82. Remove Duplicates from Sorted List II

/**
 * 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 *write=head,*read=head,*tail;
        int count=0,cur=head->val,res=0;
        while(read!=NULL)
        {
            if(read->val==cur)
            {
                count++;
                read=read->next;
            }    
            else
            {
                if(count==1)
                {
                    write->val=cur;
                    tail=write;
                    write=write->next;
                    res++;
                }
                cur=read->val;
                count=1;
                read=read->next;
            }
        }
        if(count==1)
        {
            write->val=cur;
            tail=write;
            write=write->next;
            res++;
        }    
        if(res==0)
            return NULL;
        else
        {
            tail->next=NULL;
            return head;
        }
    }
};

双指针压缩链表，一个读指针，一个写指针，问题不大