1.指针未归零，造成死循环。
2.输出错误，导致不知道哪里错了
class Solution:
def insertionSortList(self, head: ListNode) -> ListNode:
res =ListNode(None)
while (head != None):
cur = head
head = head.next
cur.next=None #指针归零很重要，不然会造成循环指针，这里三个顺序不能变
tmp = res.next
pre = res
while tmp != None and tmp.val<cur.val:
pre=pre.next
tmp = tmp.next
cur.next = tmp
pre.next = cur
return res.next
