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class Solution {
public:
    vector<string> ans;
    void genStep(string &item,int n,int countLeft,int countRight)
    {
        if(countLeft == n && countRight == n)
        {
            ans.push_back(item);
            return;
        }
        if(countLeft < n)
        {
            countLeft++;
            item.insert(item.length(),"(");
            genStep(item,n,countLeft,countRight);
            countLeft--;
            item = item.erase(item.length()-1,1);
        }
        if(countRight < n && countLeft > countRight)
        {
            countRight++;
            item.insert(item.length(),")");
            genStep(item,n,countLeft,countRight);
            countRight--;
            item = item.erase(item.length()-1,1);
        }
    }
    vector<string> generateParenthesis(int n) {
        ans.clear();
        if(n == 0)return ans;
        int countLeft = 1;
        int countRight = 0;
        string item = "(";
        genStep(item,n,countLeft,countRight);
        return ans;
    }
};