对链表分段的函数，使用链表的长度信息。其次要求把归并排序的每一步过程都打印出来。自己构造一个链表类并实现，用于排序。另外生成随机数的类-Section of the list function, use the length of the message list. Second, requested that the process every step of mergesort are printed. Construct their own class and implement a li