There seems no.

Practice problems have nothing to do with scores and rankings in the official competition, so I think you can discuss problems anytime you want. I have been seeing several discussions on practice problems in some Chinese cp forums.

C, D and F are interesting, E is quite standard, and B is too hard for me.

Why the time limit of G is 3s... My FFT solution passes. It does not seem to be the intended solution.

My idea during the contest is to use a segment tree to simulate augmentations in max cost flow. It is simple but requires tedious coding and effort to fit the memory limit. I thought this was the intended solution, but it seems that the intended solution is a much cleaner one, so I take my previous word back.

G is unsuitable for a codeforces contest.

I think A is the hardest among first 5 problems in div 1.

You can find it in Library Checker. lol

Implementation contest :(

Div1F doesn't seem so hard(If it's correct that after contracting three-edge-connected components as single nodes, the graph would be a cactus.), but it requires tooooooooooooo much implementation.

It also needs some effort to code Div1E.

Though I don't know how to prove or disprove this, the conclusion recalls me 102055C - GCD Land. My solution requires finding $$$p \in (\sqrt{n}, n)$$$ and $$$k \geq 2$$$ such that $$$p\ \text{is prime}, (kp+1)\ \text{is prime}$$$ and $$$(k+1)p+1 \lt n$$$. Such $$$p$$$ and $$$k$$$ exist for $$$35 \leq n \leq 10^5$$$, but I don't know their existence for larger $$$n$$$ either. Maybe this would be easier to prove.

Platinum problem 1 resembles JOI Final 2014 Problem 5 :o

What the hell, just mistake cell for grid point in E :(

Is it div.3?