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### sbren_sbeve's blog

By sbren_sbeve, history, 6 weeks ago,

Hello, in this blog I will explain how to set a Div2E/F on Codeforces in $2$ simple steps.

1. Create an easy problem
2. Add the condition $\gcd = k$

1. You don't need to think about the details of the solution. It's enough to solve for all gcds and use either Mobius function or inclusion-exclusion.
2. On the other side, the problem is suitable for Div2E/F because most contestants are too lazy to study basic number theory.
3. This method has been used successfully in a lot of recent rounds! Examples: 1436F - Sum Over Subsets, 1554E - You, 1559E - Mocha and Stars

I hope this blog will be useful for problemsetters!

• +580

By sbren_sbeve, history, 2 months ago,

Is there any rating deflation on AtCoder? Possible proofs:

• These rating graphs: 1 2 3
• Old problems with a rating $x$ (on kenkoooo) seem as hard as new problems with a rating $x-300$

What do you think?

• +109

By sbren_sbeve, history, 3 months ago,

Let's define a coefficient $k$ that calculates the beauty of a problem (higher is better).

### $k = \frac{\text{# of pieces of paper used to solve the problem}}{\text{time spent}}$

Braindead problems (i.e. you know the solution just after you finish reading the problem, then you spend $30$ minutes implementing it) are so annoying.
What do you think?