Spaced repetition: https://en.wikipedia.org/wiki/Spaced_repetition

If you don't actively review this material you're going to forget it. I created my own study guide for data structures/algorithms that I frequently review to prevent forgetting any concept. Every few days, or at least once a week, I'll take a blank sheet of paper and try to write down everything I possibly know about every fundamental data structure, including pseudocode and real code for operations such as searching/insertion/deletion. When I go through interviews I read my notes and do this active recall exercise at least once a day every day. Unfortunately there's no shortcut and you have to actively think about and code this material in order to remember it (if your day job doesn't involve knowing those things).