leetcode 82: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

.
思路：
/**
* 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||!head->next)return head;
ListNode *newhead=0,**phead=&newhead;//phead pointer to new head pointer
while(head)
{
if(head->next&&head->val==head->next->val)
{//skip all nodes has duplicate value
int dupval=head->val;
while(head&&head->val==dupval)head=head->next;
continue;
}//assign and advance phead
else {*phead=head; phead=&((*phead)->next);}
head=head->next;
}
*phead=0;// point the next of last node to NULL
return newhead;
}
};