class ListNode: def __init__(self, val=0, next=None): self.val = val self.next = next def reverseList(head): current = head previous = None while current is not None: 保存当前节点的下一个节点 next_node = current.next 反转当前节点的指针 current.next = previous # 更新指针位置 previous = current current = next_node 返回反转后的链表头节点 return previous