If you are triggered by this clickbaity blog title, you are probably interested in improving your Codeforces skills. Now, I will share my point of view on the differences between Codeforces and ICPC contests, and how you can, in my humble opinion, maximize your Codeforces rating gain.
I mostly consider that all conceivable competitive programming problems need three aspects of skill:
Observation — the ability to understand the problem and come up with non-trivial properties.
Technique — the ability to apply a well-known algorithm or data structure to the problem.
Implementation — the ability to code fast and debug fast.
Collaterally, I refer to these three skills as Russian-ness, Chinese-ness and American-ness, respectively, for reasons you will soon see below.
Observation (Russian-ness)
Observation means that you stare at some problem for a sufficient amount of time and you are able to reduce it to some easier problem. One good problem that I think is interesting is this 1889D. Despite being rated 3000, the problem is solvable in 30 lines of trivial code. Of course, there are also bad problems, such as the infamous 1916D and 1916H1, but the gist is that the problem needs good mathematical thinking and nothing else.
I consider this aspect of difficulty to be *Russian*because this type of problem happens more often in Russian ICPC-style contests, specifically OpenCup and ICPC camp, etc. They are also single-handedly the most popular problem style on Codeforces and AtCoder.
Now the interesting part about it is that since the skill level correlates to math skill and nothing else, you can literally do IMO problems instead of Codeforces problems. For instance, if you take this problem list from IMO2022 and look at the combinatorics problems in it, you will see that they translate nicely to Codeforces Div. 1 problems. There is a saying that math majors have an advantage over CS majors in Codeforces, and I think it is justified to some extent.
Technique (Chinese-ness)
Technique is the more common thing you will learn at any competitive programming course, such as binary exponentiation, segment tree, etc. Obviously, it is not fully possible to distinguish techniques from observation, but I draw the line as to whether it is possible to produce a reference code for the thing in question. So dynamic programming and greedy are more Russian, and Fenwick tree and segment tree are more Chinese.
Now I call these problems Chinese because Chinese OI and ICPC have a tendency to produce problems that are solvable only by advanced data structures that are only possible if you have a reference code. For instance, 104857C is solvable only with a palindrome tree, and 104857A is solvable only if you took some graduate course.
I guess this is the most learn-able part of all, and what most learners of competitive programming will engage with. Now we get the intuition why it is so hard to improve at Codeforces: you are trying so hard to become Chinese instead of becoming Russian!
Implementation (American-ness)
Implementation mostly refers to problems that take a lot of time to implement, such as geometry problems that are very popular in US contests, such as 104757C from the recent ECNA. I mostly consider that there are two difficulties in implementation. One is that the code is just long but is not particularly tricky, such as the famous Rubik's cube; the other is that the code consists of many cases and is hard to get right, such as 104869I.
Now I call these problems American because geo problems usually require a code reference and are pretty popular in US regionals.
Summary
Now, what does Codeforces stand in all of this? I will make one bold claim here: for Codeforces now, you only need Leetcode medium + high school math contest to get to blue. I will try to argue for it in these two claims.
Claim 1: You only need to finish Div. 2 A, B, C in one hour to get to blue.
This is trivially true by looking at past contests.
Claim 2: Div. 2 A, B, and C require nothing but basic programming skills and good math skills.
This is more debatable, but I think none of them require any noticeable techniques other that mathematical analysis. Therefore, being good at middle and high school math contests suffices.
Now we can answer the golden question of all time.
- How do I improve at Codeforces (for now)?
A lot of people in Codeforces Catalog will just say that you should do more problems. That is obviously true, but it reminds me of this interesting joke:
Why learn swimming? Just jump into the river. It works for everyone who lives after that!
I think, ultimately, this line of thought just loses people out of competitive programming for thinking that they are not clever enough. I hope this blog convinces you that Codeforces for people below Div. 1 has nothing to do with programming but everything to do with math. Therefore, to study for Codeforces you should not study programming but instead study for math contests!
- Why haven't I become better at Codeforces after reading through cp-algorithms?
Because Codeforces has nothing to do with competitive programming algorithms for people below Div. 1. Just study math problems instead!
- Should Codeforces be so 'Russian'?
Now, obviously, it's not for my humble mortal mind to ever contemplate the masterful design of Russian grandmasters such as 74TrAkToR. But I think, in general, when a problem that has a higher Chinese difficulty is proposed, the response is
This problem seems too standard (translate: is not Russian enough). It would be a good one for an educational round, but not a regular one.
As for American-ness, well...
When was the last time you saw a geo problem in a Codeforces contest?
Jokes aside, it is beyond me to say what should be more important in competitive programming contests, but I do think the community should reflect on this interesting difference between Codeforces and ICPC.
Alright, now, before I got nuked by the three largest countries of the world, canceled by the greatest grandmasters on Codeforces, and downvoted to oblivion, I think it is high time that I bail out. I will end with this sentence.
May the Russian-ness be with you.
