solimm4sks's blog

Problem Difficulty
By solimm4sks, history, 5 years ago, In English

I have been noticing this for quite some time now, but I always just glossed over. Just wanted to share, so I'll make a short post about it.

I have seen quite a few problems that seem to have a very high difficulty(sometimes same as Div2C / Div2D) even though they are Div2A. For example: https://codeforces.com/problemset/problem/518/A

This is a pretty easy problem and I just can't fathom why it would be the same difficulty (1600) as for example: https://codeforces.com/problemset/problem/570/C or even a Div2D!!: https://codeforces.com/problemset/problem/735/D

I have seen this happen more often for older contests, but I may be mistaken. I figured, maybe I could find a reasoning if I read more about how problem difficulties are calculated: https://codeforces.com/blog/entry/62865 but from this it seems like that you have to be an expert to have a >= 50% chance at solving the mentioned Div2A problem. What??

It doesn't really bother me all that much, I just wanted to share and am wondering if anyone stumbled upon such "high difficulty" problems and if you have any idea why their difficulty is so high.

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5 years ago, # |
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For the particular problem you mention, the reason of its rating being high is because only 795/3044 official participants solved it in contest, and although that was most probably because of an edge case which people missed and led to a lot of hacks/system test fails, for Codeforces Difficulty Evaluation, it's as good as 795/3044 people solving it in contest, which is comparable to a Div2C difficulty generally.

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    5 years ago, # ^ |
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    Thanks for the comment! :D That makes sense. It kinda sucks that easy problems can be evaluated with a high difficulty because of edge cases but I guess it can't be helped. There are a lot of problems on the site so it only makes sense that a few will have their difficulty skewed.

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5 years ago, # |
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I think there are two main reason: Firstly it depends on the porpotion of the participants who got AC on the problem and secondly, there are just a whole lot of people who are more skillful than you. For example, you found that the Div2D problem is hard but actually, Goldbach's conjecture instantly kill it

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5 years ago, # |
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I would say this is harder than average div2-a problem and hence the difficulty 1600. It's hard for organizers to always estimate the difficulty correctly. I would say this one was more like div2-b.

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