Generate Parentheses

class Solution {public:    vector<string> generateParenthesis(int n)     {        vector<string> result;        if(n > 0)            dfs(result,"",n,n);        return result;    }        void dfs(vector<string> &result,string cur,int left,int right)    {        if(left==0 && right ==0)            result.push_back(cur);                if(left > 0)            dfs(result,cur+"(",left-1,right);        if(left<right && right>0)            dfs(result,cur+")",left,right-1);    }};

参考了 http://www.shangxueba.com/jingyan/1837405.html