Auto comment: topic has been updated by Namika (previous revision, new revision, compare).

When you try to solve some problem and fail, it may be because you don't know particular algorithm or data structure. You can see that in the editorial it says that this algorithm is needed to solve it. So you should look up what does that algo/datastruct do and think in which problems it can be useful.

You cannot learn all the concepts. This process never ends.

The general idea is to solve problems. If you're stuck on a problem, read the editorial. Probably, the problem wanted an algorithm that you didn't know. You can study it and solve more problems on the same topic for practice.

For example, when I was solving the problem 230B - Т-простые числа, I found out about Sieve of Eratosthenes in the editorial. Then I studied number theory (Sieve, GCD and Modular Arithmetic).

Watch this video

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Auto comment: topic has been updated by Namika (previous revision, new revision, compare).

Here You will find some resources... https://mirror.codeforces.com/blog/entry/122788