[LeetCode]Generate Parentheses

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses.

For example, given n = 3, a solution set is:

"((()))", "(()())", "(())()", "()(())", "()()()"

思考：记录左右括号的数目。

class Solution {

public:

    void func(vector<string> &res,string ans,int left,int right)

    {

        if(left==0&&right==0)

        {

            res.push_back(ans);

            return;

        }

        if(left>0) func(res,ans+'(',left-1,right+1);

        if(right>0) func(res,ans+')',left,right-1);

    }

    vector<string> generateParenthesis(int n) {

        vector<string> res;

        string ans="";

        func(res,ans,n,0);

        return res;

    }

};