本程序的目的是模拟实现一个简单的单链表操作的类，可以向其中添加若干字母(A-Z)作为其节点元素。

要求：使用字符用户界面。程序功能：

1.　　可以随机选取若干个字母，添加到自制的单链表中。字母取值范围是[A,Z]

2.　　可以取得该单链表的补集（全集为A, B, C, … Z）。

3.　　可以求取两个单链表的交集。

4.　　可以求取两个单链表的并集。

5.　　可以对功能4生成的并集去除冗余元素。

-The purpose of this program is to simulate a simple operation of a singly linked list class, to which add a number of letters (AZ) as the node element. Requirements: character user interface. The program features: (1) can randomly select a number of letters added to the homemade singly linked list. The letters range [A, Z] 2. Can obtain the complement of the singly linked list (Complete A, B, C, ... Z). You can strike the intersection of two singly linked list. Can strike a singly linked list and set. 5 function 4 can be generated and set to remove redundant elements.