leetcode solution

public class  {
    
    * @param n n pairs
    * @return All combinations of well-formed parentheses
    */
    public ArrayList<String> generateParenthesis(int n) {
        // Write your code here
        ArrayList<String> result = new ArrayList<String>();
        String temp = new String();

        helper(result, temp, n, 0, 0);

        return result;
    }
    private void helper(ArrayList<String> result, String temp, int n,
                            int leftParentheses, int rightParentheses) {
        if (temp.length() == 2 * n) {
            result.add(temp);
        }
        
        if (leftParentheses < n) {
            helper(result, temp + '(', n, leftParentheses + 1, rightParentheses);
        }
        if (rightParentheses < leftParentheses) {
            helper(result, temp + ')', n, leftParentheses, rightParentheses + 1);
        }
        
        return;
    }
}