LeetCode 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* term = head;
        
        ListNode* term2 = term;
        int pre = term->val;
        int tag=0;
        
        int first = 0;
        
        while(term->next!=NULL)
        {
            if(term->next->val == pre)
            {
                ListNode* temp = term->next->next;
                term->next = temp;
                tag=1;
                if(first==0)
                    first=1;
                continue;
            }
            
            
            int tag2=0;
            
            if(tag==1)
            {
                if(first==1)
                {
                    head = term2->next;
                    term2 = head;
                    first=0;
                    tag2=1;
                }
                else
                {
                    term2->next = term->next;
                }
                
            }
            if(tag!=1)
                term2 = term;
            tag=0;
            
            if(tag2==0)
                first+=2;
            
            pre = term->next->val;
            term = term->next;
            
        }
        if(tag==1)
        {
             if(first==1)
             {
                 head = term2->next;
             }
             else
             {
                 term2->next = term->next;
             }
        }
        return head;
    }
};