LeetCode刷题之路：22. 括号生成

数字 n 代表生成括号的对数，请你设计一个函数，用于能够生成所有可能的并且 有效的 括号组合。

示例 1：

输入：n = 3
输出：["((()))","(()())","(())()","()(())","()()()"]
示例 2：

输入：n = 1
输出：["()"]

提示：

1 <= n <= 8

class Solution:
    def generateParenthesis(self, n: int) -> List[str]:
        res = [["None"], ["()"]]
        for i in range(2, n+1):
            tmp = []
            for j in range(i):
                q = i - 1 - j
                list1 = res[j]
                list2 = res[q]
                for a in list1:
                    for b in list2:
                        if a == "None":
                            a = ""
                        if b == "None":
                            b = ""
                        tmp.append("(" + a + ")" + b)
            res.append(tmp)
        return res[n]