Where can I get interesting puzzles to consolidate the theory of algorithms?

Question

Programming

Tell me where you can find interesting programming problems with ready-made solutions, the purpose of which is to show how to correctly use the knowledge of algorithms.
The tasks are interesting for those that are suitable for a beginner in programming (he will be able to understand their ready-made solution), well, it is desirable that they are not dry (interesting examples),
I think I will formulate the question more precisely later.

Answer 1

Perhaps here you will find something interesting for yourself: e-maxx.ru

Answer 2

acm.timus.ru

Answer 3

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