What is the performance of `count` on a Clojure set?

Question

So, I read that the `count` operation is O(1) for a Clojure vectors, lists and maps. ``` (count [1 2 3]) ;=> 3 ``` But is it also O(1) for a Clojure set? I imagine it probably is, but I'm not really sure how to find out. I had a quick read of http://clojure.org/data_structures#Data%20Structures-Sets, but couldn't see the info there.

Accepted Answer

It is `O(1)`

You can verify this by observing that `clojure.lang.PersistentSet` maintains a `_count` field in the Java source code:

https://github.com/clojure/clojure/blob/master/src/jvm/clojure/lang/PersistentList.java

What is the performance of `count` on a Clojure set?

Solution

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