generating parentheses

gistfile1.txt

public ArrayList<String> generateParenthesis(int n) {
        String left = "";
        String right = "";
        ArrayList<String> res = new ArrayList<String>();
        String oneSolu = "";
        for (int i=0; i<n; i++) {
            left += "(";
            right += ")";
        }
        
        Generate(n, n, res, oneSolu);
        
        return res;
}
    
private void Generate(int l, int r, ArrayList<String> res, String oneSolu) {
        if (l==0 && r==0) {
            res.add(oneSolu);
            return ;
        }
        
        //add left
        if (l > 0) {
            String t = oneSolu;
            t += "(";
            Generate(l-1, r, res, t);
        }
        
        if (r>l) {
            String t = oneSolu;
            t += ")";
            Generate(l, r-1, res, t);
        }
}