Mostly only meta knowledge is required. You need to know they exist so you can look them up if you need to reimplement or choose the right library. If you have

Mostly only meta knowledge is required. You need to know they exist so you can look them up if you need to reimplement or choose the right library. If you have to write the code for it inside an existing code base, knowing a specific algorithm by heart vs looking it up won't really make a lot of difference on the time it takes.