如何对链表重新排序？

class ListNode:
    def __init__(self, val=0, next=None):
        self.val = val
        self.next = next

def reorderList(head):
    if not head or not head.next:
        return head

    # 找到链表的中间节点
    slow = head
    fast = head
    while fast.next and fast.next.next:
        slow = slow.next
        fast = fast.next.next

    # 将链表从中间节点处断开
    second_half = slow.next
    slow.next = None

    # 反转第二个链表
    prev = None
    curr = second_half
    while curr:
        next_node = curr.next
        curr.next = prev
        prev = curr
        curr = next_node
    second_half = prev

    # 合并两个链表
    first_half = head
    while second_half:
        next_node = first_half.next
        first_half.next = second_half
        second_half = second_half.next
        first_half.next.next = next_node
        first_half = next_node

    return head