Balanced brackets: Difference between revisions

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Inline

@@ Line 1,577: / Line 1,577: @@
 	  (recur coll (pop stack))))
       (zero? (count stack)))))</lang>
+There are other ways to express the <code>balanced?</code> function.
+* We can use <code>reduce</code> to consume the sequence:
+:<lang Clojure>(defn balanced? [s]
+  (empty?
+    (reduce
+      (fn [stack first]
+        (case first
+          \[ (conj stack \[)
+          \] (if (seq stack)
+               (pop stack)
+               (reduced [:UNDERFLOW]))))
+      '()
+      s)))</lang>
+* Only <code>[</code>s are put on the stack. We can just count the unmatched ones.
+:<lang Clojure>(defn balanced? [s]
+  (let [opens-closes (->> s
+                          (map {\[ 1, \] -1})
+                          (reductions + 0))]
+    (and (not-any? neg? opens-closes) (zero? (last opens-closes))))) </lang>
 Output:
@@ Line 1,582: / Line 1,604: @@
 <pre>user> (->> (range 10)
      (map gen-brackets ,)
-     (map (juxt identity balanced?) ,) vec)
+     (map (juxt identity balanced?) ,)
+     vec)
 [["" true]
  ["[]" true]