LintCode-剑指Offer-(112)删除排序链表中的重复元素

class Solution {public:    /**    * @param head: The first node of linked list.    * @return: head node    */    ListNode *deleteDuplicates(ListNode *head) {        // write your code here        ListNode* tmp = head;        ListNode* pre = NULL;        while (tmp!=NULL){            pre = tmp;            tmp = tmp->next;            while (tmp!=NULL&&tmp->val==pre->val){                pre->next = tmp->next;                delete tmp;                tmp = pre->next;            }        }        return head;    }};