class ListNode:
  def __init__(self, x):
    self.val = x
    self.next = None


class Solution:
  def deleteNode(self, head: ListNode, val: int) -> ListNode:
    tempHead = ListNode(None) # 构建哨兵节点
    tempHead.next = head

    prePtr = tempHead # 使用双指针
    postPtr = head

    while postPtr:
      if postPtr.val == val:
        prePtr.next = postPtr.next
        break
      prePtr = prePtr.next
      postPtr = postPtr.next
    return tempHead.next

struct ListNode {
   int val;
   ListNode *next;
   ListNode(int x) : val(x), next(NULL) {}
 };

class Solution {
public:
  ListNode* deleteNode(ListNode* head, int val) {
    ListNode *tempHead = new ListNode(-1); // 哨兵节点,创建节点一定要用new!!!!!!!!!!!!!!
    tempHead->next = head;

    ListNode *prePtr = tempHead;
    ListNode *postPtr = head;

    while (postPtr) {
      if (postPtr->val == val) {
        prePtr->next = postPtr->next; // 画图确定指针指向关系，按照箭头确定指向
        break;
      }
      postPtr = postPtr->next;
      prePtr = prePtr->next;
    }
    return tempHead->next;
  }
};