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) {
std::vector<std::string> result;
generate("", n, n, result);
return result;
}
private:
void generate(std::string item, int left, int right, std::vector<std::string> &result)
{
if(left==0&&right==0)
{
result.push_back(item);
return;
}
if(left>0)
{
generate(item+'(', left-1, right, result);
}
if(left<right)
{
generate(item+')', left, right-1, result);
}
}
};