[LeetCode] 1190. 反转每对括号间的子串

考察栈的使用，需要注意边界情况。不难，想全TestCase很容易1A通过

class Solution {
    public String reverseParentheses(String s) {
        Stack<Character> stack = new Stack<>();
        if (s.length()==0) return "";

        for (int i = 0;i<s.length();i++) {
            if (s.charAt(i) == ')') {
                reverse(stack);
            } else {
                stack.push(s.charAt(i));
            }
        }

        String ans = "";
        while (!stack.empty()) {
            Character ch = stack.pop();
            if (ch!='(') {
                ans+=ch;
            }
        }

        return new StringBuilder(ans).reverse().toString();
    }

    private void reverse(Stack<Character> stack) {
        List<Character> tmp = new ArrayList<>();

        while (true) {
            Character ch = stack.pop();
            if (ch == '(') {
                int i=0;
                while (i<tmp.size()) {
                    stack.push(tmp.get(i++));
                }
                break;
            }
            tmp.add(ch);
        }
    }
}