Hello. Today I announce three revolutions of AtCoder!

1. AtCoder Library (ACL)

We provide a collection of pre-written codes of various algorithms and data structures. I'll describe details in a separate post.

2. New Color Scheme

Previously, we decided colors by ratings. For example, gold for 3600 and above, silver for 3200 and above, red for 2800 and above, etc. However, it's not clear what the rating values mean, for example, 2800. If we design the rating system relatively well, in the short term the rating 2800 corresponds to a certain level. The skill required to reach 2800 today is probably similar to that of a year ago. However, the structure of the contests may change, the number of users may change, the average level of users may change, etc., and the exact value of ratings is very sensitive to these changes (and it may cause inflation/deflation).

Now I believe ranks are more robust against inflation/deflation and more suitable to decide colors, at least for the top people. It's clear what the $$$k$$$-th rank means — it means you are the $$$k$$$-th strongest person, and that corresponds to how likely you are to get titles in major tournaments, advance to onsite finals, get medals in ICPC/IOI, etc.

Here's the comparison of the new scheme and the old scheme. For now, the cutoff of gold/silver in the two schemes are very similar.

For the same reason, we added rank graphs on your profile page. Once you reach the 100th place, this kind of graph will appear and your journey to reach the first place starts. Good luck.

3. New ARC format

Currently, the bottleneck of holding ARC contests are the last (most difficult) problems. We are in short of high-quality problems of current ARC-F difficulty, and that's why ARCs are not frequent recently. Also, in AGCs and ARCs, we followed the "Quality > Quantity" style in an extreme way.

As a result, we now have really a lot of unused problems of difficulty around 600-700 points. Also, we have a lot of unused good problems, if not great, that deserve to be used in some contests.

I think it's time to start holding more contests using these problems. From October, we'll start holding ARCs with a bit lowered difficulty.

Internally, we are planning to classify problems as follows (in the order of difficulty from top to bottom):

Then the basic guideline of an ARC set will be as follows:

So, the difference of difficulties between ARCs and ABCs will be smaller. The major difference is the style of problems — ARCs will focus on more adhoc, thinking problems, while ABCs will focus on more "educational" part, like learning basic algorithms, typical techniques, etc.

Now we have more than 30 ARC sets on our stock this way. You can expect frequent ARCs in the near future.

Note that we don't change the format/style of AGCs — this change won't affect the "crowned" places.