static void parenthesisHelper(int left, int right, String s, List<String>rel) {
		if (left<0||right<0||left>right)
			return;
		if (left==0&&right==0) {
			rel.add(s);
			return;
		}
		parenthesisHelper(left-1,right,s+"(",rel);
		parenthesisHelper(left,right-1,s+")",rel);
	}