Zuckerberg was able to build Facebook because he got a good education and understood graph theory enough to apply it to social networks.

In the past, the only people who really understood concepts like graphs were people who endured rigorous four-year computer science curriculums. And only top students at elite schools would learn this. The average CS graduate has a very poor understanding of fundamental data structures and algorithms.

But with Leetcode, anyone can solve 5-10 graph problems and obtain the same knowledge. It's extremely efficient. In a couple of days, you can learn what used to take years.