you do convert the array into a string, check what delete_at returns. please do not raise issues so lightly in the future

./lib/solution.rb:15:in block in valid_braces': undefined method delete_at' for "({":String
Did you mean? delete
delete! (NoMethodError)

How can variable be string if I declare it in my code as Array and never convert it to String?

Is it me or it doesn't work in Clojure? There's a "java.lang.NullPointerException: null" in some tests here but the same code in REPL works just fine