20. 有效的括号

class Solution {
    public boolean isValid(String s) {

        Deque<Character> deque = new LinkedList<>();
        char ch;
        
        for(int i = 0;i< s.length(); i++){
            ch = s.charAt(i);
            //碰到左括号，就把相应的右括号入栈
            if (ch == '('){
…        }
        //最后判断栈中元素是否匹配
        return deque.isEmpty();
    }
}