[8xde0wcNwpslOw]

>checking if a map or set contain a key requires lots of code

Well, we all have our own standards, but...

  std::set<int> numbers = ...;
  if (numbers.count(5)) {} // we have a 5

[JanisL]

What's the complexity of that operation?

[plorkyeran]

It is exactly the same operation as `contains()` for set/map. There's only a difference between `count()` and `contains()` for multiset/multimap.