Reverse a Linked List in groups of given size

Given a linked list of size N$.$ The task is to reverse every k nodes $($where k is an input to the function$)$ in the linked list. If the number of nodes is not a multiple of k then left$-$out nodes, in the end, should be considered as a group and must be reversed $($See Example $2$ for clarification$).$

Example $1$:

Input:

LinkedList: $1->2->2->4->5->6->7->8$

K $=4$

Output: $42218765$

Explanation:

The first $4$ elements $1,2,2,4$ are reversed first

and then the next $4$ elements $5,6,7,8.$ Hence, the

resultant linked list is $4->2->2->1->8->7->6->5.$

Example $2$:

Input:

LinkedList: $1->2->3->4->5$

K $=3$

Output: $32154$

Explanation:

The first $3$ elements are $1,2,3$ are reversed

first and then elements $4,5$ are reversed.Hence,

the resultant linked list is $3->2->1->5->4.$

Your Task:

You don't need to read input or print anything. Your task is to complete the function reverse$()$ which should reverse the linked list in group of size k and return the head of the modified linked list.

Expected Time Complexity : O$($N$)$

Expected Auxilliary Space : O$(1)$

Constraints:

$1<=$ N $<=105$

$1<=$ k $<=$ N please provide the detailed solution.