二刷Leetcode-Days09

栈与队列：

    /**
     * 20. 有效的括号
     * @param s
     * @return
     */
    public boolean isValid(String s) {
        Deque<Character> deque = new LinkedList<>();
        for (int i = 0; i < s.length(); i++) {
            char ch = s.charAt(i);
            //碰到左括号，就把相应的右括号入栈
            if (ch == '(') {
                deque.push(')');
            }else if (ch == '{') {
                deque.push('}');
            }else if (ch == '[') {
                deque.push(']');
            } else if (deque.isEmpty() || deque.peek() != ch) {
                return false;
            }else {
                //如果是右括号判断是否和栈顶元素匹配
                deque.pop();
            }
        }
        //最后判断栈中元素是否匹配
        return deque.isEmpty();
    }