题目链接https://leetcode.cn/problems/IDBivT/description/

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

class Solution {public List<String> generateParenthesis(int n) {List<String> res = new ArrayList<>();String s = "";dfs(0,0,n,res,s);return res;}public void dfs(int left,int right,int n,List<String> res,String s){//left记录左括号数，right记录右括号数。if(right > left || left > n){//失败的情况return;}if(right == n && left == n){//左右括号数目都是n时，添加到resres.add(s);return;}dfs(left+1,right,n,res,s + "(" );dfs(left,right+1,n,res,s + ")" );}
}