[LeetCode82]Remove Duplicates from Sorted List II

题目：

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.

分类：Linked List

代码：维护两个指针ptr，pre

 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)
13             return head;
14         if(head && !head->next)
15             return head;
16         ListNode *newHead = new ListNode(head->val - 1);
17         newHead->next = head;
18         ListNode *pre = newHead;
19         ListNode *ptr = newHead;
20         while(head)
21         {
22             if(pre->val != head->val && (!head->next || head->val != head->next->val))
23             {
24                 ptr->next = head;
25                 ptr = ptr->next;
26             }
27             pre = head;
28             head = head->next;
29         }
30         ptr->next = NULL;
31         
32         return newHead->next;
33     }
34 };