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
        if not head.next:
            return head
        if m==n:
            return head
        pre = head
        sec = head.next
        nums = 1
        while nums!=n:
            if nums<m:
                Fist = pre
                pre, sec = sec, sec.next
                nums+=1
            else:
                node = sec.next
                sec.next = pre
                pre, sec = sec, node
                nums+=1
        if m==1:
            head.next = sec
            return pre
        else:
            Fist.next.next =sec
            Fist.next = pre
            return head