Generate Parentheses

class Solution {public:    vector<string>res;    vector<string> generateParenthesis(int n) {        generate(0,2*n,0,0,"");        return res;    }    void generate(int dep,int maxdep,int leftnum,int lefttotal,string s)    {        if(lefttotal*2>maxdep)            return ;               if(dep==maxdep)        {            res.push_back(s);            return;        }        dep++;        for(int i=0;i<2;i++)        {            if(i==0)            {                generate(dep,maxdep,leftnum+1,lefttotal+1,s+'(');            }            else            {                if(leftnum>0)                {                    generate(dep,maxdep,leftnum-1,lefttotal,s+')');                }            }        }    }};

递归，哼哼