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.