leecode第86题. 分隔链表(https://leetcode.cn/problems/partition-list/description/?envType=study-plan-v2&envId=top-interview-150)

以下是我的代码。
主要思想是,将小于x的Node放入小链表,将大于x的Node放入大链表,最后把小链表与大链表连起来。
# Definition for singly-linked list.
# class ListNode:
# def __init__(self, val=0, next=None):
# self.val = val
# self.next = next
class Solution:
def partition(self, head: Optional[ListNode], x: int) -> Optional[ListNode]:
presmall = ListNode()
points = presmall
prebig = ListNode()
pointb = prebig
point = head
while point:
if point.val < x:
points.next = point
points = point
else:
pointb.next = point
pointb = point
point = point.next
points.next = prebig.next
return presmall.next运行结果如下:

经过排查,我发现当point遍历至最后一个Node时,points = point这一行代码无法运行,最终导致超出内存限制,可是我没有明白问题出在哪里。球球大佬们帮我解答一下,球球了。