Fix StackOverflow error on large inputs

Use non-lazy collections.

src/com/owoga/tightly_packed_trie.clj

@@ -233,7 +233,7 @@
             current-depth (count (first current-node))]
         (cond
           (empty? nodes)
-          (let [child-index (first child-indexes)
+          (let [child-index (last child-indexes)
                 child-index-baos (ByteArrayOutputStream.)
                 _ (->> child-index
                        (run!
@@ -267,9 +267,9 @@
           ;; Gone up from depth to a parent.
           ;; Process index of children.
           (> previous-depth current-depth)
-          (do (let [[k v] (first nodes)
+          (let [[k v] (first nodes)
                 value (value-encode-fn v)
-                    child-index (first child-indexes)
+                child-index (last child-indexes)
                 child-index-baos (ByteArrayOutputStream.)
                 _ (->> child-index
                        (run!
@@ -283,7 +283,7 @@
                             (- current-offset offset))))))
                 child-index-byte-array (.toByteArray child-index-baos)
                 size-of-child-index (encoding/encode (count child-index-byte-array))
-                    current-index (second child-indexes)]
+                current-index (last (pop child-indexes))]
             (.write baos value)
             (.write baos size-of-child-index)
             (.write baos child-index-byte-array)
@@ -293,20 +293,19 @@
                       (count size-of-child-index)
                       (count child-index-byte-array))
                    current-depth
-                       (cons (conj current-index
+                   (conj (pop (pop child-indexes))
+                         (conj current-index
                                [(last k)
-                                    current-offset])
-                             (drop 2 child-indexes)))))
-
+                                current-offset]))))
           ;; Down or even in depth to children
           ;; Start keeping track of new children index
           :else
-          (do (let [[k v] (first nodes)
+          (let [[k v] (first nodes)
                 value (value-encode-fn v)
                 size-of-child-index (encoding/encode 0)
-                    child-indexes (concat (repeat (- current-depth previous-depth) [])
-                                          child-indexes)
-                    current-child-index (first child-indexes)]
+                child-indexes (into child-indexes
+                                    (vec (repeat (- current-depth previous-depth) [])))
+                current-child-index (last child-indexes)]
             (.write baos value)
             (.write baos size-of-child-index)
             (recur (rest nodes)
@@ -314,10 +313,10 @@
                       (count value)
                       (count size-of-child-index))
                    current-depth
-                       (cons (conj current-child-index
+                   (conj (pop child-indexes)
+                         (conj current-child-index
                                [(last k)
-                                    current-offset])
-                             (rest child-indexes))))))))))
+                                current-offset])))))))))
 
 ;; TODO: Shared "save" interface for Trie?
 (defn save-tightly-packed-trie-to-file