反转链表

举例说明：

"""单链表"""
class Node:
    def __init__(self, item):
        self.item = item
        self.next = None

'''链表反转'''
def reverse(head):
    prev = None
    current = head

    while current:
        next_node = current.next  # 临时保存下一个节点
        current.next = prev  # 反转指针
        prev = current  # prev 前移
        current = next_node  # current 前移

    return prev  # 返回新的头节点

双链表同理

'''定义双向链表'''
class ListNode(object):
    def __init__(self, data=0, prev=None, next=None):
        self.data = data
        self.prev = prev
        self.next = next

def reverseListNode(head):
    prev = None
    current = head
    while current:
        next_node = current.next
        current.next = prev
        current.prev = next_node
        prev = current
        current = next_node
    return prev