92.反转链表2(Medium)-未掌握

LeetCode每日一题(2021.03.18)之反转链表2

给你单链表的头指针 head 和两个整数 left 和 right ，其中 left <= right 。请你反转从位置 left 到位置 right 的链表节点，返回 反转后的链表 。

示例1:

输入：head = [1,2,3,4,5], left = 2, right = 4
输出：[1,4,3,2,5]

示例2:

输入：head = [5], left = 1, right = 1
输出：[5]

提示：

• 链表中节点数目为 n
• 1 <= n <= 500
• -500 <= Node.val <= 500
• 1 <= left <= right <= n

进阶：
你可以使用一趟扫描完成反转吗？

0.0.1. 解法

# Definition for singly-linked list.
# class ListNode(object):
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution(object):
    def reverseBetween(self, head, left, right):
        """
        :type head: ListNode
        :type left: int
        :type right: int
        :rtype: ListNode
        """
        count = 1
        
        dummy = ListNode(0)
        dummy.next = head
        
        pre = dummy

        while pre.next and count < left:
            pre = pre.next
            count += 1

        cur = pre.next
        tail = cur

        while cur and count <= right:
            nxt = cur.next
            cur.next = pre.next
            pre.next = cur
            tail.next = nxt
            cur = nxt
            count += 1
        return dummy.next