题解 | #链表内指定区间反转#

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 
# @param m int整型 
# @param n int整型 
# @return ListNode类
#

class Solution:
    def reverseBetween(self, head: ListNode, m: int, n: int) -> ListNode:
        if not head:
            return None

        # 创建一个虚拟节点 dummy，作为链表的起始点
        dummy = ListNode(0)
        dummy.next = head

        # 初始化指针
        pre = dummy
        for _ in range(m - 1):
            pre = pre.next

        # 反转链表
        cur = pre.next
        for _ in range(n - m):
            temp = cur.next
            cur.next = temp.next
            temp.next = pre.next
            pre.next = temp

        return dummy.next