083 Remove Duplicates from Sorted List [Leetcode]

题目内容：

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.

题目比较简单，只需要判断当前节点是否需要删除。从Leetcode时间上看，还有更快的方法，然而在discuss中看了一下更快的方法，发现逻辑是相同的，然而没有释放被删除的节点，因此会出现内存泄露，虽然时间快了。

/**
* 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->next), *pre(head);
while(p != NULL) {
if(p->val == pre->val) {
pre->next = p->next;
delete p;
p = pre->next;
}
else {
pre = p;
p = p->next;
}
}

return head;
}
};