Ask HN: How you keep your algorithm/data structure knowledge sharpen

The question could be a bit of misleading. Just to give you the idea what I am talking. Here is my story: Last year I was looking for a new gig and applied in couple of software companies. I have around 4 years SW development experience mostly web applications based on Python/JS with unix skill.

In the interviews I was really disappointed with myself regarding algorithm/data structure problems. In the interviews the coding test and small projects they asked me to complete was good and eventually I got couple of offers from these employers. But the interviews mostly focused on algorithm/data structure I was massive flop and did not get offer from those companies.

After completing my bachelor when I was looking for my first job, I was asked almost same algorithm/ds problem. At that time I was good but not something overwhelming. Long story cut short, I want to keep my algorithm/ds basics keep sharpen though in day job we dont apply most if the staffs.

Anyone else have the same issue? How you guys do it ? Thanks.