/**
 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */
/**
 * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
 * @author Senky
 * @date 2023.04.23
 * @par url https://www.nowcoder.com/creation/manager/content/584337070?type=column&status=-1
 * @param head ListNode类 
 * @return ListNode类
 */
struct ListNode* deleteDuplicates(struct ListNode* head ) {
    // write code here
    struct ListNode* pre = NULL;
    struct ListNode* cur = head;
    if(cur)
    {
        pre = cur;
        cur = cur->next;
    }

    while(cur)
    {
        if(cur->val == pre->val)
        {
            cur = cur->next;
            pre->next = cur;
            continue;
        }
        pre = pre->next;
        cur = cur->next;
    }
    return head;
}

图解：