"""

Rotate List

Given a linked list, rotate the list to the right by k places, where k is

non-negative.

Reference: https://leetcode.com/problems/rotate-list/

Complexity:

Time: O(n)

Space: O(1)

"""

from __future__ import annotations

def rotate_right(head: object | None, k: int) -> object | None:

"""Rotate a linked list to the right by k positions.

Args:

head: Head node of the linked list (must have .val and .next attrs).

k: Number of positions to rotate right (non-negative).

Returns:

The new head of the rotated list.

Examples:

>>> rotate_right(None, 5) is None

True

"""

if not head or not head.next:

return head

current = head

length = 1

while current.next:

current = current.next

length += 1

current.next = head

k = k % length

for _ in range(length - k):

current = current.next

head = current.next

current.next = None

return head