题解 | #删除有序链表中重复的元素-II#

#define INVALID (0xffffffff)
struct ListNode* deleteDuplicates(struct ListNode* head ) {
    struct ListNode* cur = NULL, *next = NULL, *pre = NULL;
    struct ListNode tmp = {INVALID, NULL};
    struct ListNode* p_tmp = &tmp;
    int val = INVALID;
    if (head == NULL || head->next == NULL) {
        return head;
    }
    
    pre = p_tmp;
    cur = head;
    next = cur->next;
    
    while (cur) {
        if (pre->val != cur->val
           && (next == NULL || cur->val != next->val)) {
            p_tmp->next = cur;
            p_tmp = p_tmp->next;
        }
        
        pre = cur;
        cur = cur->next;
        if (cur) {
            next = cur->next;
        }
    }
    p_tmp->next = NULL;

    return tmp.next;
}