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 { public: vector<string> generateParenthesis(int n) { vector<string> ans; backtrack(ans,"",0,0,n); return ans; } void backtrack(vector<string>& ans,string current,int open,int close,int n){ if(current.size()==2*n) { ans.push_back(current); return; } if(open<n) { backtrack(ans,current+'(',open+1,close,n); } if(close<open) { backtrack(ans,current+')',open,close+1,n); } } };