LeetCode OJ 82. Remove Duplicates from Sorted List II

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* deleteDuplicates(struct ListNode* head) {
    struct ListNode *pre_node, *this_node, *tmp_head;
    int tmp;
    
    while(NULL != head&&NULL != head->next){
        this_node = head->next;
        tmp = head->val;
        while(NULL != this_node){
            if(this_node->val == tmp){
                this_node = this_node->next;
            }
            else{
                break;
            }
        }
        if(head->next != this_node)
            head = this_node;
        else
            break;
    }
    if(NULL == head||NULL == head->next)
        return head;
    tmp_head = head;
    pre_node = head;
    while(NULL != pre_node){
        head = pre_node->next;
        while(NULL != head&&NULL != head->next){
            this_node = head->next;
            tmp = head->val;
            while(NULL != this_node){
                if(this_node->val == tmp){
                    this_node = this_node->next;
                }
                else{
                    break;
                }
            }
            if(head->next != this_node)
            head = this_node;
            else
                break;
        }
        pre_node->next = head;
        if(NULL == pre_node)
            break;
        pre_node = pre_node->next;
    }
    return tmp_head;
}