Most leetcoders simply memorize one or two solutions instead of studying algorithms holistically. I suspect that many would spend time understanding that generating gray code can be mapped to mixed-radix number system (nor should us anyway, albeit it's really really cool). Leetcode does not require understanding of advanced data structures either. Instead, it's full of clever tricks and specific solutions with which entry-level ACM participants are well versed.

I think it's harder to memorize hundreds of solutions than it is to understand a few tens of algorithms and their use cases.

Like with math, it's easier to learn to solve problems than to learn by heart hundreds of potential problems the teacher might give you on an exam.