"Drawbacks" was the wrong word to use here, "potential problems" is what I meant - collisions. Normally a follow up question: how do you solve those. But drawbacks too: memory usage - us developers are pretty used to having astronomical amounts of computational resources at our disposals but more often than not, people don't work on workstations with 246gb of ram.
I think the better word is tradeoff since there are no perfect data structures for each job. The hasmap has the advantage of O(1) access time but the drawback of memory usage, an unsorted nature and the depends on a good hashing function to minimize collisions. A vector is also O(1), but it has an upfront memory cost that cannot be avoided. A map has a O(Log(n)) access cost, but has less memory usage, is sorted by nature and the comparison function is easier to implement.
Three similar data structures, but each with its own tradeoffs.
Good point about collisions. When I wrote the original post, I didn't think about that. As a primarily CRUD developer, I never think about collisions. The default general purpose hash map in all of my languages is fine. That said: It does matter, and it is a reasonable topic for an interview!
