快慢指针

不要边界判断,直接异常梭哈

# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
#
# 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
#
# 
# @param head ListNode类 
# @return ListNode类
#
class Solution:
    def middleNode(self , head: ListNode) -> ListNode:
        if not head.next:return head
        fast,slow = head,head
        while fast or slow:
            try:
                fast = fast.next.next
                slow = slow.next
            except:
                return slow