【Leetcode】Remove Duplicates from Sorted List II

Given a sorted linked list, delete all nodes that have duplicate numbers,
leaving only distinct numbers from the original list.

For
example,
Given 1->2->3->3->4->4->5,
return 1->2->5.
Given 1->1->1->2->3,
return 2->3.

 1 /**

 2  * Definition for singly-linked list.

 3  * struct ListNode {

 4  *     int val;

 5  *     ListNode *next;

 6  *     ListNode(int x) : val(x), next(NULL) {}

 7  * };

 8  */

 9 class Solution {

10 public:

11     ListNode *deleteDuplicates(ListNode *head) {

12         if (head == nullptr || head->next == nullptr)

13             return head;

14         ListNode dummy(-1);

15         dummy.next = head;

16         ListNode *prev = &dummy, *cur = head;

17         while (cur != nullptr) {

18             bool flag = false;

19             while (cur->next != nullptr && cur->val == cur->next->val) {

20                 flag = true;

21                 prev->next = cur->next;

22                 delete cur;

23                 cur = prev->next;

24             }

25             if (flag) {

26                 prev->next = cur->next;

27                 delete cur;

28                 cur = prev->next;

29             } else {

30                 prev = cur;

31                 cur = cur->next;

32             }

33         }

34         return dummy.next;

35     }

36 };