LeetCode:Remove Duplicates from Sorted List

Problem:

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.

Solution:同Remove Duplicates from Sorted Array的思路一样，每次用结果链表的尾指针pre与遍历原链表的指针last的val作比较，不同则加入原链表。最后返回结果，注意每次加入

结果链表中，pre->next=NULL。

/**
 * 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) return head;
        ListNode *dummy=new ListNode(-1);
        
        ListNode *pre=head;
        ListNode *last=head->next;
        
        dummy->next=pre;
        pre->next=NULL;
        
        while(last!=NULL)
        {
            if(pre->val!=last->val)
            {
                pre->next=last;
                pre=pre->next;
                last=last->next;
                pre->next=NULL;
            }
            else
                last=last->next;
            
        }
        return dummy->next;
        
    }
};