe for juniors as well)? Also thanks for keeping us updated:)

Day 2 have just started, I'll try to be publishing tasks & 'live' results once again

Soo could you try to give a Ss in the near future? Also please don’t forget about juniors: maybe you could give a picture per hour for them instead of per 30 minutes if that’s not too hard? We thank you for your service:))

Sure thing, there it is. JBOI current results: https://screenshots.firefox.com/teeI3PzT4Jg9rphX/192.168.100.3 BOI current results: https://screenshots.firefox.com/b8lv6MzI9Zgl2hg7/192.168.100.3

JBOI current results: https://screenshots.firefox.com/AQCNDA8HsxkJZ14s/192.168.100.3 BOI current results: https://screenshots.firefox.com/zjzpdppKWN6r10By/192.168.100.3

JBOI results: https://screenshots.firefox.com/fgQvAThSXtKM0UFm/192.168.100.3 BOI results: https://screenshots.firefox.com/qMzGlIMZKHIeOPiE/192.168.100.3

Can you give one last update before the end?

BOI at 13:10.

Final BOI results, photo by perchema. GG, petrescu.

What about JBOI results, can somebody post those?

JBOI results (current): link

Hi. You can find the statements here:

https://drive.google.com/drive/folders/19d7eX7JqE6ikBEwf8cG0mqS8NfSdR4QP?usp=sharing

Enjoy :)

You can also see the standings in the link i provided above.

Can you also provide a screenshot for the JBOI?

Done.

Can you share JBOI tasks, please?

Given N and K, find sum of all the numbers strictly less than N having exactly K ones in its binary representation. N <= 10^15

Given N, find sum as an irreducible fraction . Output P and Q.

Given a set of N <= 10^5 non-intersecting (and non-overlapping) rectangles with sides parallel to coordinate axes, and having coordinates between 1 and 10^6, answer Q <= 10^5 queries of kind: Find the sum of the lengths of intersections of a ray with every rectangle in the set, where every ray is starting from some point at x-axis and forming an angle of 45 degrees, 90 degrees, or 135 degrees with x-axis.

Tasks have been posted fyi: http://boi2018.ro/tasks-jboi

Day 2 (tasks + results):

https://drive.google.com/drive/folders/1I-IFJDKPsxKNHxRdMrHnmmrdH93kZI7F?usp=sharing

Can you also add the JBOI ranking?

I don't have access to it. I'll ask the JBOI committee later.

http://store.picbg.net/pubpic/C1/C2/b1b0124607e6c1c2.jpg

There are people from Turkmenistan in the results table. But Turlmenistan isn't a Balkan Region country.

How other countries (not from Balkan region can participate in this contest)?

Look at the rules, they can be invited but they aren't official participants IIRC.

This year they wrote to the organizing committee, and this is what any country can do in any year. BOI (as well as CEOI, from what I know) is open to inviting new countries, only that they are considered unofficially

What happened to Turkish team? They're in the participant list but none of them in standings.

Our team's leaders' passport issuances were delayed due to bureaucratic reasons. So sadly we couldn't attend this year's Balkan Olympiad.

Our poor country...

Does anyone know of a judge where you can submit the problems which have a special checker (minmax tree for example)?

And have the official checkers been published?

They haven't been posted on the official website, but we don't mind sharing them with anybody who wants to add them to an online judge.

And I spend almost an hour yesterday writing my own checker :/

Why not make them public? It would be a great help. Because we had an idea of simulating the competition but nobody wanted to write the checker :D

I have a question: the tests for the task popa seems obfuscated. Can you provide testcases in a normal format or tell us how we can extract them ourselves?

I didn't write the grader, but afaik the format of the grader is:

Each of the tests is described as follows:

Where X is the number of prime factors of the numbers (usually around 10). S is then given by:

S[1] = 2^{exp1[1]}·3^{exp2[1]}·5^{exp3[1]}·...S[2] = 2^{exp1[2]}·3^{exp2[2]}·5^{exp3[2]}·...And so on.

Thanks! It works with one exception:

S[i] = 2^{1000000 - exp1[1]}·3^{1000000 - exp2[1]}·...for some reason :P

The input is as Andrei1998 said. It is not necessarly to think it as gcd. There could be lcm or other such operation as well.

I will upload the grader to the BOI official website shortly.

How many contestants won a medal?

The only information I have at the moment is that at least 22 participants (including the unofficial participants) won a medal in the JBOI. The ceremony was held, yet there are no final standings with medals on the site.

You can submit

the problems from BOI 2018 here: https://oj.uz/problems/source/352allSince checkers, interactors and graders are entirely written by us, they could contain some bugs. If you spot one of them (if they exist :p), please notify us :D

Auto comment: topic has been updated by Andrei1998 (previous revision, new revision, compare).