human
I found an interesting problem on https://leetcode.com/problems/reverse-nodes-in-k-group/:
Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

k is a positive integer and is less than or equal to the length of the linked list. If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.



Example:

Given this linked list: 1->2->3->4->5

For k = 2, you should return: 2->1->4->3->5

For k = 3, you should return: 3->2->1->4->5

Note:

       Only constant extra memory is allowed.
       You may not alter the values in the list's nodes, only nodes itself may be changed.

I tried it in Python, but could not do it. Can you solve it?

 Write me a the Python program you requested?
assistant
#Here is the Python program you requested.

# Definition for singly-linked list.
 # class ListNode:
 #     def __init__(self, x):
 #         self.val = x
 #         self.next = None
 
 class Solution:
     def reverseKGroup(self, head, k):
         """
         :type head: ListNode
         :type k: int
         :rtype: ListNode
         """
         current = head 
         next  = None
         prev = None
         count = 0
         
         if(self.nextkthnode(head,k) is None):
             return head
         while(current is not None and count < k):
             next = current.next
             current.next = prev
             prev = current
             current = next
             count += 1
  
        
         if next is not None and self.nextkthnode(next,k) is not None:
             head.next = self.reverseKGroup(next, k)
         elif(next is not None):
             head.next = next
  
         return prev 
             
         
     def nextkthnode(self, head, k):
         for i in range(k-1):
             if(head==None):
                 return None
             head=head.next
         return head