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:

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

void parenthesis(char* str, int left, int right, int n, vector<string> &res)
	{
		if(left == right && left+right == 2*n)
		{
			stringstream ss(str);
			string tmp;
			ss>>tmp;
			//cout<<tmp<<endl;
			res.push_back(tmp);
			return;
		}
		if(left<right || left+right>=2*n)return;
		int index = left+right;
		str[index] = '(';
		parenthesis(str,left+1,right,n,res);

		str[index] = ')';
		parenthesis(str,left,right+1,n,res);
	}
	vector<string> generateParenthesis(int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<string> res;
		char* str = new char[2*n+1];
		str[2*n] = '\0';
		parenthesis(str,0,0,n,res);
		return res;
    }

第二遍的代码：

class Solution {
public:
    void backTracking(vector<string> &res, string str, int left, int right, int n)
{
	if(left < right || right + left > n*2) return;
	if(left == n && right == n) { res.push_back(str); return; }
	backTracking(res, str + "(", left + 1, right, n);
	backTracking(res, str + ")", left, right + 1, n);
}

vector<string> generateParenthesis(int n) {
        vector<string> res;
		string str = "";
		backTracking(res, str, 0, 0, n);
		return res;
    }
};