Interview question - merge two sorted linked lists

merge-sorted-lists.clj

;; merge two sorted linked lists
;; h1 => 2 => 3 => 5
;; h2 => 4 => 4 => 6 => 7
;; h => 2 => 3 => 4 => 4 => 5 => 6 => 7

(defn splitter [lst1 lst2]
  (cond (empty? lst1) [lst2 nil nil]
        (empty? lst2) [lst1 nil nil]
        :else (let [[l1 l2] (if (< (first lst1) (first lst2)) [lst1 lst2] [lst2 lst1])]
                (concat (split-with #(<= % (first l2)) l1) [l2]))))

(defn merge-lists [lst1 lst2]
  (let [res (atom [])]
      (loop [l1 lst1 l2 lst2]
        (let [[final next1 next2] (splitter l1 l2)]
          (swap! res conj (vec final))
          (if (or next1 next2)
            (recur next1 next2))))
      (flatten @res)))

(merge-lists [2 3 5] [4 4 6 7])