I realize that the interviewee was in time pressure, but really should've made smaller helper functions - probably would have helped ease the stress a lot. Poss

I realize that the interviewee was in time pressure, but really should've made smaller helper functions - probably would have helped ease the stress a lot. Possibly also unfamiliar with Clojure/functional programming as someone mentioned, given that his "happy" function uses loop unnecessarily. Here's my solution. (defn int-to-digits [n] (map #(Character/getNumericValue %) (str n))) (I had to Google Character/getNumericValue - doubt anyone expects you to memorize that). (defn next-happy [n] (reduce + (map #(* % %) (int-to-digits n)))) (defn happy? [n] (loop [n n seen #{}] (if (contains? seen n) (== n 1) (recur (next-happy n) (conj seen n))))) A lot simpler to reason about, even if the initial implementation did have bugs.