bigger.clj

(defn decreasing-from-last [v]
  (loop [start (dec (.length v))]
    (let
        [prev-start (dec start)]
        (cond
          (< prev-start 0) 0
          (neg? (compare (get v prev-start) (get v start))) start
          :else (recur (dec start))))))

(defn next-permutation [v]
  (let [split-point (decreasing-from-last v)]
    (cond
      (= 0 split-point) v
      :else v)))

(defn solve [input]
  (let [result (next-permutation (vec input))]
    (cond
      (= result input) "no answer"
      :else (clojure.string/join result))))