i was able to successfully solve one question(ATTIC) from last night’s Cook35. but strangely once the rankings were upgraded, i fell by almost a 1000 ranks and my rating decreased as well. how is that possible? if i successfully submit an answer either my rating should be unchanged or increase right? an other user also solved just this question, that too in 8 times the execution time of my solution but his rating points increased! what is happening here?!?!?!
The rating is not dependent on execution time but time required to complete a question plus 20 min for each incorrect submission.
Your rating reduced because initially you had 1000 points(by default) and the code chef’s rating algorithm rates you lower than this so it reduced. Same thing happened with me for my 1st 2 cook-offs even though i solved 1 question in each.
Modified Elo rating is used on CodeChef (and other competition sites - CodeForces, TopCoder).
The idea is, that your rating depends on your performance in contest comparing to other competitors. Very simple idea of how it works is, that all competitors are sorted by actual rating - this is expected result in competition. And in final result you performed better than system expected, your rating increase, if you perform worse than expected your rating decrease.
There are exact formulas how it is calculated, but I think it’s no so important.
Note: Not only number of solved problems is important, in short contest the solving time is important to. As you can see, competitors 63-309 (June Cook-Off 2013 rank) all solved 2 problems, but the final result is important as I described before. Similar idea holds for long contest with the difference, that time is not important…
More about ratings can be found out here : http://blog.codechef.com/2010/12/27/a-surprise-in-store-this-new-year.
This blog explains how the ratings for CodeChef challenges is computed.
Hope it clears all your doubts about rating points.
Anyways @betlista has explained it well using the practical example.
ohh really? causei forgot that there was a contests and i logged in at 11:45 and there were only 15 min left for the contest to end. so i barely submitted one in time. what do u mean plus 20min for each incorrect answer?
look at place 397 here - http://www.codechef.com/rankings/COOK35, he got accepted after 18 minutes, but because of first incorrect submittion final time is 38 minutes… Without the submission he would be 80 places better.
ohhh niceeee. thanks dude
@betlista I guess you need to edit your comment, it’s not 394, infact it is 397. So could you please edit your comment to avoid confusion. Anyways nice example to show the effect of wrong submission on the ratings.
@vian: thanks for the correction, fixed