It's easy to understand. For your information, "개수" is the correct spelling.

You explained it in an easy-to-understand way

This seems like a good lecture for people who already know the basics and want to refresh their memory, rather than for beginners like me. I'll think of it as a preview and listen to the lecture. Thank you.

Overall, it's concise but provides good explanations for the necessary parts. It's a great lecture for quickly reviewing concepts that were confusing or unfamiliar. I think it's a good lecture for checking your own development knowledge.