leetcode——206. 反转链表

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, x):
#         self.val = x
#         self.next = None

class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        new_head=None
        while head:
            tmp=head.next
            head.next=new_head
            new_head=head
            head=tmp
        return new_head