Andrei1998's blog

By Andrei1998, history, 2 years 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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2 years ago, # |
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Can you provide tasks from 7th july ?

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2 years ago, # |
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Will there be a mirror?

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2 years ago, # |
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Will there be live standings at least?

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2 years 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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2 years ago, # |
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What about JBOI results, can somebody post those?

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

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2 years ago, # |
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Can you share JBOI tasks, please?

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    2 years 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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2 years ago, # |
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2 years 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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    2 years ago, # ^ |
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    Look at the rules, they can be invited but they aren't official participants IIRC.

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    2 years 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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2 years ago, # |
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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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    2 years 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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2 years 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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    2 years 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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      2 years ago, # ^ |
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      And I spend almost an hour yesterday writing my own checker :/

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      2 years 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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      2 years 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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        2 years 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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          2 years 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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            2 years 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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2 years ago, # |
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How many contestants won a medal?

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