class Test20 {
    class Solution {
        fun isValid(s: String): Boolean {
            val stack = ArrayDeque(listOf<Char>())
            for (c in s) {
                when(c){
                    ')' ->{
                        if (stack.isEmpty() || stack.last() != '('){
                            return false
                        }else{
                            stack.removeLast()
                        }
                    }
                    '}' ->{
                        if (stack.isEmpty() || stack.last() != '{'){
                            return false
                        }else{
                            stack.removeLast()
                        }
                    }
                    ']' ->{
                        if (stack.isEmpty() || stack.last() != '['){
                            return false
                        }else{
                            stack.removeLast()
                        }
                    }
                    else -> {
                        stack.addLast(c)
                    }
                }
            }
            return stack.isEmpty()
        }
    }

    fun test(): Unit {
        println(Solution().isValid("()"))
        println(Solution().isValid("()[]{}"))
        println(Solution().isValid("(]"))
        println(Solution().isValid("]"))

    }
}