第一题 计算圆括号的配对数、落单左括号数、落单右括号数 public static void main(String[] args) { Scanner sc = new Scanner(System.in); String str = sc.next(); Stack<Character> stack = new Stack<>(); //遇到左括号进入,遇到右括号弹出 int pairnum = 0,leftnum = 0,rightnum = 0; for(int i = 0;i<str.length();i+...