"""
92. Reverse Linked List II
Difficulty: Medium
https://leetcode.com/problems/reverse-linked-list-ii/

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Given the head of a singly linked list and two integers left and
right where left <= right, reverse the nodes of the list from position
left to position right, and return the reversed list.



Example 1:

Input: head = [1,2,3,4,5], left = 2, right = 4
Output: [1,4,3,2,5]

Example 2:

Input: head = [5], left = 1, right = 1
Output: [5]



Constraints:

        • The number of nodes in the list is n.

        • 1 <= n <= 500

        • -500 <= Node.val <= 500

        • 1 <= left <= right <= n



Follow up: Could you do it in one pass?
"""


# Definition for singly-linked list.
# class ListNode:
#     def __init__(self, val=0, next=None):
#         self.val = val
#         self.next = next
class Solution:
    def reverseBetween(
        self, head: ListNode | None, left: int, right: int
    ) -> ListNode | None:
        cur, prev = head, None
        while left > 1:
            prev = cur
            cur = cur.next
            left, right = left - 1, right - 1

        tail, con = cur, prev
        while right:
            third = cur.next
            cur.next = prev
            prev = cur
            cur = third
            right -= 1

        if con:
            con.next = prev
        else:
            head = prev

        tail.next = cur
        return head