数据结构--链表

这道题可以分两条路径出发，创建两个链表smallhead和largehead，smallhead指向所有比x小的值，largehead指向所有比x大的值，再将smallhead的尾部链接到largehead上。

# 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: ListNode, x: int) -> ListNode:
      # 怎么判断前后
      smallhead=ListNode(0,head)
      largehead=ListNode(0,head)
      small=smallhead
      large=largehead

      while head:
        if head.val