Linked List Zip

1def reorderList(head: Optional[ListNode]) -> None:
2    if not head or not head.next:
3        return
4    slow = head
5    fast = head
6    while fast and fast.next:
7        slow = slow.next
8        fast = fast.next.next
9    second = slow.next
10    slow.next = None
11    prev = None
12    while second:
13        nxt = second.next
14        second.next = prev
15        prev = second
16        second = nxt
17    first = head
18    second = prev
19    while second:
20        tmp1 = first.next
21        tmp2 = second.next
22        first.next = second
23        second.next = tmp1
24        first = tmp1
25        second = tmp2