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.

Example 1:

Input:

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

K = 4

Output: 4 2 2 1 8 7 6 5 

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: 3 2 1 5 4 

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.

c++ implementation:

struct node *reverse (struct node* head, int k)
{
	struct node* current = head;
	struct node* next = NULL;
	struct node* prev = NULL;
	int count = 0; 
	
	while (current != NULL && count < k)
	// reversing k elements :
	{
		next = current->next;             // marking next node
		current->next = prev;             // reversing link
		prev = current;                   // updating prev
		current = next;                   // updating current
		count++;
	}
	
	if (next != NULL)       // checking if there are nodes ahead
    	head->next = reverse(next, k);    // reversing those recursively
    
	return prev;            // returning new head
}

Time Complexity: O(n)