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
#
class Solution:
    def ReverseList(self , head: ListNode) -> ListNode:
        # pre指向前一个结点，current指向当前节点
        #先用next_node暂存下一个结点，然后将current指向前一个结点
        #最后，pre指向current，current指向next_node，通过这种方式向右移动
        pre = None
        current = head
        while current:
            next_node = current.next
            current.next = pre
            pre = current
            current = next_node
        return pre