Clojure flat sequence into tree

Question

I have the following vector, [-1 1 2 -1 3 0 -1 2 -1 4 0 3 0 0]

which represents the tree [[1 2 [3] [2 [4] 3]]]

where -1 begins a new branch and 0 ends it. How can I convert the original vector into a usable tree-like clojure structure (nested vector, nested map)? I think clojure.zip/zipper might do it but I'm not sure how to build those function args.

Answer 1

Zippers are a good tool for this: 

(require '[clojure.zip :as zip])

(def in [-1 1 2 -1 3 0 -1 2 -1 4 0 3 0 0])
(def out [[1 2 [3] [2 [4] 3]]])

(defn deepen [steps]
  (->> steps
       (reduce (fn [loc step]
                 (case step
                   -1 (-> loc
                          (zip/append-child [])
                          (zip/down)
                          (zip/rightmost))
                   0 (zip/up loc)
                   (zip/append-child loc step)))
         (zip/vector-zip []))
       (zip/root)))

(assert (= (deepen in) out))

Answer 2

Somehow this feels like cheating:

[(read-string
  (clojure.string/join " "
                       (replace {-1 "[" 0 "]"}
                                [-1 1 2 -1 3 0 -1 2 -1 4 0 3 0 0])))]