Uses reduce to check if brackets are balanced

is-balanced.clj

(def brackets {\{ \}
               \[ \]
               \( \)})


(defn checker [stack char]
  (if (some #{char} (keys brackets)) ;; Is the character an opening bracket?
    (conj stack char)
    (let [closing-char (get brackets (last stack))]
      (if (= closing-char char)
        (pop stack) ;; Remove the last character in the stack
        (reduced (conj stack char)))))) ;; Stop. It's unbalanced. Make sure stack is not empty to induce `false` in parent function.


(defn is-balanced [s]
  (let [all-brackets (set (into (keys brackets) (vals brackets)))
        chars (filter all-brackets s)]
    (empty? (reduce checker [] chars))))


(is-balanced "[hello (world)]")
;; => true

(is-balanced "[hello (world]")
;; => false

(is-balanced "[hello (world)]))))")
;; => false