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:

[
"((()))",
"(()())",
"(())()",
"()(())",
"()()()"
]

answer:

class Solution {
public:
vector<string> generateParenthesis(int n) {
vector<string> result;
string str = "";
addPar(result,str,n,0);
return result;
}

void addPar(vector<string> & result, string str, int left, int right){
if(left == 0 && right == 0){
result.push_back(str);
return;
}
if(left > 0){
addPar(result, str + "(", left - 1, right + 1);
}
if(right > 0){
addPar(result, str + ")", left, right - 1);
}
}
};