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:
        # write code here
        dummy = p0 = ListNode(0)
        dummy.next = p0.next = head
        for _ in range(m - 1):
            p0 = p0.next
        
        pre = None
        cur = p0.next

        for _ in range(n - m + 1):
            nxt = cur.next
            cur.next = pre
            pre = cur
            cur = nxt
        p0.next.next = cur
        p0.next = pre
        return dummy.next