How were the ratings for April Long 2017 updated so fast? What optimizations were made by the CodeChef team?

How was the plagiarism check done so fast?

@admin any insights?


I dont think plagiarism detection was done this time. Many people have just copied the Dijkstra’s algorithm
for problem no 4 from geeksforgeeks.Sad :frowning:

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Well, even if people did copy the Djikstra’s algorithm, they wouldn’t have gotten more than 45 points. Its inevitable, when the concept of subtasks are given priority in long contests. Anyways, one of the best Long challenges in recent times, with so many solvable-yet-hard-to-think-of problems!Cheers to the Codechef team! :slight_smile:


I’m sorry, but has anybody got laddus for this round? Sorry, but it’s my first round and i don’t know,when you got them!

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The plagiarism test and the subsequent appeals process takes many days to get finalized. And we used to calculate the new ratings only after this was done.

Now, we have modified our process so that the ratings update will be done ASAP after a contest, and the plagiarism test later. We will reduce the cheaters’ ratings later.


Laddus have been given so I guess the plagarism check must have been done by now.

It takes them 2-15 days. Be patient, you will get them soon dear :slight_smile:

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ok, thank you))

I don’t think that there is much scope to detect plagiarism in this case. Dijkstra is one of the BASIC concepts taught in most of the algorithm courses in colleges. If people follow the pseudocode written in books there would be around 10-15 different ways(at max) of implementing it, not more. With 1200+ submissions in this problem it would be really difficult to detect plagiarism. Also, if people copied g4g’s code and got 100, they probably used their own logic to reduce the complexity by not adding all Kc2 edges.


And if codechef punishes people for using dijkstra’s code, then they should also punish people who used Sieve of Eratosthenes and Segmented Sieve for the problem chef and divisor tree lol

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@siddharthp538 please take a look at this:


@qruiger_116 thanks i was searching for that link only

Ohh! Alright. Will keep a note of this. Thanks :slight_smile:

Well if u will reduce the ratings of cheaters afterwards,will u also increase the ratings of others by atleast some value??
Because the cheaters are removed from the ranklist after plagiarism test??

ya that was done even in the old rating system

No, we will not recalculate the ratings after disqualification of cheaters. We ran tests and found that increase in ratings is very small (<= 1 in most cases), and we decided to neglect this, in favor of having consistent, non-changing ratings.

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@admin, It will be really informative for the community if you explain all this in detail in the next blog, not everybody reads the comments.

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