22 Generate Parentheses

class Solution {
    public List<String> generateParenthesis(int n) {
        List<String> ans = new ArrayList<String>();
        generate(ans, 0, 0, "", n);
        return ans;
    }
    
    public void generate(List<String> ans, int open, int close, String curr, int n) {
    	if (curr.length() == n * 2)
    		ans.add(curr);
    	else {
    		if (open < n)
    			generate(ans, open + 1, close, curr + "(", n);
    		if (close < open)
    			generate(ans, open, close + 1, curr + ")", n);
    	}
    }
}