struct ListNode* deleteDuplicates(struct ListNode* head){
    struct ListNode* cur = head;
    if(head == NULL)
    {
        return NULL;
    }
    while(cur->next != NULL)
    {
        if(cur->val == cur->next->val)
        {
            cur->next = cur->next->next;
        }
        else
        {
            cur = cur->next;
        }
    }
    return head;
}