leetcode[22]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:

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

class Solution {
public:
void generate(int left, int right, string s, vector<string> &res,int n)
{
if(left==n&&right==n)
{
res.push_back(s);
return;
}
if(left<n)
{
generate(left+1, right, s+'(', res,n);
}
if(right<n&&left>right)
{
generate(left, right+1, s+')', res,n);
}
}
vector<string> generateParenthesis(int n)
{
vector<string> res;
generate(0, 0, "", res,n);
return res;
}
};