#include using namespace std; class Solution { public: vector result; void helper(int open, int close, int n, string curr) { if (curr.length() == n * 2) result.push_back(curr); if (open < n) helper(open + 1, close, n, curr + '('); if (close < open) helper(open, close + 1, n, curr + ')'); } vector generateParenthesis(int n) { helper(0, 0, n, ""); return result; } }; int main() {}