If you don't know in your heart the time complexity of a small number of basic, fundamental algorithms and data structures, this is at least a yellow flag.

When I was interviewing, I never required anyone to know any specific algorithm, but if someone didn't know, say, the existence of some container where insertion and retrieval are O(1), then this puts a limit on how good they could be.

On the other hand, I remember one candidate who got to the point where he needed an O(1) container and said, "I know there exist containers where you can do inserts and retrieval in constant time, but I forget what they are called," and I said, "No problem, it's called [XXX]. Now, if you had such a container how could you solve this problem?", and I gave him top marks and he got hired. I didn't care he didn't remember the specific name, because you can just look that up - he knew the sort of thing he needed and that's what counted.