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 or m == n:
            return head
        
        dummy = ListNode(0)
        dummy.next = head
        pre = dummy

        for _ in range(m-1):
            pre = pre.next

        current = pre.next

        for _ in range(n-m):
            next_node = current.next
            current.next = next_node.next
            next_node.next = pre.next
            pre.next = next_node
        
        return dummy.next