solution_177 http://www.4clojure.com/problem/177

solution_177.clj

; solution to http://www.4clojure.com/problem/177

(defn balanced?                                                                      
  [x]                                                                                
  (let [tokens (vec (clojure.string/replace x #"[^\(\)\[\]\{\}]" ""))                
        brackets { \{ \} \( \) \[ \]}                                                
        starting-bracket? (fn [x] (brackets x))                                      
        matching-bracket? (fn [a b] (= (brackets a) b))]                             
    (loop [stack '()                                                                 
           [curr & more] tokens]                                                     
      (if (nil? curr)                                                                
        (empty? stack)                                                               
        (recur (if (or (starting-bracket? curr)                                      
                       (not (matching-bracket? (first stack) curr)))                 
                 (conj stack curr)                                                   
                 (rest stack))                                                       
               more)))))                                                             

; tests

(balanced? "())")                                                          
false                                                                                     

(balanced? "([]([(()){()}(()(()))(([[]]({}()))())]((((()()))))))")         
true                                                                                      

(balanced? "([]([(()){()}(()(()))(([[]]({}([)))())]((((()()))))))")        
false                                                                                     

(balanced? "[")                                                            
false