92. 反转链表 II(Medium)

题目描述

Leetcode 地址

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

样例

Input: 1->2->3->4->5->NULL, m = 2, n = 4
Ouput: 1->4->3->2->5->NULL

解题思路

代码

class Solution:
    def reverseBetween(self, head: ListNode, m: int, n: int) -> ListNode:
        pre, cur = None, head 
        for _ in range(m - 1):
            pre = cur 
            cur = cur.next
        before, after = pre, cur 

        for _ in range(n - m + 1):
            cur_next_bak = cur.next
            cur.next = pre 

            pre = cur 
            cur = cur_next_bak
        if before:
            before.next = pre 
        else:
            head = pre 
        after.next = cur 
        return head