虚拟头节点秒杀链表问题

// c++
ListNode* deleteDuplicates(ListNode* head) {
  /* 创建虚拟头节点 */
  ListNode* dummyHead = new ListNode(0);
  dummyHead->next = head;

  ListNode* pre = dummyHead;
  while (pre->next != nullptr) {
    ListNode *cur = pre->next;
    /* 当前节点的值等于其下一节点的值，右移当前节点到其下一节点 */
    while (cur->next != nullptr && cur->val == cur->next->val) {
      cur = cur->next;
    }

    /* 当前节点不是 pre 节点的下一节点，则将 pre 节点的下一节点指向当前
      节点的下一节点，相当于删除当前所有含跟当前节点值相等的节点 */
    if (cur != pre->next) {
      pre->next = cur->next;
    /* 否则，pre 节点右移 */
    } else {
      pre = pre->next;
    }
  }

  /* 释放虚拟头节点空间，防止内存泄漏 */
  ListNode* retNode = dummyHead->next;
  delete dummyHead;
  return retNode;
}

// c++
ListNode* deleteDuplicates(ListNode* head) {
  if (head == nullptr || head->next == nullptr) {
    return head;
  }

  if (head->val == head->next->val) {
    while (head->next != nullptr && head->val == head->next->val) {
      head = head->next;
    }
    return deleteDuplicates(head->next);
  } else {
    head->next = deleteDuplicates(head->next);
    return head;
  }
}