djm03178's blog

Div. 2 C's are NOT getting easier
By djm03178, 8 hours ago, In English

Recently, after like every Div. 2 contest I see some blogs/comments saying that ~2C problems are getting easier. What's the evidence? They say these problems have many solves.

No, I think it's the opposite.

Definite number of solves is not a good measure for evaluating the difficulty. A not too precise, but statistically more reliable way to evaluate the difficulty of a 2C problem would be calculating (# of official solves on C) / (# of official solves on A), assuming that most people have always been able to solve 2A.

Let's calculate them for recent 10 Div. 2-only contests' (not counting Educational rounds) C problems:

In average it's around ~33.6%.

So, was it harder a year ago? Let's check 10 contests from exactly 1 year ago:

In average it's around ~38.4%.

As you can see, this proportion in recent rounds has actually decreased compared to 1 year ago. Although it's not drastic, we can't really seem to be able to say that 2C's are "getting easier". Furthermore, with the amount of cheats nowadays, after we remove such counts, we can almost surely say that the problems are actually getting harder.

So, is this 'traditionally' the intended difficulty of 2C? Well, let's take a look at the contests 5 years ago:

It looks more significantly different. In these contests, the average is around ~46.7%.

As I wrote in a previous blog, I think recent rounds of lower divisions are generally too hard, and part of the reason I think is that people are scared of getting too large absolute number of solves. Having 40 solves on 2F nowadays isn't same as having 40 solves on 2F 5 years ago. Nobody would argue that a 2F was too easy if it had 10 solves 5 years ago, but these days people will complain 40 solves on 2F is way too easy, even though the number of participants has increased like 4 times. Similarly, having 8k solves on 2C nowadays isn't same as having 8k solves on 2C 5 years ago. It's like having 2k solves back then, which nobody would've thought to be too much.

Also, I want to believe that as time goes on, the average skill level of participants also increases, so if two problems have similar value of this proportion, then the one made recently is more likely to be harder. We are not getting easier problems than before.

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8 hours ago, # |
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The chat gpt compressed the text for me and said "skill issue".

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7 hours ago, # |
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It's not div2C getting harder, it's people getting weaker

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7 hours ago, # |
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Wouldn't average problem rating be a better metric of C difficulty instead of solve percentage? Solve percentage can also decrease if there is a disproportionately larger number of greys/greens who aren't at C level yet. Unless there's something wrong in this thinking? I'm not sure how exactly problem ratings are calculated, but surely they take into account the ratings of participants who solved them?

I still think it's very hard to compare because problem ratings from 5 years ago will probably shift if they were re-calculated today.

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    7 hours ago, # ^ |
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    I agree, but it's hard to collect the full information of contestents and even if we use the API it doesn't provide us the true rating, so it's hard to predict the real rating distribution of the participants. I wanted a simpler way to briefly show the overall tendency. It didn't need to be very precise.

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      7 hours ago, # ^ |
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      Yeah that makes sense, thanks for the effort!

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      3 hours ago, # ^ |
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      You don't need information about contestants to get problem rating. This is a number just near the problem tags.

      By the way, it can be collected manually for just same 30 contests that were mentioned in your blog. Will be very interesting to see the result. Also think that problem rating can be collected automatically.

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    6 hours ago, # ^ |
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    Problem rating is an unideal metric because often, an 1800 from years ago won't be the same level as an 1800 now. I think this ratio of solved C / solved A makes more sense.

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6 hours ago, # |
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I agree that the C`s are hard

But The submission percentage difference between previous year and current years may be because of the following reasons: * The number of newer participants increased

  • most participants are less rated (newbies and pupils) like me , who effect the total count to submitted count rate.
  • earlier(previous years) the number of participants at a good level , are more and today they remain there (those who solve C today).

some sources : that say that new participants(with lower rating) has increased over the years

https://codeforces.com/blog/entry/126802

https://www.linkedin.com/posts/priyansh-agarwal_i-compared-the-stats-of-indian-coders-on-activity-7218249783780524032-O9n1?utm_source=share&utm_medium=member_desktop

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    6 hours ago, # ^ |
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    Thanks for the articles. It makes sense. Maybe it explains a bit of bias in my blog.

    I wonder how many greys actually participate in Div. 2s, since I've seen many people trying to avoid Div. 2 because they could solve only around 1-2 problems and are likely to lose rating. As we can see in recent contests, Div. 3/4 rounds usually have around 10k more participants due to this.

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6 hours ago, # |
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There're already more Div.3s and Div.4s, you can't hope that Div.2s will be as easy as before. Moreover, we can't always step around and around. Harder problems are good for academic progress.

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    6 hours ago, # ^ |
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    I'm not saying we should lower the difficulty of 2C's (the other blog is more about the hardest problems). Just wanted to say that the actual tendency of 2C's is not how many people judge just by the number of solves.

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      6 hours ago, # ^ |
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      If the tone is a bit inappropriate, it's my problem, sorry. My actual meaning is only to state objective facts, 'you' does not really refer to you.

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        6 hours ago, # ^ |
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        No problem, I appreciate your opinion.

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6 hours ago, # |
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I won't compare it to 1 year ago but compare it to the contests just a month ago to see the number of solves. Also, comparing it with A might be a wrong way to estimate the difficulty because the difficulty of As and Bs have dropped too!

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57 minutes ago, # |
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You have to admit because of the quantity of alts and cheaters nowadays, the true solve rate of 2C might be much lower than your estimation.

I think 2C is harder than before.

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    32 minutes ago, # ^ |
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    Do you have any concrete proofs for this kind of claims? Or are they nothing but your gut feelings amplifying the truth for your own petty satisfaction in mind?

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18 minutes ago, # |
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Is this his end of cp?

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