leetcode[82]Remove Duplicates from Sorted List II

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(head==NULL||head->next==NULL)return head;

    ListNode *tmp=head->next;

    ListNode *res=new ListNode(0);

    res->next=head;

    ListNode *p=res->next;

    ListNode *pre=res;

    int value=head->val;

    while(tmp!=NULL)

    {

        if(p->val!=tmp->val&&value!=tmp->val)

        {

            p->next=tmp;

            pre=p;

            p=p->next;

            value=tmp->val;

        }

        else

        {

            p=pre;

        }

        tmp=tmp->next;

    }

    p->next=NULL;

    return res->next;

    }

};