Leetcode: Remove Duplicates from Sorted List

Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,

Given 

1->1->2

, return 

1->2

.

Given 

1->1->2->3->3

, return 

1->2->3

.

/**
* 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) {
// Note: The Solution object is instantiated only once.
if(head==NULL)return head;
ListNode* pre = head->next;
ListNode* p=head;
while(pre)
{
if(p->val == pre->val)
{
ListNode* tmp = pre;
pre = pre->next;
p->next = pre;
delete tmp;
}else{
p = pre;
pre=pre->next;
}
}
return head;
}
};

精简代码：

/**
* 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 == NULL || head->next == NULL) return head;
ListNode* p = head;
ListNode* q = head->next;
while(q){
while(q && q->val == p->val) q = q->next;
p->next = q;
if(q) {p = p->next; q=q->next;}
}
return head;
}
};