list_node * remove_rep(list_node * head)
{
    //////在下面完成代码
    if(head == nullptr || head->next == nullptr) return head;
    map<int,int> Map;
    list_node* cur = head;
    Map[cur->val]++;
    while(cur->next != nullptr) {
        if(++Map[cur->next->val] > 1) {
            Map[cur->next->val] = 1;
            cur->next = cur->next->next;
        } else
            cur = cur->next;
    }
    return head;
}