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:
        if not head:
            return head
        # write code here
        data = []
        
        # 将链表中的数据记录到data中
        while head.next:
            data.append(head.val)
            head = head.next
        data.append(head.val)
        
        result = ListNode(data[-1]) # 保留一个反向链表的头
        current = result    # 维护一个指针用于更新数据
        for i in range(1, len(data)):
            index = - i - 1         # 由于不能使用reversed将data反转，使用负数index反向遍历data
            next_node = ListNode(data[index])
            current.next = next_node
            current = next_node

        return result