题解 | #反转链表#

class ListNode:
    def __init__(self, x):
        self.val = x
        self.next = None
#
# 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
#
# 
# @param head ListNode类 
# @return ListNode类
# 先把当下的下一个存起来， 再把当前下一个变成prev, 再将prev变成当前， 最后将当前变成next
#
class Solution:
    def ReverseList(self , head: ListNode) -> ListNode:
        # write code here
        prev = None
        current = head
        while current != None:
            next = current.next
            current.next = prev
            prev = current
            current = next
        return prev