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

.

class Solution {
public:
ListNode *deleteDuplicates(ListNode *head) {
if(head == NULL || head->next == NULL)
return head;
ListNode *pre = head;
ListNode *p_next = pre;
while(pre != NULL)
{
p_next = pre->next;
if(p_next && p_next->val == pre->val)
{
ListNode *p_del = p_next;
pre->next = p_next->next;
delete p_del;
}
else
{
pre = pre->next;
}
}
return head;
}
};