remove-duplicates-from-sorted-list

Given a sorted linked list, delete all duplicates such that each element appear only once.
For example,
Given1->1->2, return1->2.
Given1->1->2->3->3, return1->2->3.

开始用的方法不正确，每次在while循环里，先用temp给pre赋值，temp再后移，这样不行的原因是如果出现连续三个相同的节点会只删除一个。注意下面代码里的if和else。

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 *temp = head->next;        ListNode *pre = head;        while(temp!=NULL){                        if(pre->val==temp->val){                pre->next = temp->next;                temp = pre->next;            }            else{                pre = pre->next;                temp = temp->next;            }        }        return head;    }};