1212121 删除完之后变为12  
思路：先拿第一个元素与之后所有做对比，相同的都删除，然后在那第二个元素与后面元素做对比，相同的删除，以此类推
Node *CompareList(Node *pHead)//删除重复元素
{
    Node *pNext,*tmp,*p1;
    if(pHead == NULL)
    {
        printf("链表为空，无法操作\n");
        exit(0);
    }
    else
    {
        p1 = pHead;
        while(p1 !=NULL)
        {
            pNext = p1->next;
            while(pNext != NULL)
        {
        
            if(p1->Elem == pNext->Elem)
            {
                tmp = pNext->next;
                free(pNext);
                pNext = tmp;
            }
            else pNext = pNext->next;
        }
            p1 = p1->next;
        }
    }
    return pHead;
}