https://www.4clojure.com/problem/164

4clojure-164.clj

(fn [{:keys [states start accepts transitions]}]
  (->> (conj clojure.lang.PersistentQueue/EMPTY {:prefix [], :pos start})
       (iterate (fn [q]
                  (let [[{:keys [prefix pos]} tail] ((juxt peek pop) q)]
                    (into tail (for [[alpha pos'] (transitions pos)]
                                 {:prefix (conj prefix alpha), :pos pos'})))))
       (take-while peek)
       (map peek)
       (filter (comp accepts :pos))
       (map (comp (partial apply str) :prefix))))