If I decide to learn an algorithm or a data structure with which I am not familiar yet, and decide to read some blog or an article about that algorithm or data structure or watch some video tutorials, and solve some problems (like 4-5 problems) (which are usually provided in the blog) related to it, can I now conclude that I have learned that algorithm or data structure? Can I now expect myself to solve any problem related to it, if it comes in any contest?
No you cant say that you have learned the algorithm untill you solve a problem without knowing that it belongs to that concept like if in a contest or a random practice session if you could come up with that approach more than once you can consider it learnt.