https://leetcode.cn/problems/remove-linked-list-elements/

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution 
{
    public:
        ListNode* removeElements(ListNode* head, int val) 
        {
            if(head == nullptr)
            {
                return 0;
            }

            ListNode *head2 = new ListNode(0); // 创建新链表存储结果链表
                                               // 原因：为便于对head链表的头结点进行判断
            head2->next = head;

            ListNode *p = head2;
            while(p->next != nullptr)
            {
                if(p->next->val == val)
                {
                    p->next = p->next->next;
                }

                else
                {
                    p = p->next;
                }
            }

            return head2->next;
        }
};