def reorderList(self, head: ListNode) -> None:
"""
Do not return anything, modify head in-place instead.
"""
sentinel = ListNode(next=head)
fast = slow = head
while fast.next and fast.next.next:
fast = fast.next.next
slow = slow.next
line2 = slow.next
slow.next = None
cur = line2
prev = None
while cur:
# succ = cur.next
# cur.next = prev
# prev = cur
# cur = succ
# Concise notation
cur.next, prev, cur = prev, cur, cur.next
line2 = prev
while line2:
# temp = line2.next
# line2.next = head.next
# head.next = line2
# head = head.next.next
# line2 = temp
# Concise notation
line2.next, head.next, head, line2 = head.next, line2, head.next, line2.next
sentinel.print_all()
