[leetcode]Generate Parentheses

class Solution {
public:
int tot;
vector<string> ans;
void search(string p , int left , int right){
if(left > tot || right > tot) return;
if(left == tot && right == tot){
ans.push_back(p);
return;
}
if(left < right) return;
search(p + "(" , left + 1 , right);
search(p + ")" , left , right + 1);
}

vector<string> generateParenthesis(int n) {
// Note: The Solution object is instantiated only once and is reused by each test case.
tot = n;
ans.clear();
search("(" , 1 , 0);
return ans;
}
};