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Andrei1998's blog

By Andrei1998, history, 5 months ago, In English,

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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5 months ago, # |
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Can you provide tasks from 7th july ?

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    5 months ago, # ^ |
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    Tomorrow is the first day of competitions, both for junior and senior teams.

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5 months ago, # |
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Will there be a mirror?

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5 months ago, # |
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Will there be live standings at least?

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

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    5 months ago, # ^ |
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    There is no public livescore.

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    5 months ago, # ^ |
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    Unfortunately, there is no public scoreboard, but here is a snapshot if anyone is interested: Current results

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      5 months ago, # ^ |
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      Keep us updated please

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        5 months ago, # ^ |
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        Sure I will, but nothing much is changing: Results

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          5 months ago, # ^ |
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          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...

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            5 months ago, # ^ |
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            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

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            5 months ago, # ^ |
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            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.

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              5 months ago, # ^ |
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              Can you publish the tasks, please?

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                5 months ago, # ^ |
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                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.

                elections Given 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.

                homecoming We 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.

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                  5 months ago, # ^ |
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                  Thanks!

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                  5 months ago, # ^ |
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                  I can only post them in Serbian, I guess that won't mean anything to you :)

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        5 months ago, # ^ |
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        Upd: link

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        5 months ago, # ^ |
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        Upd: First two Romanians scored 200, milisav scored 100 on first problem, nothing apart from that in top 10 has changed.

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        5 months ago, # ^ |
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        Upd: link

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        5 months ago, # ^ |
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        Update: results

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        5 months ago, # ^ |
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          5 months ago, # ^ |
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          Can you please also give a picture with the final results (maybe for juniors as well)? Also thanks for keeping us updated:)

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    5 months ago, # ^ |
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    Day 2 have just started, I'll try to be publishing tasks & 'live' results once again

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5 months ago, # |
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What about JBOI results, can somebody post those?

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5 months ago, # |
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5 months ago, # |
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You can also see the standings in the link i provided above.

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5 months ago, # |
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Can you share JBOI tasks, please?

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    5 months ago, # ^ |
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    1. 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

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

    3. 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.

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5 months ago, # |
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5 months ago, # |
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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)?

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    5 months ago, # ^ |
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    Look at the rules, they can be invited but they aren't official participants IIRC.

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    5 months ago, # ^ |
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    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

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

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    5 months ago, # ^ |
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    Our team's leaders' passport issuances were delayed due to bureaucratic reasons. So sadly we couldn't attend this year's Balkan Olympiad.

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5 months ago, # |
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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?

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    5 months ago, # ^ |
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    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.

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      5 months ago, # ^ |
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      And I spend almost an hour yesterday writing my own checker :/

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      5 months ago, # ^ |
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      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

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      5 months ago, # ^ |
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      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?

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        5 months ago, # ^ |
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        I didn't write the grader, but afaik the format of the grader is:

        Maximum number of queries per test
        Number of tests (usually 5)
        Test 1
        Test 2
        ...
        Test 5
        

        Each of the tests is described as follows:

        N X
        exp1[1] exp1[2] ... exp1[N]
        exp2[1] exp2[2] ... exp2[N]
        ...
        expX[1] expX[2] ... expX[N]
        

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

        S[1] = 2exp1[1]·3exp2[1]·5exp3[1]·...

        S[2] = 2exp1[2]·3exp2[2]·5exp3[2]·...

        And so on.

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          5 months ago, # ^ |
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          Thanks! It works with one exception:

          S[i] = 21000000 - exp1[1]·31000000 - exp2[1]·...

          for some reason :P

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            5 months ago, # ^ |
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            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.

            An index i can be the father of index j if:
            
            exp1[i] >= exp1[j]
            exp2[i] >= exp2[j]
            ...
            expX[i] >= expX[j]
            
            This is the only thing the grader is based on.
            

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

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5 months ago, # |
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How many contestants won a medal?

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    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.

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5 months ago, # |
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You can submit all the problems from BOI 2018 here: https://oj.uz/problems/source/352

Since 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

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4 months ago, # |
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Auto comment: topic has been updated by Andrei1998 (previous revision, new revision, compare).