Remove Duplicates from Sorted List

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.

For example,
Given 1->2->3->3->4->4->5, return 1->2->5.
Given 1->1->1->2->3, return 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)     {        if (0 == head) return 0;        ListNode dummy(0), *pre = &dummy;        dummy.next = head;                while(pre->next != 0 && pre->next->next != 0)        {            if (pre->next->val != pre->next->next->val)               pre = pre->next;            else            {                int val = pre->next->val;                ListNode* cur = pre->next;                while(cur != 0 && cur->val == val)                {                    pre->next = cur->next;                    delete cur;                    cur = pre->next;                }            }        }        return dummy.next;    }};