hard to write heap sort in functional style with immutable collections. I guess you could write imperative style code.

Well, ah... unless you're applying at Amalgamated SortCo Industries, asking for on-the-spot sorting implementation is pretty high on the list of absurd interview questions.

Anyway I'd think one might use an array and not some other list/collection.

I used clojure once during an interview and bombed, passed again 2 years later at the same company with Python. Would’ve made a big difference in my equity had I just started then!

Yea functional langs just get in the way during interviews. I can write same imperative code i write in java in scala but it just makes it harder( eg: remember to use var instead of val, mutable collections vs default mutable ect) at which point I am just better off practicing for interviews in java.