public static List<String> genPar(int l, int r){
		ArrayList<String> result = new ArrayList<String>();
		if(l == 0){
			StringBuilder sb = new StringBuilder();
			for(int i = 0; i < r; i++)
				sb.append(")");
			result.add(sb.toString());
			return result;
		}
		
		if(l >= 1){
			for(String val : genPar(l-1, r))
				result.add("(" + val);
		}
		if(r>l){
			for(String val : genPar(l, r-1))
				result.add(")" + val);
		}
		return result;
	}