[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.

Analysis:

class Solution {
public:
    ListNode *deleteDuplicates(ListNode *head) {
        ListNode* dummyHead = new ListNode(0);
        dummyHead->next = head;
  //use dummy head to make it easy to handle head node which is duplicate
        ListNode* prev = dummyHead;
        ListNode* curr = head;
        while(curr != NULL)
        {
   //When find a node whose value is equal to its next node
            if (curr->next != NULL && curr->val == curr->next->val)
            {
    //remove all its next nodes
                while(curr != NULL && curr->next != NULL && curr->val == curr->next->val)
                {
                    ListNode* next = curr->next;
                    curr->next = curr->next->next;
                    delete next;
                }
    //then remove itself. 
                ListNode* tmp = curr;
                prev->next = curr->next;
                curr = curr->next;
                delete tmp;
            }
            else
            {
    //otherwise, move to next node
                prev = curr;
                curr = curr->next;
            }
        }
        
        return dummyHead->next;
    }
};