Dear CodeCheffers,

At the onset of this new year we are gifting ourselves a new calendar on CodeChef to keep everyone updated on important programming events. If you think we have missed any event please comment on the page to get them added to the calendar.

Have fun,
Tojo Chacko

Hi guys,

We’re finally in the middle of Christmas season! A time for fun and joy and also giving each other lots and lots of presents! Our chef is always excited at this time of the year and cannot wait to reveal his gift for you all.

Are you all ready? *drum roll* With the new year will also come into place our brand new ‘Short Contest Ratings’!

Check out the salient features of our very exciting rating system :-

1. The ratings will take into account COOK01, COOK02, COOK04 and COOK05. COOK03 will not be considered as it was a team based contest.

2. A player will be rated (awarded rating points) in a contest if she has made at least one submission in the contest. If someone doesn’t make even a single submission in the contest then her rating will not change after that contest. (note that it may bring down her rankings).

3. It will be a seed based rating system modeled on the ELO rating. Reference – http://people.ksp.sk/~misof/publications/2009thesis.pdf page – 22.

4. The rating algorithm is a function which takes 2 inputs in the form of Ratings before this contest and Ranks in this contest and gives the final Rating as output. If a contestant participates for the first time in a contest then her previous rating is taken as some default value (say 1000).

5. Mathematical details of the algorithm are described here in brief :-

First for each pair of players (A,B) we calculate the probability of A defeating B and vice versa based on the ELO formula. Then for every player we calculate the sum of probability of defeating other players.

Lets say,
P[B, A(i)] = probability that B defeats A(i).
total[B] = summation of P[B][A(i)] over all A(i).
n = number_of_participants.

The expected rank of a player B in a contest,
E[B] = n – total[B].

We define regular factor for contestant B,
Regular_factor[B] = E[B] – Rank[B].

We have also added a bonus factor so that we can reward extra points to players who have been ranked higher in the contest.
bonus_factor[B] = n/rank[B].

Then for each participating contestant her rating is modified as follows:
New rating[B] = rating[B] + k * regular_factor[B] + m * bonus_factor[B].
Here k and m are constants to give appropriate weight to both the factors.”

Do send in your feedback and let us know what you think of this new rating system for short contests. We hope you are as excited about it as we are!

Best wishes for the new year to you all!

Cheers,
Team CodeChef