struct ListNode* deleteNode(struct ListNode* head, int val){
    //创建哑节点
    struct ListNode* left = (struct ListNode*)malloc(sizeof(struct ListNode));
    left->next = head;
    //保留哑节点的值
     struct ListNode* p = (struct ListNode*)malloc(sizeof(struct ListNode));
     p = left;
    struct ListNode* right = head;
    //双指针删除列表中的元素
    //p才是真正意义上的哑节点
    while(left != NULL)
    {
        if(right->val == val)
        {
            left->next = right->next;
            
        }
        left = left->next;
        right = right->next;
    }
    //返回哑节点的next指针
    return p->next;
}