import pyutil as pyu
pyu.get_local_pyinfo()

print(pyu.ps2("python-dotenv"))

from typing import List

class Solution:
  def reverseKGroup(self, head: Optional[ListNode], k: int) -> Optional[ListNode]:
    if not head:
      return None

    tail = head

    for _ in range(k):
      if not tail:  # Less than k nodes, do nothing
        return head
      tail = tail.next

    newHead = self._reverse(head, tail)
    head.next = self.reverseKGroup(tail, k)
    return newHead

  # Reverses [head, tail)
  def _reverse(self, head: Optional[ListNode], tail: Optional[ListNode]) -> Optional[ListNode]:
    prev = None
    curr = head

    while curr != tail:
      next = curr.next
      curr.next = prev
      prev = curr
      curr = next

    return prev

new Solution().reverseKGroup()