Episode played k times

A podcast app logs every episode play in one session as a list of episode ids, in play order. An analyst wants the episode that was played exactly k times; if several episodes tie, they want the one whose first play happened earliest in the session. Given the log and an integer k (k >= 1), return that episode id, or an empty string when no episode was played exactly k times. For example, with log ["e1","e2","e1","e3","e2","e1"] and k = 2, episode "e2" is the answer.