反转链表 -- 每日一题05

'''
先取出第一个节点，置空next，取名为tail
然后依次取出节点，将取出节点的next指向tail，然后tail调至取出的节点
'''
class Solution:
    def ReverseList(self , head: ListNode) -> ListNode:
        # write code here
        if head == None or head.next==None:
            return head
        tail = head
        # 先将head地址换了
        head = head.next
        tail.next = None
        while head is not None:
            temp = head.next
            head.next = tail
            tail = head
            head = temp
        return tail