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:

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




class Solution {
public:
    vector<string> generateParenthesis(int n) {
        // IMPORTANT: Please reset any member data you declared, as
        // the same Solution instance will be reused for each test case.
        if(n == 0) {
            return vector<string>(1, "");
        }

        if(n == 1) {
            return vector<string>(1, "()");
        }

        vector<string> left;
        vector<string> right;
        vector<string> svec;
        int i = 0, j = 0, k = 0;
        string str;
        for(k = n - 1; k >= 0; --k) {
            left = generateParenthesis(k);
            right = generateParenthesis(n - 1 - k);
            for(i = 0; i < left.size(); ++i) {
                for(j = 0; j < right.size(); ++j) {
                    str.clear();
                    str.append("(");
                    str.append(left[i]);
                    str.append(")");
                    str.append(right[j]);
                    svec.push_back(str);
                }
            }
        }

        return svec;
    }
};

这个递归有点麻烦