[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.

class Solution {public:    ListNode *deleteDuplicates(ListNode *head) {        ListNode *ptr = NULL;        ListNode *cur = head;        ListNode *head0 = NULL;        int cnt = 0;        while(cur != NULL){            ListNode *tmp = cur;            while(cur -> next != NULL && cur -> next -> val == cur -> val)                cur = cur -> next;            if(tmp == cur){                cnt ++;                if(cnt == 1) head0 = ptr = cur;                else {                    ptr -> next = cur;                    ptr = ptr -> next;                }            }            cur = cur -> next;            if(cnt >= 1)                ptr -> next = NULL;//如出现 1 2 2 2 这种情况，所以要把ptr -> next 设为NULL;        }        if(cnt == 0) return NULL;        return head0;    }};