private void addToList(List<Integer> list, TreeNode left, TreeNode right, boolean isLeft){
    	if(isLeft){
    		if(null != left)  list.add(left.val);
    		if(null != right) list.add(right.val);
    	}else{
    		if(null != left)  list.add(0, left.val);
    		if(null != right) list.add(0, right.val);
    	}
    }