/**
     * TODO: Implement
     */
    public void remove(String str)
    {
        if(front == null) return;
        if(front.key.equals(str)) front = front.next;
        Node front.next = remove_helper(str, front);


    }

    private Node remove_helper(String str, Node node)
        {
            if(node == null) return null;
            if(node.key.equals(str)) {
                Node temp = node.next;
                node = null;
                temp.next = remove_helper(str, temp);
                return temp;
            }
            node.next = remove_helper(str, node.next);
            return node;
        }
    }