I think codeforces should include a system like rated or unrated before contest otherwise sometimes it effects the rating changes.As far as I know rating changes depends on number of participants when many participants see Problem A is a bit of difficult they quit the contest which reduces the number of participants. So if codeforces can bring a system like you have to ensure yourself whether you want to be rated or unrated just before the contest then It could be more fair who participated in the contest.

Specifically I need some good(not so easy and not so hard) Gym contests for participating individually

Problem Statement:Vanya wants to minimize a tree. He can perform the following operation multiple times: choose a vertex v, and two disjoint (except for v) paths of equal length a0 = v, a1, ..., ak, and b0 = v, b1, ..., bk. Additionally, vertices a1, ..., ak, b1, ..., bk must not have any neighbours in the tree other than adjacent vertices of corresponding paths. After that, one of the paths may be merged into the other, that is, the vertices b1, ..., bk can be effectively erased:

Help Vanya determine if it possible to make the tree into a path via a sequence of described operations, and if the answer is positive, also determine the shortest length of such path.

Problem link:https://codeforces.com/contest/765/problem/E

I want to know the turning point of your coding life. Which was the most strategic practice in your coding life for that you have improved.

Problem link : https://onlinejudge.org/index.php?option=onlinejudge&page=show_problem&problem=3648 This is a Dynamic programming problem.but what should be the approach to solve it. If i do operation only in string x should I think about delete operation because string x is always x<=y.