文巾解题 206. 反转链表

Posted 2021-09-06 UQI-LIUWJ

1 题目描述

2 解题思路

2.1 创建辅助链表

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        if(head==None):
            return None
        tmp=ListNode(head.val)
        
        ret=ListNode(head.val)
        while(head.next):
            
            head=head.next
            ret=ListNode(head.val)
            ret.next=tmp
            tmp=ret
        return ret

2.2

# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseList(self, head: ListNode) -> ListNode:
        if(head==None):
            return None
        prev=None
        cur=head
        while(cur!=None):
            temp=cur.next #暂存下一个节点
            cur.next=prev #使当前索引到的节点指向之前已经倒转好的链表
            prev=cur#倒转的链表向后进一位
            cur=temp # 未索引的列表向后退一位
        return prev