Python学习笔记25（链表反转）

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None
class Solution:
    def reverseList(self, head):
        """
        :type head: ListNode
        :rtype: ListNode
        """
        previous = None
        while head:
            next_node = head.next
            head.next = previous
            previous = head
            head = next_node
        return previous