Balancing Brackets – Rich 4Clojure Problem 177 – See: https://github.com/PEZ/rich4clojure

rich4clojure_medium_problem_177.clj

(ns rich4clojure.medium.problem-177
  (:require [hyperfiddle.rcf :refer [tests]]))

;; = Balancing Brackets =
;; By 4Clojure user: daowen
;; Difficulty: Medium
;; Tags: [parsing]
;; 
;; When parsing a snippet of code it's often a good idea
;; to do a sanity check to see if all the brackets match
;; up. Write a function that takes in a string and returns
;; truthy if all square [] round () and curly {} brackets
;; are properly paired and legally nested, or returns
;; falsey otherwise.

(def __ :tests-will-fail)

(comment
  
  )

(tests
  "This string has no brackets." :=
  "class Test {
      public static void main(String[] args) {
        System.out.println(\"Hello world.\");
      }
    }" :=
  (__ "(start, end]") :=
  (__ "())") :=
  (__ "[ { ] } ") :=
  "([]([(()){()}(()(()))(([[]]({}()))())]((((()()))))))" :=
  (__ "([]([(()){()}(()(()))(([[]]({}([)))())]((((()()))))))") :=
  (__ "[") :=)

;; To participate, fork:
;; https://github.com/PEZ/rich4clojure

;; Post your solution below, please!

(defn brackets [[h & t :as stack] br]
  (case br
    (\( \{ \[) (cons br stack)
    (\) \} \]) (case (str h br) ("()" "[]" "{}") t (reduced [h]))
    stack))

(defn balanced? [s]
  (->> s (reduce brackets '()) empty?))