[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

 /**
  * Definition for singly-linked list.
  * struct ListNode {
  *     int val;
  *     ListNode *next;
  *     ListNode(int x) : val(x), next(NULL) {}
  * };
  */
 class Solution {
 public:
     ListNode* deleteDuplicates(ListNode* head) {
         if(!head)
             return head;
         if(head && !head->next)
             return head;
         ListNode *newHead = new ListNode(head->val - );
         newHead->next = head;
         ListNode *pre = newHead;
         ListNode *ptr = newHead;
         while(head)
         {
             if(pre->val != head->val && (!head->next || head->val != head->next->val))
             {
                 ptr->next = head;
                 ptr = ptr->next;
             }
             pre = head;
             head = head->next;
         }
         ptr->next = NULL;

         return newHead->next;
     }
 };